xref: /dports/databases/percona57-server/percona-server-5.7.36-39/sql/sql_cache.cc

/* Copyright (c) 2000, 2021, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */

/*
  Description of the query cache:

1. Query_cache object consists of
	- query cache memory pool (cache)
	- queries hash (queries)
	- tables hash (tables)
	- list of blocks ordered as they allocated in memory
(first_block)
	- list of queries block (queries_blocks)
	- list of used tables (tables_blocks)

2. Query cache memory pool (cache) consists of
	- table of steps of memory bins allocation
	- table of free memory bins
	- blocks of memory

3. Memory blocks

Every memory block has the following structure:

+----------------------------------------------------------+
|      Block header (Query_cache_block structure)	   |
+----------------------------------------------------------+
|Table of database table lists (used for queries & tables) |
+----------------------------------------------------------+
|		  Type depended header			   |
|(Query_cache_query, Query_cache_table, Query_cache_result)|
+----------------------------------------------------------+
|			Data ...			   |
+----------------------------------------------------------+

Block header consists of:
- type:
  FREE		Free memory block
  QUERY		Query block
  RESULT	Ready to send result
  RES_CONT	Result's continuation
  RES_BEG	First block of results, that is not yet complete,
		written to cache
  RES_INCOMPLETE  Allocated for results data block
  TABLE		Block with database table description
  INCOMPLETE	The destroyed block
- length of block (length)
- length of data & headers (used)
- physical list links (pnext/pprev) - used for the list of
  blocks ordered as they are allocated in physical memory
- logical list links (next/prev) - used for queries block list, tables block
  list, free memory block lists and list of results block in query
- number of elements in table of database table list (n_tables)

4. Query & results blocks

Query stored in cache consists of following blocks:

more		      more
recent+-------------+ old
<-----|Query block 1|------> double linked list of queries block
 prev |		    | next
      +-------------+
    <-|  table 0    |-> (see "Table of database table lists" description)
    <-|  table 1    |->
      |  ...	    |		+--------------------------+
      +-------------+	 +-------------------------+	   |
NET   |		    |	 |	V		   V	   |
struct|		    |	 +-+------------+   +------------+ |
<-----|query header |----->|Result block|-->|Result block|-+ doublelinked
writer|		    |result|		|<--|		 |   list of results
      +-------------+	   +------------+   +------------+
      |charset	    |	   +------------+   +------------+ no table of dbtables
      |encoding +   |	   |   result	|   |	result	 |
      |query text   |<-----|   header	|   |	header	 |------+
      +-------------+parent|		|   |		 |parent|
	    ^		   +------------+   +------------+	|
	    |		   |result data |   |result data |	|
	    |		   +------------+   +------------+	|
	    +---------------------------------------------------+

First query is registered. During the registration query block is
allocated. This query block is included in query hash and is linked
with appropriate database tables lists (if there is no appropriate
list exists it will be created).

Later when query has performed results is written into the result blocks.
A result block cannot be smaller then QUERY_CACHE_MIN_RESULT_DATA_SIZE.

When new result is written to cache it is appended to the last result
block, if no more  free space left in the last block, new block is
allocated.

5. Table of database table lists.

For quick invalidation of queries all query are linked in lists on used
database tables basis (when table will be changed (insert/delete/...)
this queries will be removed from cache).

Root of such list is table block:

     +------------+	  list of used tables (used while invalidation of
<----|	Table	  |-----> whole database)
 prev|	block	  |next			     +-----------+
     |		  |	  +-----------+      |Query block|
     |		  |	  |Query block|      +-----------+
     +------------+	  +-----------+      | ...	 |
  +->| table 0	  |------>|table 0    |----->| table N	 |---+
  |+-|		  |<------|	      |<-----|		 |<-+|
  || +------------+	  | ...       |      | ...	 |  ||
  || |table header|	  +-----------+      +-----------+  ||
  || +------------+	  | ...       |      | ...	 |  ||
  || |db name +   |	  +-----------+      +-----------+  ||
  || |table name  |					    ||
  || +------------+					    ||
  |+--------------------------------------------------------+|
  +----------------------------------------------------------+

Table block is included into the tables hash (tables).

6. Free blocks, free blocks bins & steps of freeblock bins.

When we just started only one free memory block  existed. All query
cache memory (that will be used for block allocation) were
containing in this block.
When a new block is allocated we find most suitable memory block
(minimal of >= required size). If such a block can not be found, we try
to find max block < required size (if we allocate block for results).
If there is no free memory, oldest query is removed from cache, and then
we try to allocate memory. Last step should be repeated until we find
suitable block or until there is no unlocked query found.

If the block is found and its length more then we need, it should be
split into 2 blocks.
New blocks cannot be smaller then min_allocation_unit_bytes.

When a block becomes free, its neighbor-blocks should be tested and if
there are free blocks among them, they should be joined into one block.

Free memory blocks are stored in bins according to their sizes.
The bins are stored in size-descending order.
These bins are distributed (by size) approximately logarithmically.

First bin (number 0) stores free blocks with
size <= query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2.
It is first (number 0) step.
On the next step distributed (1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
QUERY_CACHE_MEM_BIN_PARTS_MUL bins. This bins allocated in interval from
query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 to
query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 >>
QUERY_CACHE_MEM_BIN_STEP_PWR2
...
On each step interval decreases in 2 power of
QUERY_CACHE_MEM_BIN_STEP_PWR2
times, number of bins (that distributed on this step) increases. If on
the previous step there were N bins distributed , on the current there
would be distributed
(N + QUERY_CACHE_MEM_BIN_PARTS_INC) * QUERY_CACHE_MEM_BIN_PARTS_MUL
bins.
Last distributed bin stores blocks with size near min_allocation_unit
bytes.

For example:
	query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 = 100,
	min_allocation_unit = 17,
	QUERY_CACHE_MEM_BIN_STEP_PWR2 = 1,
	QUERY_CACHE_MEM_BIN_PARTS_INC = 1,
	QUERY_CACHE_MEM_BIN_PARTS_MUL = 1
	(in followed picture showed right (low) bound of bin):

      |       100>>1	 50>>1	      |25>>1|
      |		 |	   |	      |  |  |
      | 100  75 50  41 33 25  21 18 15| 12  | -  bins right (low) bounds

      |\---/\-----/\--------/\--------|---/ |
      |  0     1	2	   3  |     | - steps
       \-----------------------------/ \---/
	bins that we store in cache	this bin showed for example only


Calculation of steps/bins distribution is performed only when query cache
is resized.

When we need to find appropriate bin, first we should find appropriate
step, then we should calculate number of bins that are using data
stored in Query_cache_memory_bin_step structure.

Free memory blocks are sorted in bins in lists with size-ascending order
(more small blocks needed frequently then bigger one).

7. Packing cache.

Query cache packing is divided into two operation:
	- pack_cache
	- join_results

pack_cache moved all blocks to "top" of cache and create one block of free
space at the "bottom":

 before pack_cache    after pack_cache
 +-------------+      +-------------+
 | query 1     |      | query 1     |
 +-------------+      +-------------+
 | table 1     |      | table 1     |
 +-------------+      +-------------+
 | results 1.1 |      | results 1.1 |
 +-------------+      +-------------+
 | free        |      | query 2     |
 +-------------+      +-------------+
 | query 2     |      | table 2     |
 +-------------+ ---> +-------------+
 | table 2     |      | results 1.2 |
 +-------------+      +-------------+
 | results 1.2 |      | results 2   |
 +-------------+      +-------------+
 | free        |      | free        |
 +-------------+      |             |
 | results 2   |      |             |
 +-------------+      |             |
 | free        |      |             |
 +-------------+      +-------------+

pack_cache scan blocks in physical address order and move every non-free
block "higher".

pack_cach remove every free block it finds. The length of the deleted block
is accumulated to the "gap". All non free blocks should be shifted with the
"gap" step.

join_results scans all complete queries. If the results of query are not
stored in the same block, join_results tries to move results so, that they
are stored in one block.

 before join_results  after join_results
 +-------------+      +-------------+
 | query 1     |      | query 1     |
 +-------------+      +-------------+
 | table 1     |      | table 1     |
 +-------------+      +-------------+
 | results 1.1 |      | free        |
 +-------------+      +-------------+
 | query 2     |      | query 2     |
 +-------------+      +-------------+
 | table 2     |      | table 2     |
 +-------------+ ---> +-------------+
 | results 1.2 |      | free        |
 +-------------+      +-------------+
 | results 2   |      | results 2   |
 +-------------+      +-------------+
 | free        |      | results 1   |
 |             |      |             |
 |             |      +-------------+
 |             |      | free        |
 |             |      |             |
 +-------------+      +-------------+

If join_results allocated new block(s) then we need call pack_cache again.

7. Interface
The query cache interfaces with the rest of the server code through 7
functions:
 1. Query_cache::send_result_to_client
       - Called before parsing and used to match a statement with the stored
         queries hash.
         If a match is found the cached result set is sent through repeated
         calls to net_write_packet. (note: calling thread doesn't have a regis-
         tered result set writer: thd->net.query_cache_query=0)
 2. Query_cache::store_query
       - Called just before handle_select() and is used to register a result
         set writer to the statement currently being processed
         (thd->net.query_cache_query).
 3. query_cache_insert
       - Called from net_write_packet to append a result set to a cached query
         if (and only if) this query has a registered result set writer
         (thd->net.query_cache_query).
 4. Query_cache::invalidate
    Query_cache::invalidate_locked_for_write
       - Called from various places to invalidate query cache based on data-
         base, table and myisam file name. During an on going invalidation
         the query cache is temporarily disabled.
 5. Query_cache::flush
       - Used when a RESET QUERY CACHE is issued. This clears the entire
         cache block by block.
 6. Query_cache::resize
       - Used to change the available memory used by the query cache. This
         will also invalidate the entrie query cache in one free operation.
 7. Query_cache::pack
       - Used when a FLUSH QUERY CACHE is issued. This changes the order of
         the used memory blocks in physical memory order and move all avail-
         able memory to the 'bottom' of the memory.


TODO list:

  - Delayed till after-parsing qache answer (for column rights processing)
  - Optimize cache resizing
      - if new_size < old_size then pack & shrink
      - if new_size > old_size copy cached query to new cache
  - Move MRG_MYISAM table type processing to handlers, something like:
        tables_used->table->file->register_used_filenames(callback,
                                                          first_argument);
  - QC improvement suggested by Monty:
    - Add a counter in open_table() for how many MERGE (ISAM or MyISAM)
      tables are cached in the table cache.
      (This will be trivial when we have the new table cache in place I
      have been working on)
    - After this we can add the following test around the for loop in
      is_cacheable::

      if (thd->temp_tables || global_merge_table_count)

    - Another option would be to set thd->lex->safe_to_cache_query to 0
      in 'get_lock_data' if any of the tables was a tmp table or a
      MRG_ISAM table.
      (This could be done with almost no speed penalty)
*/

#include "my_global.h"                          /* NO_EMBEDDED_ACCESS_CHECKS */
#include "sql_cache.h"
#include "sql_parse.h"                          // check_table_access
#include "tztime.h"                             // struct Time_zone
#include "auth_common.h"                        // SELECT_ACL
#include "sql_base.h"                           // TMP_TABLE_KEY_EXTRA
#include "debug_sync.h"                         // DEBUG_SYNC
#include "opt_trace.h"
#include "sql_table.h"
#include <m_ctype.h>
#include <my_dir.h>
#include <hash.h>
#include "../storage/myisammrg/ha_myisammrg.h"
#include "../storage/myisammrg/myrg_def.h"
#include "probes_mysql.h"
#include "transaction.h"

#include "query_strip_comments.h"

/*
  Number of bytes to be allocated in a query cache buffer in addition to the
  query string length.

  The query buffer layout is:

  buffer :==
    <statement>   The input statement(s)
    '\0'          Terminating null char
    <db_length>   Length of following current database name (size_t)
    <db_name>     Name of current database
    <flags>       Flags struct
*/
#define QUERY_BUFFER_ADDITIONAL_LENGTH(db_length)               \
  (1 + sizeof(size_t) + db_length + QUERY_CACHE_FLAGS_SIZE)

QueryStripComments::QueryStripComments()
{
  buffer = 0;
  length = 0;
  buffer_length = 0;
}
QueryStripComments::~QueryStripComments()
{
  cleanup();
}

inline bool query_strip_comments_is_white_space(char c)
{
  return ((' ' == c) || ('\t' == c) || ('\r' == c) || ('\n' ==c ));
}
void QueryStripComments::set(LEX_CSTRING query, uint additional_length)
{
  uint new_buffer_length = query.length + additional_length;
  if(new_buffer_length > buffer_length)
  {
    cleanup();
    buffer= (char*)my_malloc(key_memory_Query_cache, new_buffer_length,
                             MYF(0));
  }
  uint query_position = 0;
  uint position = 0;
  // Skip whitespaces from begin
  while ((query_position < query.length)
         && query_strip_comments_is_white_space(query.str[query_position]))
  {
    ++query_position;
  }
  long int last_space = -1;
  while (query_position < query.length)
  {
    char current = query.str[query_position];
    bool insert_space = false; // insert space to buffer, (IMPORTANT) don't update query_position
    switch(current)
    {
    case '\'':
    case '"':
      {
        buffer[position++] = query.str[query_position++]; // copy current symbol
        while(query_position < query.length)
        {
          if(current == query.str[query_position]) // found pair quote
          {
            break;
          }
          buffer[position++] = query.str[query_position++]; // copy current symbol
        }
        break;
      }
    case '/':
      {
        if(((query_position + 2) < query.length)
           && ('*' == query.str[query_position+1])
           && ('!' != query.str[query_position+2]))
        {
          query_position += 2; // skip "/*"
          do
          {
            if('*' == query.str[query_position]
               && '/' == query.str[query_position+1]) // check for "*/"
            {
              query_position += 2; // skip "*/"
              insert_space = true;
              break;
            }
            else
            {
              ++query_position;
            }
          }
          while(query_position < query.length);
          if(!insert_space)
          {
            continue;
          }
        }
        break;
      }
    case '-':
      {
        if(query.str[query_position+1] == '-')
        {
          ++query_position; // skip "-", and go to search of "\n"
        }
        else
        {
          break;
        }
      }
      // fallthrough
    case '#':
      {
        do
        {
          ++query_position; // skip current symbol (# or -)
          if('\n' == query.str[query_position])  // check for '\n'
          {
            ++query_position; // skip '\n'
            insert_space = true;
            break;
          }
        }
        while(query_position < query.length);
        if(insert_space)
        {
          break;
        }
        else
        {
          continue;
        }
      }
    default:
      if(query_strip_comments_is_white_space(current))
      {
        insert_space = true;
        ++query_position;
      }
      break; // make gcc happy
    }
    if(insert_space)
    {
      if((uint) (last_space + 1) != position)
      {
        last_space = position;
        buffer[position++] = ' ';
      }
    }
    else if (query_position < query.length)
    {
      buffer[position++] = query.str[query_position++];
    }
  }
  while((0 < position) && query_strip_comments_is_white_space(buffer[position - 1]))
  {
    --position;
  }
  buffer[position] = 0;
  length = position;
}
void QueryStripComments::cleanup()
{
  if(buffer)
  {
    my_free(buffer);
  }
  buffer        = 0;
  length        = 0;
  buffer_length = 0;
}

class QueryStripComments_Backup
{
public:
  QueryStripComments_Backup(THD* a_thd, QueryStripComments* qsc);
  ~QueryStripComments_Backup();
private:
  THD* thd;
  LEX_CSTRING query;
};

QueryStripComments_Backup::QueryStripComments_Backup(THD* a_thd,
                                                     QueryStripComments* qsc)
{
  if(opt_query_cache_strip_comments)
  {
    thd = a_thd;
    query = thd->query();
    qsc->set(query, QUERY_BUFFER_ADDITIONAL_LENGTH(thd->db().length));
    *(size_t *) (qsc->query() + qsc->query_length() + 1)= thd->db().length;
    thd->set_query(qsc->query(),qsc->query_length());
  }
  else
  {
    thd = 0;
    query.str = NULL;
    query.length = 0;
  }
}
QueryStripComments_Backup::~QueryStripComments_Backup()
{
  if(thd)
  {
    thd->set_query(query);
  }
}

#ifdef EMBEDDED_LIBRARY
#include "emb_qcache.h"
#endif

using std::min;
using std::max;

#if defined(EXTRA_DEBUG) && !defined(NDEBUG)
#define RW_WLOCK(M) {DBUG_PRINT("lock", ("rwlock wlock 0x%lx",(ulong)(M))); \
  if (!mysql_rwlock_wrlock(M)) DBUG_PRINT("lock", ("rwlock wlock ok")); \
  else DBUG_PRINT("lock", ("rwlock wlock FAILED %d", errno)); }
#define RW_RLOCK(M) {DBUG_PRINT("lock", ("rwlock rlock 0x%lx", (ulong)(M))); \
  if (!mysql_rwlock_rdlock(M)) DBUG_PRINT("lock", ("rwlock rlock ok")); \
  else DBUG_PRINT("lock", ("rwlock wlock FAILED %d", errno)); }
#define RW_UNLOCK(M) {DBUG_PRINT("lock", ("rwlock unlock 0x%lx",(ulong)(M))); \
  if (!mysql_rwlock_unlock(M)) DBUG_PRINT("lock", ("rwlock unlock ok")); \
  else DBUG_PRINT("lock", ("rwlock unlock FAILED %d", errno)); }
#define BLOCK_LOCK_WR(B) {DBUG_PRINT("lock", ("%d LOCK_WR 0x%lx",\
  __LINE__,(ulong)(B))); \
  B->query()->lock_writing();}
#define BLOCK_LOCK_RD(B) {DBUG_PRINT("lock", ("%d LOCK_RD 0x%lx",\
  __LINE__,(ulong)(B))); \
  B->query()->lock_reading();}
#define BLOCK_UNLOCK_WR(B) { \
  DBUG_PRINT("lock", ("%d UNLOCK_WR 0x%lx",\
  __LINE__,(ulong)(B)));B->query()->unlock_writing();}
#define BLOCK_UNLOCK_RD(B) { \
  DBUG_PRINT("lock", ("%d UNLOCK_RD 0x%lx",\
  __LINE__,(ulong)(B)));B->query()->unlock_reading();}
#define DUMP(C) DBUG_EXECUTE("qcache", {\
  (C)->cache_dump(); (C)->queries_dump();(C)->tables_dump();})
#else
#define RW_WLOCK(M) mysql_rwlock_wrlock(M)
#define RW_RLOCK(M) mysql_rwlock_rdlock(M)
#define RW_UNLOCK(M) mysql_rwlock_unlock(M)
#define BLOCK_LOCK_WR(B) B->query()->lock_writing()
#define BLOCK_LOCK_RD(B) B->query()->lock_reading()
#define BLOCK_UNLOCK_WR(B) B->query()->unlock_writing()
#define BLOCK_UNLOCK_RD(B) B->query()->unlock_reading()
#define DUMP(C)
#endif


/**
  Macro that executes the requested action at a synchronization point
  only if the thread has a associated THD session.
*/
#if defined(ENABLED_DEBUG_SYNC)
#define QC_DEBUG_SYNC(name)               \
  do {                                    \
    THD *thd= current_thd;                \
    if (thd)                              \
      DEBUG_SYNC(thd, name);              \
  } while (0)
#else
#define QC_DEBUG_SYNC(name)
#endif

// Max aligned size for ulong type query_cache_min_res_unit.
static const ulong max_aligned_min_res_unit_size= ((ULONG_MAX) &
                                                   (~(sizeof(double) - 1)));

/**
  Thread state to be used when the query cache lock needs to be acquired.
  Sets the thread state name in the constructor, resets on destructor.
*/

struct Query_cache_wait_state
{
  THD *m_thd;
  PSI_stage_info m_old_stage;
  const char *m_func;
  const char *m_file;
  int m_line;

  Query_cache_wait_state(THD *thd, const char *func,
                         const char *file, unsigned int line)
  : m_thd(thd),
    m_old_stage(),
    m_func(func), m_file(file), m_line(line)
  {
    if (m_thd)
      m_thd->enter_stage(&stage_waiting_for_query_cache_lock,
                         &m_old_stage,
                         m_func, m_file, m_line);
  }

  ~Query_cache_wait_state()
  {
    if (m_thd)
      m_thd->enter_stage(&m_old_stage, NULL, m_func, m_file, m_line);
  }
};


/**
   Construct the key used for cache lookup.
   The key is query + NULL + current DB (if any) + cache flags
   The key is allocated on THD's mem_root.

   @param thd              Thread context
   @param query            Query string
   @param flags            Cache query flags
   @param tot_length[out]  Length of the key

   @return The constructed cache key or NULL if OOM
*/

static char *make_cache_key(THD *thd,
                            const LEX_CSTRING &query,
                            Query_cache_query_flags *flags,
                            size_t *tot_length)
{
  *tot_length= query.length + 1 + thd->db().length + QUERY_CACHE_FLAGS_SIZE;
  char *cache_key= static_cast<char*>(thd->alloc(*tot_length));
  if (cache_key == NULL)
    return NULL;

  memcpy(cache_key, query.str, query.length);
  cache_key[query.length]= '\0';
  if (thd->db().length)
    memcpy(cache_key + query.length + 1, thd->db().str, thd->db().length);

  /*
    We should only copy structure (don't use it location directly)
    because of alignment issue
  */
  memcpy((void*) (cache_key + (*tot_length - QUERY_CACHE_FLAGS_SIZE)),
         flags, QUERY_CACHE_FLAGS_SIZE);
  return cache_key;
}


/**
  Serialize access to the query cache.
  If the lock cannot be granted the thread hangs in a conditional wait which
  is signalled on each unlock.

  The lock attempt will also fail without wait if lock_and_suspend() is in
  effect by another thread. This enables a quick path in execution to skip waits
  when the outcome is known.

  @param use_timeout TRUE if the lock can abort because of a timeout.

  @note use_timeout is optional and default value is FALSE.

  @return
   @retval FALSE An exclusive lock was taken
   @retval TRUE The locking attempt failed
*/

bool Query_cache::try_lock(bool use_timeout)
{
  bool interrupt= FALSE;
  THD *thd= current_thd;
  Query_cache_wait_state wait_state(thd, __func__, __FILE__, __LINE__);
  DBUG_ENTER("Query_cache::try_lock");

  const char* old_proc_info= thd->proc_info;
  thd_proc_info(thd,"Waiting on query cache mutex");
  DEBUG_SYNC(thd, "before_query_cache_mutex");
  mysql_mutex_lock(&structure_guard_mutex);
  DEBUG_SYNC(thd, "after_query_cache_mutex");
  thd->proc_info = old_proc_info;
  while (1)
  {
    if (m_cache_lock_status == Query_cache::UNLOCKED)
    {
      m_cache_lock_status= Query_cache::LOCKED;
#ifndef NDEBUG
      if (thd)
        m_cache_lock_thread_id= thd->thread_id();
#endif
      break;
    }
    else if (m_cache_lock_status == Query_cache::LOCKED_NO_WAIT)
    {
      /*
        If query cache is protected by a LOCKED_NO_WAIT lock this thread
        should avoid using the query cache as it is being evicted.
      */
      interrupt= TRUE;
      break;
    }
    else
    {
      assert(m_cache_lock_status == Query_cache::LOCKED);
      /*
        To prevent send_result_to_client() and query_cache_insert() from
        blocking execution for too long a timeout is put on the lock.
      */
      if (use_timeout)
      {
        struct timespec waittime;
        set_timespec_nsec(&waittime, 50000000UL);  /* Wait for 50 msec */
        int res= mysql_cond_timedwait(&COND_cache_status_changed,
                                      &structure_guard_mutex, &waittime);
        if (res == ETIMEDOUT)
        {
          interrupt= TRUE;
          break;
        }
      }
      else
      {
        mysql_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
      }
    }
  }
  mysql_mutex_unlock(&structure_guard_mutex);

  DBUG_RETURN(interrupt);
}


/**
  Serialize access to the query cache.
  If the lock cannot be granted the thread hangs in a conditional wait which
  is signalled on each unlock.

  This method also suspends the query cache so that other threads attempting to
  lock the cache with try_lock() will fail directly without waiting.

  It is used by all methods which flushes or destroys the whole cache.
 */

void Query_cache::lock_and_suspend(void)
{
  THD *thd= current_thd;
  Query_cache_wait_state wait_state(thd, __func__, __FILE__, __LINE__);
  DBUG_ENTER("Query_cache::lock_and_suspend");

  mysql_mutex_lock(&structure_guard_mutex);
  while (m_cache_lock_status != Query_cache::UNLOCKED)
    mysql_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
  m_cache_lock_status= Query_cache::LOCKED_NO_WAIT;
#ifndef NDEBUG
  if (thd)
    m_cache_lock_thread_id= thd->thread_id();
#endif
  /* Wake up everybody, a whole cache flush is starting! */
  mysql_cond_broadcast(&COND_cache_status_changed);
  mysql_mutex_unlock(&structure_guard_mutex);

  DBUG_VOID_RETURN;
}

/**
  Serialize access to the query cache.
  If the lock cannot be granted the thread hangs in a conditional wait which
  is signalled on each unlock.

  It is used by all methods which invalidates one or more tables.
 */

void Query_cache::lock(void)
{
  THD *thd= current_thd;
  Query_cache_wait_state wait_state(thd, __func__, __FILE__, __LINE__);
  DBUG_ENTER("Query_cache::lock");

  mysql_mutex_lock(&structure_guard_mutex);
  while (m_cache_lock_status != Query_cache::UNLOCKED)
    mysql_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
  m_cache_lock_status= Query_cache::LOCKED;
#ifndef NDEBUG
  if (thd)
    m_cache_lock_thread_id= thd->thread_id();
#endif
  mysql_mutex_unlock(&structure_guard_mutex);

  DBUG_VOID_RETURN;
}


/**
  Set the query cache to UNLOCKED and signal waiting threads.
*/

void Query_cache::unlock(void)
{
  DBUG_ENTER("Query_cache::unlock");
  mysql_mutex_lock(&structure_guard_mutex);
#ifndef NDEBUG
  THD *thd= current_thd;
  if (thd)
    assert(m_cache_lock_thread_id == thd->thread_id());
#endif
  assert(m_cache_lock_status == Query_cache::LOCKED ||
         m_cache_lock_status == Query_cache::LOCKED_NO_WAIT);
  m_cache_lock_status= Query_cache::UNLOCKED;
  DBUG_PRINT("Query_cache",("Sending signal"));
  mysql_cond_signal(&COND_cache_status_changed);
  mysql_mutex_unlock(&structure_guard_mutex);
  DBUG_VOID_RETURN;
}


/**
  Helper function for determine if a SELECT statement has a SQL_NO_CACHE
  directive.

  @param sql           Query string
  @param offset        Offset of the first whitespace character after SELECT
  @param query_length  The total length of the query string

  @return
   @retval TRUE The character string contains SQL_NO_CACHE
   @retval FALSE No directive found.
*/

static bool has_no_cache_directive(const char *sql, uint offset,
                                   size_t query_length)
{
  uint i= offset;

  // Must have at least one whitespace char before SQL_NO_CACHE
  if (!my_isspace(system_charset_info, sql[i]))
    return false;

  // But can have several
  while (i < query_length &&
         my_isspace(system_charset_info, sql[i]))
    ++i;

  // Check that we have enough chars left for SQL_NO_CACHE
  if (i + 12 >= query_length)
    return false;

  if (my_toupper(system_charset_info, sql[i])    == 'S' &&
      my_toupper(system_charset_info, sql[i+1])  == 'Q' &&
      my_toupper(system_charset_info, sql[i+2])  == 'L' &&
      my_toupper(system_charset_info, sql[i+3])  == '_' &&
      my_toupper(system_charset_info, sql[i+4])  == 'N' &&
      my_toupper(system_charset_info, sql[i+5])  == 'O' &&
      my_toupper(system_charset_info, sql[i+6])  == '_' &&
      my_toupper(system_charset_info, sql[i+7])  == 'C' &&
      my_toupper(system_charset_info, sql[i+8])  == 'A' &&
      my_toupper(system_charset_info, sql[i+9])  == 'C' &&
      my_toupper(system_charset_info, sql[i+10]) == 'H' &&
      my_toupper(system_charset_info, sql[i+11]) == 'E' &&
      my_isspace(system_charset_info, sql[i+12]))
    return true;

  return false;
}


/*****************************************************************************
 Query_cache_block_table method(s)
*****************************************************************************/

inline Query_cache_block * Query_cache_block_table::block()
{
  return (Query_cache_block *)(((uchar*)this) -
			       ALIGN_SIZE(sizeof(Query_cache_block_table)*n) -
			       ALIGN_SIZE(sizeof(Query_cache_block)));
}

/*****************************************************************************
   Query_cache_block method(s)
*****************************************************************************/

void Query_cache_block::init(ulong block_length)
{
  DBUG_ENTER("Query_cache_block::init");
  DBUG_PRINT("qcache", ("init block: 0x%lx  length: %lu", (ulong) this,
			block_length));
  length = block_length;
  used = 0;
  type = Query_cache_block::FREE;
  n_tables = 0;
  DBUG_VOID_RETURN;
}

void Query_cache_block::destroy()
{
  DBUG_ENTER("Query_cache_block::destroy");
  DBUG_PRINT("qcache", ("destroy block 0x%lx, type %d",
			(ulong) this, type));
  type = INCOMPLETE;
  DBUG_VOID_RETURN;
}

inline uint Query_cache_block::headers_len()
{
  return (ALIGN_SIZE(sizeof(Query_cache_block_table)*n_tables) +
	  ALIGN_SIZE(sizeof(Query_cache_block)));
}

inline uchar* Query_cache_block::data(void)
{
  return (uchar*)( ((uchar*)this) + headers_len() );
}

inline Query_cache_query * Query_cache_block::query()
{
#ifndef NDEBUG
  if (type != QUERY)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_query *) data();
}

inline Query_cache_table * Query_cache_block::table()
{
#ifndef NDEBUG
  if (type != TABLE)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_table *) data();
}

inline Query_cache_result * Query_cache_block::result()
{
#ifndef NDEBUG
  if (type != RESULT && type != RES_CONT && type != RES_BEG &&
      type != RES_INCOMPLETE)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_result *) data();
}

inline Query_cache_block_table * Query_cache_block::table(TABLE_COUNTER_TYPE n)
{
  return ((Query_cache_block_table *)
	  (((uchar*)this)+ALIGN_SIZE(sizeof(Query_cache_block)) +
	   n*sizeof(Query_cache_block_table)));
}


/*****************************************************************************
 *   Query_cache_table method(s)
 *****************************************************************************/

extern "C"
{
uchar *query_cache_table_get_key(const uchar *record, size_t *length,
				my_bool not_used MY_ATTRIBUTE((unused)))
{
  Query_cache_block* table_block = (Query_cache_block*) record;
  *length = (table_block->used - table_block->headers_len() -
	     ALIGN_SIZE(sizeof(Query_cache_table)));
  return (table_block->data() +
	  ALIGN_SIZE(sizeof(Query_cache_table)));
}
}

/*****************************************************************************
    Query_cache_query methods
*****************************************************************************/

/*
   Following methods work for block read/write locking only in this
   particular case and in interaction with structure_guard_mutex.

   Lock for write prevents any other locking. (exclusive use)
   Lock for read prevents only locking for write.
*/

inline void Query_cache_query::lock_writing()
{
  RW_WLOCK(&lock);
}


/*
  Needed for finding queries, that we may delete from cache.
  We don't want to wait while block become unlocked. In addition,
  block locking means that query is now used and we don't need to
  remove it.
*/

my_bool Query_cache_query::try_lock_writing()
{
  DBUG_ENTER("Query_cache_block::try_lock_writing");
  if (mysql_rwlock_trywrlock(&lock) != 0)
  {
    DBUG_PRINT("info", ("can't lock rwlock"));
    DBUG_RETURN(0);
  }
  DBUG_PRINT("info", ("rwlock 0x%lx locked", (ulong) &lock));
  DBUG_RETURN(1);
}


inline void Query_cache_query::lock_reading()
{
  RW_RLOCK(&lock);
}


inline void Query_cache_query::unlock_writing()
{
  RW_UNLOCK(&lock);
}


inline void Query_cache_query::unlock_reading()
{
  RW_UNLOCK(&lock);
}


void Query_cache_query::init_n_lock()
{
  DBUG_ENTER("Query_cache_query::init_n_lock");
  res=0; wri = 0; len = 0;
  mysql_rwlock_init(key_rwlock_query_cache_query_lock, &lock);
  lock_writing();
  DBUG_PRINT("qcache", ("inited & locked query for block 0x%lx",
			(long) (((uchar*) this) -
                                ALIGN_SIZE(sizeof(Query_cache_block)))));
  DBUG_VOID_RETURN;
}


void Query_cache_query::unlock_n_destroy()
{
  DBUG_ENTER("Query_cache_query::unlock_n_destroy");
  DBUG_PRINT("qcache", ("destroyed & unlocked query for block 0x%lx",
			(long) (((uchar*) this) -
                                ALIGN_SIZE(sizeof(Query_cache_block)))));
  /*
    The following call is not needed on system where one can destroy an
    active semaphore
  */
  this->unlock_writing();
  mysql_rwlock_destroy(&lock);
  DBUG_VOID_RETURN;
}


extern "C"
{
uchar *query_cache_query_get_key(const uchar *record, size_t *length,
				my_bool not_used)
{
  Query_cache_block *query_block = (Query_cache_block*) record;
  *length = (query_block->used - query_block->headers_len() -
	     ALIGN_SIZE(sizeof(Query_cache_query)));
  return (query_block->data() +
	  ALIGN_SIZE(sizeof(Query_cache_query)));
}
}

/*****************************************************************************
  Functions to store things into the query cache
*****************************************************************************/

/*
  Note on double-check locking (DCL) usage.

  Below, in query_cache_insert(), query_cache_abort() and
  Query_cache::end_of_result() we use what is called double-check
  locking (DCL) for Query_cache_tls::first_query_block.
  I.e. we test it first without a lock, and, if positive, test again
  under the lock.

  This means that if we see 'first_query_block == 0' without a
  lock we will skip the operation.  But this is safe here: when we
  started to cache a query, we called Query_cache::store_query(), and
  'first_query_block' was set to non-zero in this thread (and the
  thread always sees results of its memory operations, mutex or not).
  If later we see 'first_query_block == 0' without locking a
  mutex, that may only mean that some other thread have reset it by
  invalidating the query.  Skipping the operation in this case is the
  right thing to do, as first_query_block won't get non-zero for
  this query again.

  See also comments in Query_cache::store_query() and
  Query_cache::send_result_to_client().

  NOTE, however, that double-check locking is not applicable in
  'invalidate' functions, as we may erroneously skip invalidation,
  because the thread doing invalidation may never see non-zero
  'first_query_block'.
*/


/**
  libmysql convenience wrapper to insert data into query cache.
*/
void query_cache_insert(const char *packet, ulong length,
                        unsigned pkt_nr)
{
  THD *thd= current_thd;

  /*
    Current_thd can be NULL when a new connection is immediately ended
    due to "Too many connections". thd->store_globals() has not been
    called at this time and hence my_thread_setspecific_ptr(THR_THD,
    this) has not been called for this thread.
  */

  if (!thd)
    return;

  query_cache.insert(&thd->query_cache_tls,
                     packet, length,
                     pkt_nr);
}


/**
  Insert the packet into the query cache.
*/

void
Query_cache::insert(Query_cache_tls *query_cache_tls,
                    const char *packet, ulong length,
                    unsigned pkt_nr)
{
  DBUG_ENTER("Query_cache::insert");

  /* See the comment on double-check locking usage above. */
  if (is_disabled() || query_cache_tls->first_query_block == NULL)
    DBUG_VOID_RETURN;

  QC_DEBUG_SYNC("wait_in_query_cache_insert");

  if (try_lock())
    DBUG_VOID_RETURN;

  Query_cache_block *query_block = query_cache_tls->first_query_block;
  if (query_block == NULL)
  {
    /*
      We lost the writer and the currently processed query has been
      invalidated; there is nothing left to do.
    */
    unlock();
    DBUG_VOID_RETURN;
  }
  BLOCK_LOCK_WR(query_block);
  Query_cache_query *header= query_block->query();
  Query_cache_block *result= header->result();

  DUMP(this);
  DBUG_PRINT("qcache", ("insert packet %lu bytes long",length));

  /*
    On success, STRUCT_UNLOCK is done by append_result_data. Otherwise, we
    still need structure_guard_mutex to free the query, and therefore unlock
    it later in this function.
  */
  if (!append_result_data(&result, length, (uchar*) packet,
                          query_block))
  {
    DBUG_PRINT("warning", ("Can't append data"));
    header->result(result);
    DBUG_PRINT("qcache", ("free query 0x%lx", (ulong) query_block));
    // The following call will remove the lock on query_block
    query_cache.free_query(query_block);
    query_cache.refused++;
    // append_result_data no success => we need unlock
    unlock();
    DBUG_VOID_RETURN;
  }

  header->result(result);
  header->last_pkt_nr= pkt_nr;
  BLOCK_UNLOCK_WR(query_block);

  DBUG_EXECUTE("check_querycache", check_integrity(LOCK_WHILE_CHECKING););

  DBUG_VOID_RETURN;
}


void
Query_cache::abort(Query_cache_tls *query_cache_tls)
{
  DBUG_ENTER("query_cache_abort");
  THD *thd= current_thd;

  /* See the comment on double-check locking usage above. */
  if (is_disabled() || query_cache_tls->first_query_block == NULL)
    DBUG_VOID_RETURN;

  if (try_lock())
    DBUG_VOID_RETURN;

  /*
    While we were waiting another thread might have changed the status
    of the writer. Make sure the writer still exists before continue.
  */
  Query_cache_block *query_block= query_cache_tls->first_query_block;
  if (query_block)
  {
    THD_STAGE_INFO(thd, stage_storing_result_in_query_cache);
    DUMP(this);
    BLOCK_LOCK_WR(query_block);
    // The following call will remove the lock on query_block
    free_query(query_block);
    query_cache_tls->first_query_block= NULL;
    DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););
  }

  unlock();

  DBUG_VOID_RETURN;
}


void Query_cache::end_of_result(THD *thd)
{
  Query_cache_block *query_block;
  Query_cache_tls *query_cache_tls= &thd->query_cache_tls;
  ulonglong current_found_rows= thd->current_found_rows;
  DBUG_ENTER("Query_cache::end_of_result");

  /* See the comment on double-check locking usage above. */
  if (query_cache_tls->first_query_block == NULL)
    DBUG_VOID_RETURN;

  if (thd->killed || thd->is_error())
  {
    abort(&thd->query_cache_tls);
    DBUG_VOID_RETURN;
  }

  /* Ensure that only complete results are cached. */
  assert(thd->get_stmt_da()->is_eof());

#ifdef EMBEDDED_LIBRARY
  insert(query_cache_tls, (char*)thd,
                     emb_count_querycache_size(thd), 0);
#endif

  if (try_lock())
    DBUG_VOID_RETURN;

  query_block= query_cache_tls->first_query_block;
  if (query_block)
  {
    /*
      The writer is still present; finish last result block by chopping it to
      suitable size if needed and setting block type. Since this is the last
      block, the writer should be dropped.
    */
    THD_STAGE_INFO(thd, stage_storing_result_in_query_cache);
    DUMP(this);
    BLOCK_LOCK_WR(query_block);
    Query_cache_query *header= query_block->query();
    Query_cache_block *last_result_block;
    ulong allign_size;
    ulong len;

    if (header->result() == 0)
    {
      DBUG_PRINT("error", ("End of data with no result blocks; "
                           "Query '%s' removed from cache.", header->query()));
      /*
        Extra safety: empty result should not happen in the normal call
        to this function. In the release version that query should be ignored
        and removed from QC.
      */
      assert(0);
      free_query(query_block);
      unlock();
      DBUG_VOID_RETURN;
    }
    last_result_block= header->result()->prev;
    allign_size= ALIGN_SIZE(last_result_block->used);
    len= max(query_cache.min_allocation_unit, allign_size);
    if (last_result_block->length >= query_cache.min_allocation_unit + len)
      query_cache.split_block(last_result_block,len);

    header->found_rows(current_found_rows);
    header->result()->type= Query_cache_block::RESULT;

    /* Drop the writer. */
    header->writer(0);
    query_cache_tls->first_query_block= NULL;
    BLOCK_UNLOCK_WR(query_block);
    DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););
  }

  unlock();
  DBUG_VOID_RETURN;
}

void query_cache_invalidate_by_MyISAM_filename(const char *filename)
{
  query_cache.invalidate_by_MyISAM_filename(filename);
}


/**
  This is a convenience function used by the innodb plugin.
*/
extern "C"
void mysql_query_cache_invalidate4(THD *thd,
                                   const char *key, unsigned key_length,
                                   int using_trx)
{
  char qcache_key_name[2 * (NAME_LEN + 1)];
  char db_name[NAME_CHAR_LEN * FILENAME_CHARSET_MBMAXLEN + 1];
  const char *key_ptr;
  size_t tabname_len, dbname_len;

  // Extract the database name.
  key_ptr= strchr(key, '/');
  memcpy(db_name, key, (key_ptr - key));
  db_name[(key_ptr - key)]= '\0';

  /*
    Construct the key("db@002dname\0table@0024name\0") in a canonical format for
    the query cache using the key("db-name\0table$name\0") which is
    in its non-canonical form.
  */
  dbname_len= filename_to_tablename(db_name, qcache_key_name,
                                    sizeof(qcache_key_name));
  tabname_len= filename_to_tablename(++key_ptr,
                                     (qcache_key_name + dbname_len + 1),
                                     sizeof(qcache_key_name) - dbname_len - 1);

  query_cache.invalidate(thd, qcache_key_name, (dbname_len + tabname_len + 2),
                         (my_bool) using_trx);
}


/*****************************************************************************
   Query_cache methods
*****************************************************************************/

Query_cache::Query_cache(ulong query_cache_limit_arg,
			 ulong min_allocation_unit_arg,
			 ulong min_result_data_size_arg,
			 uint def_query_hash_size_arg,
			 uint def_table_hash_size_arg)
  :query_cache_size(0),
   query_cache_limit(query_cache_limit_arg),
   queries_in_cache(0), hits(0), inserts(0), refused(0),
   total_blocks(0), lowmem_prunes(0), m_query_cache_is_disabled(FALSE),
   min_allocation_unit(ALIGN_SIZE(min_allocation_unit_arg)),
   min_result_data_size(ALIGN_SIZE(min_result_data_size_arg)),
   def_query_hash_size(ALIGN_SIZE(def_query_hash_size_arg)),
   def_table_hash_size(ALIGN_SIZE(def_table_hash_size_arg)),
   initialized(0)
{
  ulong min_needed= (ALIGN_SIZE(sizeof(Query_cache_block)) +
		     ALIGN_SIZE(sizeof(Query_cache_block_table)) +
		     ALIGN_SIZE(sizeof(Query_cache_query)) + 3);
  set_if_bigger(min_allocation_unit,min_needed);
  this->min_allocation_unit= ALIGN_SIZE(min_allocation_unit);
  set_if_bigger(this->min_result_data_size,min_allocation_unit);
}


ulong Query_cache::resize(ulong query_cache_size_arg)
{
  ulong new_query_cache_size;
  DBUG_ENTER("Query_cache::resize");
  DBUG_PRINT("qcache", ("from %lu to %lu",query_cache_size,
			query_cache_size_arg));
  assert(initialized);

  lock_and_suspend();

  /*
    Wait for all readers and writers to exit. When the list of all queries
    is iterated over with a block level lock, we are done.
  */
  Query_cache_block *block= queries_blocks;
  if (block)
  {
    do
    {
      BLOCK_LOCK_WR(block);
      Query_cache_query *query= block->query();
      if (query->writer())
      {
        /*
           Drop the writer; this will cancel any attempts to store
           the processed statement associated with this writer.
         */
        query->writer()->first_query_block= NULL;
        query->writer(0);
        refused++;
      }
      query->unlock_n_destroy();
      block= block->next;
    } while (block != queries_blocks);
  }
  free_cache();

  query_cache_size= query_cache_size_arg;
  new_query_cache_size= init_cache();

  if (new_query_cache_size)
    DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););

  unlock();
  DBUG_RETURN(new_query_cache_size);
}


ulong Query_cache::set_min_res_unit(ulong size)
{
  if (size < min_allocation_unit)
    size= min_allocation_unit;
  else if (size > max_aligned_min_res_unit_size)
    size= max_aligned_min_res_unit_size;

  return (min_result_data_size= ALIGN_SIZE(size));
}


void Query_cache::store_query(THD *thd, TABLE_LIST *tables_used)
{
  TABLE_COUNTER_TYPE local_tables;
  DBUG_ENTER("Query_cache::store_query");
  /*
    Testing 'query_cache_size' without a lock here is safe: the thing
    we may loose is that the query won't be cached, but we save on
    mutex locking in the case when query cache is disabled or the
    query is uncachable.

    See also a note on double-check locking usage above.
  */
  if (thd->locked_tables_mode || query_cache_size == 0)
    DBUG_VOID_RETURN;

  /*
    Do not store queries while tracking transaction state.
    The tracker already flags queries that actually have
    transaction tracker items, but this will make behavior
    more straight forward.
  */
  if (thd->variables.session_track_transaction_info != TX_TRACK_NONE)
    DBUG_VOID_RETURN;

  /*
    The query cache is only supported for the classic protocols.
    Although protocol_callback.cc is not compiled in embedded, there
    are other protocols. A check outside the non-embedded block is
    better.
  */
  if (!thd->is_classic_protocol())
    DBUG_VOID_RETURN;
#ifndef EMBEDDED_LIBRARY
  /*
    Without active vio, net_write_packet() will not be called and
    therefore neither Query_cache::insert(). Since we will never get a
    complete query result in this case, it does not make sense to
    register the query in the first place.
  */
  if (!thd->get_protocol()->connection_alive())
    DBUG_VOID_RETURN;
#endif

  uint8 tables_type= 0;

  if ((local_tables= is_cacheable(thd, thd->lex, tables_used, &tables_type)))
  {
    Query_cache_query_flags flags;
    // fill all gaps between fields with 0 to get repeatable key
    memset(&flags, 0, QUERY_CACHE_FLAGS_SIZE);
    flags.client_long_flag=
      thd->get_protocol()->has_client_capability(CLIENT_LONG_FLAG);
    flags.client_protocol_41=
      thd->get_protocol()->has_client_capability(CLIENT_PROTOCOL_41);
    /*
      Protocol influences result format, so statement results in the binary
      protocol (COM_EXECUTE) cannot be served to statements asking for results
      in the text protocol (COM_QUERY) and vice-versa.
    */
    flags.protocol_type= (unsigned int) thd->get_protocol()->type();
    /* PROTOCOL_LOCAL results are not cached. */
    assert(flags.protocol_type != (unsigned int) Protocol::PROTOCOL_LOCAL);
    flags.more_results_exists= MY_TEST(thd->server_status &
                                       SERVER_MORE_RESULTS_EXISTS);
    flags.in_trans= thd->in_active_multi_stmt_transaction();
    flags.autocommit= MY_TEST(thd->server_status & SERVER_STATUS_AUTOCOMMIT);
    flags.pkt_nr= thd->get_protocol_classic()->get_pkt_nr();
    flags.character_set_client_num=
      thd->variables.character_set_client->number;
    flags.character_set_results_num=
      (thd->variables.character_set_results ?
       thd->variables.character_set_results->number :
       UINT_MAX);
    flags.collation_connection_num=
      thd->variables.collation_connection->number;
    flags.limit= thd->variables.select_limit;
    flags.time_zone= thd->variables.time_zone;
    flags.sql_mode= thd->variables.sql_mode;
    flags.max_sort_length= thd->variables.max_sort_length;
    flags.lc_time_names= thd->variables.lc_time_names;
    flags.group_concat_max_len= thd->variables.group_concat_max_len;
    flags.div_precision_increment= thd->variables.div_precincrement;
    flags.default_week_format= thd->variables.default_week_format;
    DBUG_PRINT("qcache", ("\
long %d, 4.1: %d, bin_proto: %d, more results %d, pkt_nr: %d, \
CS client: %u, CS result: %u, CS conn: %u, limit: %lu, TZ: 0x%lx, \
sql mode: 0x%llx, sort len: %lu, conncat len: %lu, div_precision: %lu, \
def_week_frmt: %lu, in_trans: %d, autocommit: %d",
                          (int)flags.client_long_flag,
                          (int)flags.client_protocol_41,
                          (int)flags.protocol_type,
                          (int)flags.more_results_exists,
                          flags.pkt_nr,
                          flags.character_set_client_num,
                          flags.character_set_results_num,
                          flags.collation_connection_num,
                          (ulong) flags.limit,
                          (ulong) flags.time_zone,
                          flags.sql_mode,
                          flags.max_sort_length,
                          flags.group_concat_max_len,
                          flags.div_precision_increment,
                          flags.default_week_format,
                          (int)flags.in_trans,
                          (int)flags.autocommit));

    /*
     Make InnoDB to release the adaptive hash index latch before
     acquiring the query cache mutex.
    */
    ha_release_temporary_latches(thd);

    /*
      A table- or a full flush operation can potentially take a long time to
      finish. We choose not to wait for them and skip caching statements
      instead.

      In case the wait time can't be determined there is an upper limit which
      causes try_lock() to abort with a time out.

      The 'TRUE' parameter indicate that the lock is allowed to timeout

    */
    if (try_lock(TRUE))
      DBUG_VOID_RETURN;
    if (query_cache_size == 0)
    {
      unlock();
      DBUG_VOID_RETURN;
    }
    DUMP(this);

    if (ask_handler_allowance(thd, tables_used))
    {
      refused++;
      unlock();
      DBUG_VOID_RETURN;
    }
    QueryStripComments *query_strip_comments = &(thd->query_strip_comments);
    QueryStripComments_Backup backup(thd,query_strip_comments);

    /* Key is query + database + flag */
    size_t tot_length;
    char *cache_key= make_cache_key(thd, thd->query(), &flags, &tot_length);
    if (cache_key == NULL)
    {
      unlock();
      DBUG_VOID_RETURN;
    }

    /* Check if another thread is processing the same query? */
    Query_cache_block *competitor = (Query_cache_block *)
      my_hash_search(&queries, (uchar*) cache_key, tot_length);
    DBUG_PRINT("qcache", ("competitor 0x%lx", (ulong) competitor));
    if (competitor == 0)
    {
      /* Query is not in cache and no one is working with it; Store it */
      Query_cache_block *query_block;
      query_block= write_block_data(tot_length, (uchar*) cache_key,
				    ALIGN_SIZE(sizeof(Query_cache_query)),
				    Query_cache_block::QUERY, local_tables);
      if (query_block != 0)
      {
	DBUG_PRINT("qcache", ("query block 0x%lx allocated, %lu",
			    (ulong) query_block, query_block->used));

	Query_cache_query *header = query_block->query();
	header->init_n_lock();
	if (my_hash_insert(&queries, (uchar*) query_block))
	{
	  refused++;
	  DBUG_PRINT("qcache", ("insertion in query hash"));
	  header->unlock_n_destroy();
	  free_memory_block(query_block);
          unlock();
	  goto end;
	}
	if (!register_all_tables(query_block, tables_used, local_tables))
	{
	  refused++;
	  DBUG_PRINT("warning", ("tables list including failed"));
	  my_hash_delete(&queries, (uchar *) query_block);
	  header->unlock_n_destroy();
	  free_memory_block(query_block);

          unlock();
	  goto end;
	}
	double_linked_list_simple_include(query_block, &queries_blocks);
	inserts++;
	queries_in_cache++;
	thd->query_cache_tls.first_query_block= query_block;
	header->writer(&thd->query_cache_tls);
	header->tables_type(tables_type);
        unlock();

	// init_n_lock make query block locked
	BLOCK_UNLOCK_WR(query_block);
      }
      else
      {
	// We have not enough memory to store query => do nothing
	refused++;
        unlock();
	DBUG_PRINT("warning", ("Can't allocate query"));
      }
    }
    else
    {
      // Another thread is processing the same query => do nothing
      refused++;
      unlock();
      DBUG_PRINT("qcache", ("Another thread process same query"));
    }
  }
  else if (thd->lex->sql_command == SQLCOM_SELECT)
    refused++;

end:
  DBUG_VOID_RETURN;
}


#ifndef EMBEDDED_LIBRARY
/**
  Send a single memory block from the query cache.

  Respects the client/server protocol limits for the
  size of the network packet, and splits a large block
  in pieces to ensure that individual piece doesn't exceed
  the maximal allowed size of the network packet (16M).

  @param[in] net NET handler
  @param[in] packet packet to send
  @param[in] len packet length

  @return Operation status
    @retval FALSE On success
    @retval TRUE On error
*/
static bool
send_data_in_chunks(NET *net, const uchar *packet, ulong len)
{
  /*
    On the client we may require more memory than max_allowed_packet
    to keep, both, the truncated last logical packet, and the
    compressed next packet.  This never (or in practice never)
    happens without compression, since without compression it's very
    unlikely that a) a truncated logical packet would remain on the
    client when it's time to read the next packet b) a subsequent
    logical packet that is being read would be so large that
    size-of-new-packet + size-of-old-packet-tail >
    max_allowed_packet.  To remedy this issue, we send data in 1MB
    sized packets, that's below the current client default of 16MB
    for max_allowed_packet, but large enough to ensure there is no
    unnecessary overhead from too many syscalls per result set.
  */
  static const ulong MAX_CHUNK_LENGTH= 1024*1024;

  while (len > MAX_CHUNK_LENGTH)
  {
    if (net_write_packet(net, packet, MAX_CHUNK_LENGTH))
      return TRUE;
    packet+= MAX_CHUNK_LENGTH;
    len-= MAX_CHUNK_LENGTH;
  }
  if (len && net_write_packet(net, packet, len))
    return TRUE;

  return FALSE;
}
#endif


/*
  Check if the query is in the cache. If it was cached, send it
  to the user.

  @param thd Pointer to the thread handler
  @param sql A reference to the sql statement *

  @return status code
  @retval 0  Query was not cached.
  @retval 1  The query was cached and user was sent the result.
  @retval -1 The query was cached but we didn't have rights to use it.

  In case of -1, no error is sent to the client.

  *) The buffer must be allocated memory of size:
  tot_length= query_length + thd->db_length + 1 + QUERY_CACHE_FLAGS_SIZE;
*/

int Query_cache::send_result_to_client(THD *thd, const LEX_CSTRING &sql)
{
  ulonglong engine_data;
  Query_cache_query *query;
#ifndef EMBEDDED_LIBRARY
  Query_cache_block *first_result_block;
#endif
  Query_cache_block *result_block;
  Query_cache_block_table *block_table, *block_table_end;
  char *cache_key= NULL;
  size_t tot_length;
  Query_cache_query_flags flags;
  QueryStripComments *query_strip_comments = &(thd->query_strip_comments);
  DBUG_ENTER("Query_cache::send_result_to_client");

  /*
    Testing 'query_cache_size' without a lock here is safe: the thing
    we may loose is that the query won't be served from cache, but we
    save on mutex locking in the case when query cache is disabled.

    See also a note on double-check locking usage above.
  */
  if (is_disabled() || thd->locked_tables_mode ||
      thd->variables.query_cache_type == 0 || query_cache_size == 0)
    goto err;

  /*
    Don't work with Query_cache if the state of XA transaction is
    either IDLE or PREPARED. If we didn't do so we would get an
    assert fired later in the function trx_start_if_not_started_low()
    that is called when we are checking that query cache is allowed at
    this moment to operate on an InnoDB table.
  */
  if (thd->get_transaction()->xid_state()->check_xa_idle_or_prepared(false))
    goto err;

  /*
    Don't allow serving from Query_cache while tracking transaction
    state. This is a safeguard in case an otherwise matching query
    was added to the cache before tracking was turned on.
  */
  if (thd->variables.session_track_transaction_info != TX_TRACK_NONE)
    goto err;

  if (!thd->lex->safe_to_cache_query)
  {
    DBUG_PRINT("qcache", ("SELECT is non-cacheable"));
    goto err;
  }

  {
    uint i= 0;
    if(opt_query_cache_strip_comments)
    {
      /* Skip all comments and non-letter symbols */
      uint& query_position = i;
      const char* query = sql.str;
      while(query_position < sql.length)
      {
        bool check = false;
        char current = query[query_position];
        switch(current)
        {
        case '/':
          if (((query_position + 2) < sql.length)
              && ('*' == query[query_position+1])
              && ('!' != query[query_position+2]))
          {
            query_position += 2; // skip "/*"
            do
            {
              if('*' == query[query_position] && '/' == query[query_position+1]) // check for "*/" (without space)
              {
                query_position += 2; // skip "*/" (without space)
                break;
              }
              else
              {
                ++query_position;
              }
            }
            while (query_position < sql.length);
            continue; // analyze current symbol
          }
          break;
        case '-':
          if(query[query_position+1] == '-')
          {
            ++query_position; // skip "-"
          }
          else
          {
            break;
          }
          // fallthrough
        case '#':
          do
          {
            ++query_position; // skip current symbol
            if('\n' == query[query_position])  // check for '\n'
            {
              ++query_position; // skip '\n'
              break;
            }
          }
          while (query_position < sql.length);
          continue; // analyze current symbol
        case '\r':
        case '\n':
        case '\t':
        case ' ':
        case '(':
        case ')':
          break;
        default:
          check = true;
          break; // make gcc happy
        } // switch(current)
        if(check)
        {
          if (query_position + 2 < sql.length)
          {
            // cacheable
            break;
          }
          else
          {
            DBUG_PRINT("qcache", ("The statement is not a SELECT; Not cached"));
            goto err;
          }
        } // if(check)
        ++query_position;
      } // while(query_position < query_length)
    }
    else // if(opt_query_cache_strip_comments)
    {
      /*
        Skip '(' characters in queries like following:
        (select a from t1) union (select a from t1);
      */
      while (sql.str[i]=='(')
        i++;

    } // if(opt_query_cache_strip_comments)
      /*
        Test if the query is a SELECT
        (pre-space is removed in dispatch_command).

        First '/' looks like comment before command it is not
        frequently appeared in real life, consequently we can
        check all such queries, too.
      */
    if ((my_toupper(system_charset_info, sql.str[i])     != 'S' ||
         my_toupper(system_charset_info, sql.str[i + 1]) != 'E' ||
         my_toupper(system_charset_info, sql.str[i + 2]) != 'L' ||
         my_toupper(system_charset_info, sql.str[i + 3]) != 'E' ||
         my_toupper(system_charset_info, sql.str[i + 4]) != 'C' ||
         my_toupper(system_charset_info, sql.str[i + 5]) != 'T') &&
        (sql.str[i] != '/' || sql.length < i+6))
    {
      DBUG_PRINT("qcache", ("The statement is not a SELECT; Not cached"));
      goto err;
    }

    DBUG_EXECUTE_IF("test_sql_no_cache",
                    assert(has_no_cache_directive(sql.str, i+6,
                                                  sql.length)););
    if (has_no_cache_directive(sql.str, i+6, sql.length))
    {
      /*
        We do not increase 'refused' statistics here since it will be done
        later when the query is parsed.
      */
      DBUG_PRINT("qcache", ("The statement has a SQL_NO_CACHE directive"));
      goto err;
    }
  }
  /*
    Try to obtain an exclusive lock on the query cache. If the cache is
    disabled or if a full cache flush is in progress, the attempt to
    get the lock is aborted.

    The 'TRUE' parameter indicate that the lock is allowed to timeout
  */
  if (try_lock(TRUE))
    goto err;

  if (query_cache_size == 0)
    goto err_unlock;

  Query_cache_block *query_block;
  LEX_CSTRING stripped_query;
  if(opt_query_cache_strip_comments)
  {
    query_strip_comments->set(sql, // TODO remove additional length
                              QUERY_BUFFER_ADDITIONAL_LENGTH(
                                                    thd->db().length));
    stripped_query.str= query_strip_comments->query();
    stripped_query.length= query_strip_comments->query_length();
  }

  THD_STAGE_INFO(thd, stage_checking_query_cache_for_query);

  // fill all gaps between fields with 0 to get repeatable key
  memset(&flags, 0, QUERY_CACHE_FLAGS_SIZE);
  flags.client_long_flag= MY_TEST(
    thd->get_protocol()->has_client_capability(CLIENT_LONG_FLAG));
  flags.client_protocol_41= MY_TEST(
    thd->get_protocol()->has_client_capability(CLIENT_PROTOCOL_41));
  flags.protocol_type= (unsigned int) thd->get_protocol()->type();
  flags.more_results_exists= MY_TEST(thd->server_status &
                                     SERVER_MORE_RESULTS_EXISTS);
  flags.in_trans= thd->in_active_multi_stmt_transaction();
  flags.autocommit= MY_TEST(thd->server_status & SERVER_STATUS_AUTOCOMMIT);
  flags.pkt_nr= thd->get_protocol_classic()->get_pkt_nr();
  flags.character_set_client_num= thd->variables.character_set_client->number;
  flags.character_set_results_num=
    (thd->variables.character_set_results ?
     thd->variables.character_set_results->number :
     UINT_MAX);
  flags.collation_connection_num= thd->variables.collation_connection->number;
  flags.limit= thd->variables.select_limit;
  flags.time_zone= thd->variables.time_zone;
  flags.sql_mode= thd->variables.sql_mode;
  flags.max_sort_length= thd->variables.max_sort_length;
  flags.group_concat_max_len= thd->variables.group_concat_max_len;
  flags.div_precision_increment= thd->variables.div_precincrement;
  flags.default_week_format= thd->variables.default_week_format;
  flags.lc_time_names= thd->variables.lc_time_names;
  DBUG_PRINT("qcache", ("\
long %d, 4.1: %d, bin_proto: %d, more results %d, pkt_nr: %d, \
CS client: %u, CS result: %u, CS conn: %u, limit: %lu, TZ: 0x%lx, \
sql mode: 0x%llx, sort len: %lu, conncat len: %lu, div_precision: %lu, \
def_week_frmt: %lu, in_trans: %d, autocommit: %d",
                          (int)flags.client_long_flag,
                          (int)flags.client_protocol_41,
                          (int)flags.protocol_type,
                          (int)flags.more_results_exists,
                          flags.pkt_nr,
                          flags.character_set_client_num,
                          flags.character_set_results_num,
                          flags.collation_connection_num,
                          (ulong) flags.limit,
                          (ulong) flags.time_zone,
                          flags.sql_mode,
                          flags.max_sort_length,
                          flags.group_concat_max_len,
                          flags.div_precision_increment,
                          flags.default_week_format,
                          (int)flags.in_trans,
                          (int)flags.autocommit));

  cache_key= make_cache_key(thd, opt_query_cache_strip_comments
                            ? stripped_query : thd->query(), &flags,
                            &tot_length);
  if (cache_key == NULL)
    goto err_unlock;

  query_block = (Query_cache_block *)  my_hash_search(&queries,
                                                      (uchar*) cache_key,
                                                      tot_length);
  /* Quick abort on unlocked data */
  if (query_block == 0 ||
      query_block->query()->result() == 0 ||
      query_block->query()->result()->type != Query_cache_block::RESULT)
  {
    DBUG_PRINT("qcache", ("No query in query hash or no results"));
    goto err_unlock;
  }
  DBUG_PRINT("qcache", ("Query in query hash 0x%lx", (ulong)query_block));

  /*
    We only need to clear the diagnostics area when we actually
    find the query, as in all other cases, we'll go through
    regular parsing and execution, where the DA will be reset
    as needed, anyway.

    We're not pushing/popping a private DA here the way we do for
    parsing; if we got this far, we know we've got a SELECT on our
    hands and not a diagnotics statement that might need the
    previous statement's diagnostics area, so we just clear the DA.

    We're doing it here and not in the caller as there's three of
    them (PS, SP, interactive).  Doing it any earlier in this routine
    would reset the DA in "SELECT @@error_count"/"SELECT @@warning_count"
    before we can save the counts we'll need later (QC will see the
    SELECT go into this branch, but since we haven't parsed yet, we
    don't know yet that it's one of those legacy variables that require
    saving and basically turn SELECT into a sort of, sort of not
    diagnostics command.  Ugly stuff.
  */
  thd->get_stmt_da()->reset_diagnostics_area();
  thd->get_stmt_da()->reset_condition_info(thd);

  /* Now lock and test that nothing changed while blocks was unlocked */
  BLOCK_LOCK_RD(query_block);

  query = query_block->query();
  result_block= query->result();
#ifndef EMBEDDED_LIBRARY
  first_result_block= result_block;
#endif

  if (result_block == 0 || result_block->type != Query_cache_block::RESULT)
  {
    /* The query is probably yet processed */
    DBUG_PRINT("qcache", ("query found, but no data or data incomplete"));
    BLOCK_UNLOCK_RD(query_block);
    goto err_unlock;
  }
  DBUG_PRINT("qcache", ("Query have result 0x%lx", (ulong) query));

  if (thd->in_multi_stmt_transaction_mode() &&
      (query->tables_type() & HA_CACHE_TBL_TRANSACT))
  {
    DBUG_PRINT("qcache",
	       ("we are in transaction and have transaction tables in query"));
    BLOCK_UNLOCK_RD(query_block);
    goto err_unlock;
  }

  // Check access;
  THD_STAGE_INFO(thd, stage_checking_privileges_on_cached_query);
  block_table= query_block->table(0);
  block_table_end= block_table+query_block->n_tables;
  for (; block_table != block_table_end; block_table++)
  {
    TABLE_LIST table_list;
    TABLE *tmptable;
    Query_cache_table *table = block_table->parent;

    /*
      Check that we have not temporary tables with same names of tables
      of this query. If we have such tables, we will not send data from
      query cache, because temporary tables hide real tables by which
      query in query cache was made.
    */
    for (tmptable= thd->temporary_tables; tmptable ; tmptable= tmptable->next)
    {
      if (tmptable->s->table_cache_key.length - TMP_TABLE_KEY_EXTRA ==
          table->key_length() &&
          !memcmp(tmptable->s->table_cache_key.str, table->data(),
                  table->key_length()))
      {
        DBUG_PRINT("qcache",
                   ("Temporary table detected: '%s.%s'",
                    tmptable->s->db.str, tmptable->s->table_name.str));
        unlock();
        /*
          We should not store result of this query because it contain
          temporary tables => assign following variable to make check
          faster.
        */
        thd->lex->safe_to_cache_query=0;
        BLOCK_UNLOCK_RD(query_block);
        DBUG_RETURN(-1);
      }
    }

    table_list.db = table->db();
    table_list.alias= table_list.table_name= table->table();
#ifndef NO_EMBEDDED_ACCESS_CHECKS
    if (check_table_access(thd,SELECT_ACL,&table_list, FALSE, 1,TRUE))
    {
      DBUG_PRINT("qcache",
		 ("probably no SELECT access to %s.%s =>  return to normal processing",
		  table_list.db, table_list.alias));
      unlock();
      thd->lex->safe_to_cache_query=0;		// Don't try to cache this
      BLOCK_UNLOCK_RD(query_block);
      DBUG_RETURN(-1);				// Privilege error
    }
    assert((SELECT_ACL & ~table_list.grant.privilege) ==
           table_list.grant.want_privilege);
    if ((table_list.grant.privilege & SELECT_ACL) == 0)
    {
      DBUG_PRINT("qcache", ("Need to check column privileges for %s.%s",
			    table_list.db, table_list.alias));
      BLOCK_UNLOCK_RD(query_block);
      thd->lex->safe_to_cache_query= 0;		// Don't try to cache this
      goto err_unlock;				// Parse query
    }
#endif /*!NO_EMBEDDED_ACCESS_CHECKS*/
    engine_data= table->engine_data();
    if (table->callback())
    {
      char qcache_se_key_name[FN_REFLEN + 1];
      size_t qcache_se_key_len;
      engine_data= table->engine_data();

      qcache_se_key_len= build_table_filename(qcache_se_key_name,
                                              sizeof(qcache_se_key_name),
                                              table->db(), table->table(),
                                              "", 0);

      if (!(*table->callback())(thd, qcache_se_key_name,
                                static_cast<uint>(qcache_se_key_len),
                                &engine_data))
      {
        DBUG_PRINT("qcache", ("Handler does not allow caching for %s.%s",
                               table_list.db, table_list.alias));
        BLOCK_UNLOCK_RD(query_block);
        if (engine_data != table->engine_data())
        {
          DBUG_PRINT("qcache",
                     ("Handler require invalidation queries of %s.%s %lu-%lu",
                      table_list.db, table_list.alias,
                      (ulong) engine_data, (ulong) table->engine_data()));
          invalidate_table_internal(thd, (uchar *) table->db(),
                                    table->key_length());
        }
        else
          thd->lex->safe_to_cache_query= 0;       // Don't try to cache this
        /*
          End the statement transaction potentially started by engine.
          Currently our engines do not request rollback from callbacks.
          If this is going to change code needs to be reworked.
        */
        assert(! thd->transaction_rollback_request);
        trans_rollback_stmt(thd);
        goto err_unlock;				// Parse query
     }
   }
    else
      DBUG_PRINT("qcache", ("handler allow caching %s,%s",
			    table_list.db, table_list.alias));
  }
  move_to_query_list_end(query_block);
  hits++;
  unlock();

  /*
    Send cached result to client
  */
#ifndef EMBEDDED_LIBRARY
  THD_STAGE_INFO(thd, stage_sending_cached_result_to_client);
  do
  {
    DBUG_PRINT("qcache", ("Results  (len: %lu  used: %lu  headers: %lu)",
			  result_block->length, result_block->used,
			  (ulong) (result_block->headers_len()+
                                   ALIGN_SIZE(sizeof(Query_cache_result)))));

    Query_cache_result *result = result_block->result();
    if (send_data_in_chunks(thd->get_protocol_classic()->get_net(),
                            result->data(),
                            result_block->used -
                            result_block->headers_len() -
                            ALIGN_SIZE(sizeof(Query_cache_result))))
      break;                                    // Client aborted
    result_block = result_block->next;
    // Keep packet number updated
    thd->get_protocol_classic()->set_pkt_nr(query->last_pkt_nr);
  } while (result_block != first_result_block);
#else
  {
    Querycache_stream qs(result_block, result_block->headers_len() +
			 ALIGN_SIZE(sizeof(Query_cache_result)));
    emb_load_querycache_result(thd, &qs);
  }
#endif /*!EMBEDDED_LIBRARY*/

  thd->current_found_rows= query->found_rows();
  thd->update_previous_found_rows();
  thd->clear_current_query_costs();
  thd->save_current_query_costs();

  {
    Opt_trace_start ots(thd, NULL, SQLCOM_SELECT, NULL,
                        thd->query().str, thd->query().length, NULL,
                        thd->variables.character_set_client);

    Opt_trace_object (&thd->opt_trace)
      .add("query_result_read_from_cache", true);
  }

  /*
    End the statement transaction potentially started by an
    engine callback. We ignore the return value for now,
    since as long as EOF packet is part of the query cache
    response, we can't handle it anyway.
  */
  (void) trans_commit_stmt(thd);
  thd->query_plan_flags|= QPLAN_QC;
  if (!thd->get_stmt_da()->is_set())
    thd->get_stmt_da()->disable_status();

  BLOCK_UNLOCK_RD(query_block);
  MYSQL_QUERY_CACHE_HIT(const_cast<char*>(thd->query().str),
                        (ulong) thd->current_found_rows);
  DBUG_RETURN(1);				// Result sent to client

err_unlock:
  unlock();
err:
  thd->query_plan_flags|= QPLAN_QC_NO;
  MYSQL_QUERY_CACHE_MISS(const_cast<char*>(thd->query().str));
  DBUG_RETURN(0);				// Query was not cached
}


/**
  Remove all cached queries that use the given table.

  @param thd                 Thread handle
  @param table_used          TABLE_LIST representing the table to be
                             invalidated.
  @param using_transactions  If we are inside a transaction only add
                             the table to a list of changed tables for now,
                             don't invalidate directly. The table will instead
                             be invalidated once the transaction commits.
*/

void Query_cache::invalidate_single(THD *thd, TABLE_LIST *table_used,
                                    my_bool using_transactions)
{
  DBUG_ENTER("Query_cache::invalidate_single (table list)");
  if (is_disabled())
    DBUG_VOID_RETURN;

  using_transactions&= thd->in_multi_stmt_transaction_mode();
  assert(!using_transactions || table_used->table!=0);
  assert(!table_used->is_view_or_derived());
  if (table_used->is_view_or_derived())
    DBUG_VOID_RETURN;
  if (using_transactions &&
      (table_used->table->file->table_cache_type() ==
       HA_CACHE_TBL_TRANSACT))
    /*
      table_used->table can't be 0 in transaction.
      Only 'drop' invalidate not opened table, but 'drop'
      force transaction finish.
    */
    thd->add_changed_table(table_used->table);
  else
    invalidate_table(thd, table_used);

  DBUG_VOID_RETURN;
}

/**
  Remove all cached queries that use any of the tables in the list.

  @see Query_cache::invalidate_single().
*/

void Query_cache::invalidate(THD *thd, TABLE_LIST *tables_used,
			     my_bool using_transactions)
{
  DBUG_ENTER("Query_cache::invalidate (table list)");
  if (is_disabled())
    DBUG_VOID_RETURN;

  using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
  for (; tables_used; tables_used= tables_used->next_local)
    invalidate_single(thd, tables_used, using_transactions);

  DEBUG_SYNC(thd, "wait_after_query_cache_invalidate");

  DBUG_VOID_RETURN;
}

void Query_cache::invalidate(CHANGED_TABLE_LIST *tables_used)
{
  DBUG_ENTER("Query_cache::invalidate (changed table list)");
  if (is_disabled())
    DBUG_VOID_RETURN;

  THD *thd= current_thd;
  for (; tables_used; tables_used= tables_used->next)
  {
    THD_STAGE_INFO(thd, stage_invalidating_query_cache_entries_table_list);
    invalidate_table(thd, (uchar*) tables_used->key, tables_used->key_length);
    DBUG_PRINT("qcache", ("db: %s  table: %s", tables_used->key,
                          tables_used->key+
                          strlen(tables_used->key)+1));
  }
  DBUG_VOID_RETURN;
}


/*
  Invalidate locked for write

  SYNOPSIS
    Query_cache::invalidate_locked_for_write()
    tables_used - table list

  NOTE
    can be used only for opened tables
*/
void Query_cache::invalidate_locked_for_write(TABLE_LIST *tables_used)
{
  DBUG_ENTER("Query_cache::invalidate_locked_for_write");
  if (is_disabled())
    DBUG_VOID_RETURN;

  THD *thd= current_thd;
  for (; tables_used; tables_used= tables_used->next_local)
  {
    THD_STAGE_INFO(thd, stage_invalidating_query_cache_entries_table);
    if (tables_used->lock_type >= TL_WRITE_ALLOW_WRITE &&
        tables_used->table)
    {
      invalidate_table(thd, tables_used->table);
    }
  }
  DBUG_VOID_RETURN;
}

/*
  Remove all cached queries that uses the given table
*/

void Query_cache::invalidate(THD *thd, TABLE *table,
			     my_bool using_transactions)
{
  DBUG_ENTER("Query_cache::invalidate (table)");
  if (is_disabled())
    DBUG_VOID_RETURN;

  using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
  if (using_transactions &&
      (table->file->table_cache_type() == HA_CACHE_TBL_TRANSACT))
    thd->add_changed_table(table);
  else
    invalidate_table(thd, table);


  DBUG_VOID_RETURN;
}

void Query_cache::invalidate(THD *thd, const char *key, uint32  key_length,
			     my_bool using_transactions)
{
  DBUG_ENTER("Query_cache::invalidate (key)");
  if (is_disabled())
   DBUG_VOID_RETURN;

  using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
  if (using_transactions) // used for innodb => has_transactions() is TRUE
    thd->add_changed_table(key, key_length);
  else
    invalidate_table(thd, (uchar*)key, key_length);

  DBUG_VOID_RETURN;
}


/**
   Remove all cached queries that uses the given database.
*/

void Query_cache::invalidate(const char *db)
{

  DBUG_ENTER("Query_cache::invalidate (db)");
  if (is_disabled())
    DBUG_VOID_RETURN;

  bool restart= FALSE;
  /*
    Lock the query cache and queue all invalidation attempts to avoid
    the risk of a race between invalidation, cache inserts and flushes.
  */
  lock();

  THD *thd= current_thd;

  if (query_cache_size > 0)
  {
    if (tables_blocks)
    {
      Query_cache_block *table_block = tables_blocks;
      do {
        restart= FALSE;
        do
        {
          Query_cache_block *next= table_block->next;
          Query_cache_table *table = table_block->table();
          if (strcmp(table->db(),db) == 0)
          {
            Query_cache_block_table *list_root= table_block->table(0);
            invalidate_query_block_list(thd,list_root);
          }

          table_block= next;

          /*
            If our root node to used tables became null then the last element
            in the table list was removed when a query was invalidated;
            Terminate the search.
          */
          if (tables_blocks == 0)
          {
            table_block= tables_blocks;
          }
          /*
            If the iterated list has changed underlying structure;
            we need to restart the search.
          */
          else if (table_block->type == Query_cache_block::FREE)
          {
            restart= TRUE;
            table_block= tables_blocks;
          }
          /*
            The used tables are linked in a circular list;
            loop until we return to the begining.
          */
        } while (table_block != tables_blocks);
        /*
           Invalidating a table will also mean that all cached queries using
           this table also will be invalidated. This will in turn change the
           list of tables associated with these queries and the linked list of
           used table will be changed. Because of this we might need to restart
           the search when a table has been invalidated.
        */
      } while (restart);
    } // end if( tables_blocks )
  }
  unlock();

  DBUG_VOID_RETURN;
}


void Query_cache::invalidate_by_MyISAM_filename(const char *filename)
{
  DBUG_ENTER("Query_cache::invalidate_by_MyISAM_filename");

  /* Calculate the key outside the lock to make the lock shorter */
  char key[MAX_DBKEY_LENGTH];
  size_t db_length;
  size_t key_length= filename_2_table_key(key, filename, &db_length);
  THD *thd= current_thd;
  invalidate_table(thd,(uchar *)key, key_length);
  DBUG_EXECUTE("check_querycache", check_integrity(LOCK_WHILE_CHECKING););
  DBUG_VOID_RETURN;
}

  /* Remove all queries from cache */

void Query_cache::flush()
{
  DBUG_ENTER("Query_cache::flush");
  if (is_disabled())
    DBUG_VOID_RETURN;

  QC_DEBUG_SYNC("wait_in_query_cache_flush1");

  lock_and_suspend();
  if (query_cache_size > 0)
  {
    DUMP(this);
    flush_cache();
    DUMP(this);
  }

  DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););
  unlock();
  DBUG_VOID_RETURN;
}


/**
  Rearrange the memory blocks and join result in cache in 1 block (if
  result length > join_limit)

  @param[in] join_limit If the minimum length of a result block to be joined.
  @param[in] iteration_limit The maximum number of packing and joining
    sequences.

*/

void Query_cache::pack(ulong join_limit, uint iteration_limit)
{
  DBUG_ENTER("Query_cache::pack");

  if (is_disabled())
    DBUG_VOID_RETURN;

  /*
    If the entire qc is being invalidated we can bail out early
    instead of waiting for the lock.
  */
  if (try_lock())
    DBUG_VOID_RETURN;

  if (query_cache_size == 0)
  {
    unlock();
    DBUG_VOID_RETURN;
  }

  uint i = 0;
  do
  {
    pack_cache();
  } while ((++i < iteration_limit) && join_results(join_limit));

  unlock();
  DBUG_VOID_RETURN;
}


void Query_cache::destroy()
{
  DBUG_ENTER("Query_cache::destroy");
  if (!initialized)
  {
    DBUG_PRINT("qcache", ("Query Cache not initialized"));
  }
  else
  {
    /* Underlying code expects the lock. */
    lock_and_suspend();
    free_cache();
    unlock();

    mysql_cond_destroy(&COND_cache_status_changed);
    mysql_mutex_destroy(&structure_guard_mutex);
    initialized = 0;
  }
  DBUG_VOID_RETURN;
}


/*****************************************************************************
  init/destroy
*****************************************************************************/

void Query_cache::init()
{
  DBUG_ENTER("Query_cache::init");
  mysql_mutex_init(key_structure_guard_mutex,
                   &structure_guard_mutex, MY_MUTEX_INIT_FAST);
  mysql_cond_init(key_COND_cache_status_changed,
                  &COND_cache_status_changed);
  m_cache_lock_status= Query_cache::UNLOCKED;
  initialized = 1;
  /*
    If we explicitly turn off query cache from the command line query cache will
    be disabled for the reminder of the server life time. This is because we
    want to avoid locking the QC specific mutex if query cache isn't going to
    be used.
  */
  if (global_system_variables.query_cache_type == 0)
    query_cache.disable_query_cache();

  DBUG_VOID_RETURN;
}


ulong Query_cache::init_cache()
{
  uint mem_bin_count, num, step;
  ulong mem_bin_size, prev_size, inc;
  ulong additional_data_size, max_mem_bin_size, approx_additional_data_size;
  int align;

  DBUG_ENTER("Query_cache::init_cache");

  approx_additional_data_size = (/* FIXME: WHAT FOR ? sizeof(Query_cache) + */
				 sizeof(uchar*)*(def_query_hash_size+
					       def_table_hash_size));
  if (query_cache_size < approx_additional_data_size)
    goto err;

  query_cache_size-= approx_additional_data_size;
  align= query_cache_size % ALIGN_SIZE(1);
  if (align)
  {
    query_cache_size-= align;
    approx_additional_data_size+= align;
  }

  /*
    Count memory bins number.
    Check section 6. in start comment for the used algorithm.
  */

  max_mem_bin_size = query_cache_size >> QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2;
  mem_bin_count = (uint)  ((1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
			   QUERY_CACHE_MEM_BIN_PARTS_MUL);
  mem_bin_num = 1;
  mem_bin_steps = 1;
  mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
  prev_size = 0;
  if (mem_bin_size <= min_allocation_unit)
  {
    DBUG_PRINT("qcache", ("too small query cache => query cache disabled"));
    // TODO here (and above) should be warning in 4.1
    goto err;
  }
  while (mem_bin_size > min_allocation_unit)
  {
    mem_bin_num += mem_bin_count;
    prev_size = mem_bin_size;
    mem_bin_size >>= QUERY_CACHE_MEM_BIN_STEP_PWR2;
    mem_bin_steps++;
    mem_bin_count += QUERY_CACHE_MEM_BIN_PARTS_INC;
    mem_bin_count = (uint) (mem_bin_count * QUERY_CACHE_MEM_BIN_PARTS_MUL);

    // Prevent too small bins spacing
    if (mem_bin_count > (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2))
      mem_bin_count= (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2);
  }
  inc = (prev_size - mem_bin_size) / mem_bin_count;
  mem_bin_num += (mem_bin_count - (min_allocation_unit - mem_bin_size)/inc);
  mem_bin_steps++;
  additional_data_size = ((mem_bin_num+1) *
			  ALIGN_SIZE(sizeof(Query_cache_memory_bin))+
			  (mem_bin_steps *
			   ALIGN_SIZE(sizeof(Query_cache_memory_bin_step))));

  if (query_cache_size < additional_data_size)
    goto err;
  query_cache_size -= additional_data_size;

  if (!(cache= (uchar *)
        my_malloc(key_memory_Query_cache,
                  query_cache_size+additional_data_size, MYF(0))))
    goto err;

  DBUG_PRINT("qcache", ("cache length %lu, min unit %lu, %u bins",
		      query_cache_size, min_allocation_unit, mem_bin_num));

  steps = (Query_cache_memory_bin_step *) cache;
  bins = ((Query_cache_memory_bin *)
	  (cache + mem_bin_steps *
	   ALIGN_SIZE(sizeof(Query_cache_memory_bin_step))));

  first_block = (Query_cache_block *) (cache + additional_data_size);
  first_block->init(query_cache_size);
  total_blocks++;
  first_block->pnext=first_block->pprev=first_block;
  first_block->next=first_block->prev=first_block;

  /* Prepare bins */

  bins[0].init(max_mem_bin_size);
  steps[0].init(max_mem_bin_size,0,0);
  mem_bin_count = (uint) ((1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
			  QUERY_CACHE_MEM_BIN_PARTS_MUL);
  num= step= 1;
  mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
  while (mem_bin_size > min_allocation_unit)
  {
    ulong incr = (steps[step-1].size - mem_bin_size) / mem_bin_count;
    unsigned long size = mem_bin_size;
    for (uint i= mem_bin_count; i > 0; i--)
    {
      bins[num+i-1].init(size);
      size += incr;
    }
    num += mem_bin_count;
    steps[step].init(mem_bin_size, num-1, incr);
    mem_bin_size >>= QUERY_CACHE_MEM_BIN_STEP_PWR2;
    step++;
    mem_bin_count += QUERY_CACHE_MEM_BIN_PARTS_INC;
    mem_bin_count = (uint) (mem_bin_count * QUERY_CACHE_MEM_BIN_PARTS_MUL);
    if (mem_bin_count > (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2))
      mem_bin_count=(mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2);
  }
  inc = (steps[step-1].size - mem_bin_size) / mem_bin_count;

  /*
    num + mem_bin_count > mem_bin_num, but index never be > mem_bin_num
    because block with size < min_allocated_unit never will be requested
  */

  steps[step].init(mem_bin_size, num + mem_bin_count - 1, inc);
  {
    uint skiped = (min_allocation_unit - mem_bin_size)/inc;
    ulong size = mem_bin_size + inc*skiped;
    uint i = mem_bin_count - skiped;
    while (i-- > 0)
    {
      bins[num+i].init(size);
      size += inc;
    }
  }
  bins[mem_bin_num].number = 1;	// For easy end test in get_free_block
  free_memory = free_memory_blocks = 0;
  insert_into_free_memory_list(first_block);

  DUMP(this);

  (void) my_hash_init(&queries, &my_charset_bin, def_query_hash_size, 0, 0,
                      query_cache_query_get_key, 0, 0,
                      key_memory_Query_cache);
#ifndef FN_NO_CASE_SENSE
  /*
    If lower_case_table_names!=0 then db and table names are already
    converted to lower case and we can use binary collation for their
    comparison (no matter if file system case sensitive or not).
    If we have case-sensitive file system (like on most Unixes) and
    lower_case_table_names == 0 then we should distinguish my_table
    and MY_TABLE cases and so again can use binary collation.
  */
  (void) my_hash_init(&tables, &my_charset_bin, def_table_hash_size, 0, 0,
                      query_cache_table_get_key, 0, 0,
                      key_memory_Query_cache);
#else
  /*
    On windows, OS/2, MacOS X with HFS+ or any other case insensitive
    file system if lower_case_table_names!=0 we have same situation as
    in previous case, but if lower_case_table_names==0 then we should
    not distinguish cases (to be compatible in behavior with underlying
    file system) and so should use case insensitive collation for
    comparison.
  */
  (void) my_hash_init(&tables,
                      lower_case_table_names ? &my_charset_bin :
                      files_charset_info,
                      def_table_hash_size, 0, 0,query_cache_table_get_key,
                      0, 0,
                      key_memory_Query_cache);
#endif

  queries_in_cache = 0;
  queries_blocks = 0;
  DBUG_RETURN(query_cache_size +
	      additional_data_size + approx_additional_data_size);

err:
  make_disabled();
  DBUG_RETURN(0);
}


/* Disable the use of the query cache */

void Query_cache::make_disabled()
{
  DBUG_ENTER("Query_cache::make_disabled");
  query_cache_size= 0;
  queries_blocks= 0;
  free_memory= 0;
  free_memory_blocks= 0;
  bins= 0;
  steps= 0;
  cache= 0;
  mem_bin_num= mem_bin_steps= 0;
  queries_in_cache= 0;
  first_block= 0;
  total_blocks= 0;
  tables_blocks= 0;
  DBUG_VOID_RETURN;
}


/**
  @class Query_cache
  Free all resources allocated by the cache.

  This function frees all resources allocated by the cache.  You
  have to call init_cache() before using the cache again. This function
  requires the structure_guard_mutex to be locked.
*/

void Query_cache::free_cache()
{
  DBUG_ENTER("Query_cache::free_cache");

  my_free(cache);
  make_disabled();
  my_hash_free(&queries);
  my_hash_free(&tables);
  DBUG_VOID_RETURN;
}

/*****************************************************************************
  Free block data
*****************************************************************************/


/**
  Flush the cache.

  This function will flush cache contents.  It assumes we have
  'structure_guard_mutex' locked. The function sets the m_cache_status flag and
  releases the lock, so other threads may proceed skipping the cache as if it
  is disabled. Concurrent flushes are performed in turn.
  After flush_cache() call, the cache is flushed, all the freed memory is
  accumulated in bin[0], and the 'structure_guard_mutex' is locked. However,
  since we could release the mutex during execution, the rest of the cache
  state could have been changed, and should not be relied on.
*/

void Query_cache::flush_cache()
{
  QC_DEBUG_SYNC("wait_in_query_cache_flush2");

  my_hash_reset(&queries);
  while (queries_blocks != 0)
  {
    BLOCK_LOCK_WR(queries_blocks);
    free_query_internal(queries_blocks);
  }
}

/*
  Free oldest query that is not in use by another thread.
  Returns 1 if we couldn't remove anything
*/

my_bool Query_cache::free_old_query()
{
  DBUG_ENTER("Query_cache::free_old_query");
  if (queries_blocks)
  {
    /*
      try_lock_writing used to prevent client because here lock
      sequence is breached.
      Also we don't need remove locked queries at this point.
    */
    Query_cache_block *query_block= 0;
    if (queries_blocks != 0)
    {
      Query_cache_block *block = queries_blocks;
      /* Search until we find first query that we can remove */
      do
      {
	Query_cache_query *header = block->query();
	if (header->result() != 0 &&
	    header->result()->type == Query_cache_block::RESULT &&
	    block->query()->try_lock_writing())
	{
	  query_block = block;
	  break;
	}
      } while ((block=block->next) != queries_blocks );
    }

    if (query_block != 0)
    {
      free_query(query_block);
      lowmem_prunes++;
      DBUG_RETURN(0);
    }
  }
  DBUG_RETURN(1);				// Nothing to remove
}


/*
  free_query_internal() - free query from query cache.

  SYNOPSIS
    free_query_internal()
      query_block           Query_cache_block representing the query

  DESCRIPTION
    This function will remove the query from a cache, and place its
    memory blocks to the list of free blocks.  'query_block' must be
    locked for writing, this function will release (and destroy) this
    lock.

  NOTE
    'query_block' should be removed from 'queries' hash _before_
    calling this method, as the lock will be destroyed here.
*/

void Query_cache::free_query_internal(Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::free_query_internal");
  DBUG_PRINT("qcache", ("free query 0x%lx %lu bytes result",
		      (ulong) query_block,
		      query_block->query()->length() ));

  queries_in_cache--;

  Query_cache_query *query= query_block->query();

  if (query->writer() != 0)
  {
    /* Tell MySQL that this query should not be cached anymore */
    query->writer()->first_query_block= NULL;
    query->writer(0);
  }
  double_linked_list_exclude(query_block, &queries_blocks);
  Query_cache_block_table *table= query_block->table(0);

  for (TABLE_COUNTER_TYPE i= 0; i < query_block->n_tables; i++)
    unlink_table(table++);
  Query_cache_block *result_block= query->result();

  /*
    The following is true when query destruction was called and no results
    in query . (query just registered and then abort/pack/flush called)
  */
  if (result_block != 0)
  {
    if (result_block->type != Query_cache_block::RESULT)
    {
      // removing unfinished query
      refused++;
      inserts--;
    }
    Query_cache_block *block= result_block;
    do
    {
      Query_cache_block *current= block;
      block= block->next;
      free_memory_block(current);
    } while (block != result_block);
  }
  else
  {
    // removing unfinished query
    refused++;
    inserts--;
  }

  query->unlock_n_destroy();
  free_memory_block(query_block);

  DBUG_VOID_RETURN;
}


/*
  free_query() - free query from query cache.

  SYNOPSIS
    free_query()
      query_block           Query_cache_block representing the query

  DESCRIPTION
    This function will remove 'query_block' from 'queries' hash, and
    then call free_query_internal(), which see.
*/

void Query_cache::free_query(Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::free_query");
  DBUG_PRINT("qcache", ("free query 0x%lx %lu bytes result",
		      (ulong) query_block,
		      query_block->query()->length() ));

  my_hash_delete(&queries,(uchar *) query_block);
  free_query_internal(query_block);

  DBUG_VOID_RETURN;
}

/*****************************************************************************
 Query data creation
*****************************************************************************/

Query_cache_block *
Query_cache::write_block_data(size_t data_len, uchar* data,
                              size_t header_len,
                              Query_cache_block::block_type type,
                              TABLE_COUNTER_TYPE ntab)
{
  size_t all_headers_len= (ALIGN_SIZE(sizeof(Query_cache_block)) +
                          ALIGN_SIZE(ntab*sizeof(Query_cache_block_table)) +
                          header_len);
  size_t len = data_len + all_headers_len;
  size_t align_len= ALIGN_SIZE(len);
  DBUG_ENTER("Query_cache::write_block_data");
  DBUG_PRINT("qcache", ("data: %zu, header: %zu, all header: %zu",
		                   data_len, header_len, all_headers_len));
  Query_cache_block *block= allocate_block(max<size_t>(align_len,
                                           min_allocation_unit),1, 0);
  if (block != 0)
  {
    block->type = type;
    block->n_tables = ntab;
    block->used = static_cast<ulong>(len);

    memcpy((uchar *) block+ all_headers_len, data, data_len);
  }
  DBUG_RETURN(block);
}


my_bool
Query_cache::append_result_data(Query_cache_block **current_block,
				ulong data_len, uchar* data,
				Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::append_result_data");
  DBUG_PRINT("qcache", ("append %lu bytes to 0x%lx query",
		      data_len, (long) query_block));

  if (query_block->query()->add(data_len) > query_cache_limit)
  {
    DBUG_PRINT("qcache", ("size limit reached %lu > %lu",
			query_block->query()->length(),
			query_cache_limit));
    DBUG_RETURN(0);
  }
  if (*current_block == 0)
  {
    DBUG_PRINT("qcache", ("allocated first result data block %lu", data_len));
    DBUG_RETURN(write_result_data(current_block, data_len, data, query_block,
				  Query_cache_block::RES_BEG));
  }
  Query_cache_block *last_block = (*current_block)->prev;

  DBUG_PRINT("qcache", ("lastblock 0x%lx len %lu used %lu",
		      (ulong) last_block, last_block->length,
		      last_block->used));
  my_bool success = 1;
  ulong last_block_free_space= last_block->length - last_block->used;

  /*
    We will first allocate and write the 'tail' of data, that doesn't fit
    in the 'last_block'.  Only if this succeeds, we will fill the last_block.
    This saves us a memcpy if the query doesn't fit in the query cache.
  */

  // Try join blocks if physically next block is free...
  ulong tail = data_len - last_block_free_space;
  ulong append_min = get_min_append_result_data_size();
  if (last_block_free_space < data_len &&
      append_next_free_block(last_block,
			     max(tail, append_min)))
    last_block_free_space = last_block->length - last_block->used;
  // If no space in last block (even after join) allocate new block
  if (last_block_free_space < data_len)
  {
    DBUG_PRINT("qcache", ("allocate new block for %lu bytes",
			data_len-last_block_free_space));
    Query_cache_block *new_block = 0;
    success = write_result_data(&new_block, data_len-last_block_free_space,
				(uchar*)(data+last_block_free_space),
				query_block,
				Query_cache_block::RES_CONT);
    /*
       new_block may be != 0 even !success (if write_result_data
       allocate a small block but failed to allocate continue)
    */
    if (new_block != 0)
      double_linked_list_join(last_block, new_block);
  }
  else
  {
    // It is success (nobody can prevent us write data)
    unlock();
  }

  // Now finally write data to the last block
  if (success && last_block_free_space > 0)
  {
    ulong to_copy = min(data_len,last_block_free_space);
    DBUG_PRINT("qcache", ("use free space %lub at block 0x%lx to copy %lub",
			last_block_free_space, (ulong)last_block, to_copy));
    memcpy((uchar*) last_block + last_block->used, data, to_copy);
    last_block->used+=to_copy;
  }
  DBUG_RETURN(success);
}


my_bool Query_cache::write_result_data(Query_cache_block **result_block,
				       ulong data_len, uchar* data,
				       Query_cache_block *query_block,
				       Query_cache_block::block_type type)
{
  DBUG_ENTER("Query_cache::write_result_data");
  DBUG_PRINT("qcache", ("data_len %lu",data_len));

  /*
    Reserve block(s) for filling
    During data allocation we must have structure_guard_mutex locked.
    As data copy is not a fast operation, it's better if we don't have
    structure_guard_mutex locked during data coping.
    Thus we first allocate space and lock query, then unlock
    structure_guard_mutex and copy data.
  */

  my_bool success = allocate_data_chain(result_block, data_len, query_block,
					type == Query_cache_block::RES_BEG);
  if (success)
  {
    // It is success (nobody can prevent us write data)
    unlock();
    uint headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
			ALIGN_SIZE(sizeof(Query_cache_result)));
#ifndef EMBEDDED_LIBRARY
    Query_cache_block *block= *result_block;
    uchar *rest= data;
    // Now fill list of blocks that created by allocate_data_chain
    do
    {
      block->type = type;
      ulong length = block->used - headers_len;
      DBUG_PRINT("qcache", ("write %lu byte in block 0x%lx",length,
			    (ulong)block));
      memcpy((uchar*) block+headers_len, rest, length);
      rest += length;
      block = block->next;
      type = Query_cache_block::RES_CONT;
    } while (block != *result_block);
#else
    /*
      Set type of first block, emb_store_querycache_result() will handle
      the others.
    */
    (*result_block)->type= type;
    Querycache_stream qs(*result_block, headers_len);
    emb_store_querycache_result(&qs, (THD*)data);
#endif /*!EMBEDDED_LIBRARY*/
  }
  else
  {
    if (*result_block != 0)
    {
      // Destroy list of blocks that was created & locked by lock_result_data
      Query_cache_block *block = *result_block;
      do
      {
	Query_cache_block *current = block;
	block = block->next;
	free_memory_block(current);
      } while (block != *result_block);
      *result_block = 0;
      /*
	It is not success => not unlock structure_guard_mutex (we need it to
	free query)
      */
    }
  }
  DBUG_PRINT("qcache", ("success %d", (int) success));
  DBUG_RETURN(success);
}

inline ulong Query_cache::get_min_first_result_data_size()
{
  if (queries_in_cache < QUERY_CACHE_MIN_ESTIMATED_QUERIES_NUMBER)
    return min_result_data_size;
  ulong avg_result = (query_cache_size - free_memory) / queries_in_cache;
  avg_result = min(avg_result, query_cache_limit);
  return max(min_result_data_size, avg_result);
}

inline ulong Query_cache::get_min_append_result_data_size()
{
  return min_result_data_size;
}

/*
  Allocate one or more blocks to hold data
*/
my_bool Query_cache::allocate_data_chain(Query_cache_block **result_block,
					 ulong data_len,
					 Query_cache_block *query_block,
					 my_bool first_block_arg)
{
  ulong all_headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
			   ALIGN_SIZE(sizeof(Query_cache_result)));
  ulong min_size = (first_block_arg ?
		    get_min_first_result_data_size():
		    get_min_append_result_data_size());
  Query_cache_block *prev_block= NULL;
  Query_cache_block *new_block;
  DBUG_ENTER("Query_cache::allocate_data_chain");
  DBUG_PRINT("qcache", ("data_len %lu, all_headers_len %lu",
			data_len, all_headers_len));

  do
  {
    ulong len= data_len + all_headers_len;
    ulong align_len= ALIGN_SIZE(len);

    if (!(new_block= allocate_block(max(min_size, align_len),
				    min_result_data_size == 0,
				    all_headers_len + min_result_data_size)))
    {
      DBUG_PRINT("warning", ("Can't allocate block for results"));
      DBUG_RETURN(FALSE);
    }

    new_block->n_tables = 0;
    new_block->used = min(len, new_block->length);
    new_block->type = Query_cache_block::RES_INCOMPLETE;
    new_block->next = new_block->prev = new_block;
    Query_cache_result *header = new_block->result();
    header->parent(query_block);

    DBUG_PRINT("qcache", ("Block len %lu used %lu",
			  new_block->length, new_block->used));

    if (prev_block)
      double_linked_list_join(prev_block, new_block);
    else
      *result_block= new_block;
    if (new_block->length >= len)
      break;

    /*
      We got less memory then we need (no big memory blocks) =>
      Continue to allocated more blocks until we got everything we need.
    */
    data_len= len - new_block->length;
    prev_block= new_block;
  } while (1);

  DBUG_RETURN(TRUE);
}

/*****************************************************************************
  Tables management
*****************************************************************************/

/*
  Invalidate the first table in the table_list
*/

void Query_cache::invalidate_table(THD *thd, TABLE_LIST *table_list)
{
  if (table_list->table != 0)
    invalidate_table(thd, table_list->table);	// Table is open
  else
  {
    const char *key;
    size_t key_length;
    key_length= get_table_def_key(table_list, &key);

    // We don't store temporary tables => no key_length+=4 ...
    invalidate_table(thd, (uchar *)key, key_length);
  }
}

void Query_cache::invalidate_table(THD *thd, TABLE *table)
{
  invalidate_table(thd, (uchar*) table->s->table_cache_key.str,
                   table->s->table_cache_key.length);
}

void Query_cache::invalidate_table(THD *thd, uchar * key, size_t key_length)
{
  DEBUG_SYNC(thd, "wait_in_query_cache_invalidate1");

  /*
    Lock the query cache and queue all invalidation attempts to avoid
    the risk of a race between invalidation, cache inserts and flushes.
  */
  lock();

  DEBUG_SYNC(thd, "wait_in_query_cache_invalidate2");

  if (query_cache_size > 0)
    invalidate_table_internal(thd, key, key_length);

  unlock();
}


/**
  Try to locate and invalidate a table by name.
  The caller must ensure that no other thread is trying to work with
  the query cache when this function is executed.

  @pre structure_guard_mutex is acquired or LOCKED is set.
*/

void
Query_cache::invalidate_table_internal(THD *thd, uchar *key, size_t key_length)
{
  Query_cache_block *table_block=
    (Query_cache_block*)my_hash_search(&tables, key, key_length);
  if (table_block)
  {
    Query_cache_block_table *list_root= table_block->table(0);
    invalidate_query_block_list(thd, list_root);
  }
}

/**
  Invalidate a linked list of query cache blocks.

  Each block tries to acquire a block level lock before
  free_query is a called. This function will in turn affect
  related table- and result-blocks.

  @param[in,out] thd Thread context.
  @param[in,out] list_root A pointer to a circular list of query blocks.

*/

void
Query_cache::invalidate_query_block_list(THD *thd,
                                         Query_cache_block_table *list_root)
{
  while (list_root->next != list_root)
  {
    Query_cache_block *query_block= list_root->next->block();
    BLOCK_LOCK_WR(query_block);
    free_query(query_block);
  }
}

/*
  Register given table list begining with given position in tables table of
  block

  SYNOPSIS
    Query_cache::register_tables_from_list
    tables_used     given table list
    counter         number current position in table of tables of block
    block_table     pointer to current position in tables table of block

  RETURN
    0   error
    number of next position of table entry in table of tables of block
*/

TABLE_COUNTER_TYPE
Query_cache::register_tables_from_list(TABLE_LIST *tables_used,
                                       TABLE_COUNTER_TYPE counter,
                                       Query_cache_block_table *block_table)
{
  TABLE_COUNTER_TYPE n;
  DBUG_ENTER("Query_cache::register_tables_from_list");
  for (n= counter;
       tables_used;
       tables_used= tables_used->next_global, n++, block_table++)
  {
    if (tables_used->is_derived())
    {
      DBUG_PRINT("qcache", ("derived table skipped"));
      n--;
      block_table--;
      continue;
    }
    block_table->n= n;
    if (tables_used->is_view())
    {
      const char *key;
      size_t key_length;
      DBUG_PRINT("qcache", ("view: %s  db: %s",
                            tables_used->view_name.str,
                            tables_used->view_db.str));
      key_length= get_table_def_key(tables_used, &key);
      /*
        There are not callback function for for VIEWs
      */
      if (!insert_table(key_length, key, block_table,
                        tables_used->view_db.length + 1,
                        HA_CACHE_TBL_NONTRANSACT, 0, 0))
        DBUG_RETURN(0);
      /*
        We do not need to register view tables here because they are already
        present in the global list.
      */
    }
    else
    {
      DBUG_PRINT("qcache",
                 ("table: %s  db: %s  openinfo:  0x%lx  keylen: %lu  key: 0x%lx",
                  tables_used->table->s->table_name.str,
                  tables_used->table->s->table_cache_key.str,
                  (ulong) tables_used->table,
                  (ulong) tables_used->table->s->table_cache_key.length,
                  (ulong) tables_used->table->s->table_cache_key.str));

      if (!insert_table(tables_used->table->s->table_cache_key.length,
                        tables_used->table->s->table_cache_key.str,
                        block_table,
                        tables_used->db_length,
                        tables_used->table->file->table_cache_type(),
                        tables_used->callback_func,
                        tables_used->engine_data))
        DBUG_RETURN(0);

      /*
        XXX FIXME: Some generic mechanism is required here instead of this
        MYISAMMRG-specific implementation.
      */
      if (tables_used->table->s->db_type()->db_type == DB_TYPE_MRG_MYISAM)
      {
        ha_myisammrg *handler = (ha_myisammrg *) tables_used->table->file;
        MYRG_INFO *file = handler->myrg_info();
        for (MYRG_TABLE *table = file->open_tables;
             table != file->end_table ;
             table++)
        {
          char key[MAX_DBKEY_LENGTH];
          size_t db_length;
          size_t key_length= filename_2_table_key(key, table->table->filename,
                                                  &db_length);
          (++block_table)->n= ++n;
          /*
            There are not callback function for for MyISAM, and engine data
          */
          if (!insert_table(key_length, key, block_table,
                            db_length,
                            tables_used->table->file->table_cache_type(),
                            0, 0))
            DBUG_RETURN(0);
        }
      }
    }
  }
  DBUG_RETURN(n - counter);
}

/*
  Store all used tables

  SYNOPSIS
    register_all_tables()
    block		Store tables in this block
    tables_used		List if used tables
    tables_arg		Not used ?
*/

my_bool Query_cache::register_all_tables(Query_cache_block *block,
					 TABLE_LIST *tables_used,
					 TABLE_COUNTER_TYPE tables_arg)
{
  TABLE_COUNTER_TYPE n;
  DBUG_PRINT("qcache", ("register tables block 0x%lx, n %d, header %x",
		      (ulong) block, (int) tables_arg,
		      (int) ALIGN_SIZE(sizeof(Query_cache_block))));

  Query_cache_block_table *block_table = block->table(0);

  n= register_tables_from_list(tables_used, 0, block_table);

  if (n==0)
  {
    /* Unlink the tables we allocated above */
    for (Query_cache_block_table *tmp = block->table(0) ;
	 tmp != block_table;
	 tmp++)
      unlink_table(tmp);
  }
  return MY_TEST(n);
}


/**
  Insert used table name into the cache.

  @return Error status
    @retval FALSE On error
    @retval TRUE On success
*/

my_bool
Query_cache::insert_table(size_t key_len, const char *key,
                          Query_cache_block_table *node,
                          size_t db_length, uint8 cache_type,
                          qc_engine_callback callback,
                          ulonglong engine_data)
{
  DBUG_ENTER("Query_cache::insert_table");
  DBUG_PRINT("qcache", ("insert table node 0x%lx, len %zu",
                        (ulong)node, key_len));

  THD *thd= current_thd;

  Query_cache_block *table_block=
    (Query_cache_block *) my_hash_search(&tables, (uchar*) key, key_len);

  if (table_block &&
      table_block->table()->engine_data() != engine_data)
  {
    DBUG_PRINT("qcache",
               ("Handler require invalidation queries of %s.%s %lu-%lu",
                table_block->table()->db(),
                table_block->table()->table(),
                (ulong) engine_data,
                (ulong) table_block->table()->engine_data()));
    /*
      as far as we delete all queries with this table, table block will be
      deleted, too
    */
    {
      Query_cache_block_table *list_root= table_block->table(0);
      invalidate_query_block_list(thd, list_root);
    }

    table_block= 0;
  }

  if (table_block == 0)
  {
    DBUG_PRINT("qcache", ("new table block from 0x%lx (%u)",
			(ulong) key, (int) key_len));
    table_block= write_block_data(key_len, (uchar*) key,
                                  ALIGN_SIZE(sizeof(Query_cache_table)),
                                  Query_cache_block::TABLE, 1);
    if (table_block == 0)
    {
      DBUG_PRINT("qcache", ("Can't write table name to cache"));
      DBUG_RETURN(0);
    }
    Query_cache_table *header= table_block->table();
    double_linked_list_simple_include(table_block,
                                      &tables_blocks);
    /*
      First node in the Query_cache_block_table-chain is the table-type
      block. This block will only have one Query_cache_block_table (n=0).
    */
    Query_cache_block_table *list_root= table_block->table(0);
    list_root->n= 0;

    /*
      The node list is circular in nature.
    */
    list_root->next= list_root->prev= list_root;

    if (my_hash_insert(&tables, (const uchar *) table_block))
    {
      DBUG_PRINT("qcache", ("Can't insert table to hash"));
      // write_block_data return locked block
      free_memory_block(table_block);
      DBUG_RETURN(0);
    }
    char *db= header->db();
    header->table(db + db_length + 1);
    header->key_length(key_len);
    header->type(cache_type);
    header->callback(callback);
    header->engine_data(engine_data);

    /*
      We insert this table without the assumption that it isn't refrenenced by
      any queries.
    */
    header->m_cached_query_count= 0;
  }

  /*
    Table is now in the cache; link the table_block-node associated
    with the currently processed query into the chain of queries depending
    on the cached table.
  */
  Query_cache_block_table *list_root= table_block->table(0);
  node->next= list_root->next;
  list_root->next= node;
  node->next->prev= node;
  node->prev= list_root;
  node->parent= table_block->table();
  /*
    Increase the counter to keep track on how long this chain
    of queries is.
  */
  Query_cache_table *table_block_data= table_block->table();
  table_block_data->m_cached_query_count++;
  DBUG_RETURN(1);
}


void Query_cache::unlink_table(Query_cache_block_table *node)
{
  DBUG_ENTER("Query_cache::unlink_table");
  node->prev->next= node->next;
  node->next->prev= node->prev;
  Query_cache_block_table *neighbour= node->next;
  Query_cache_table *table_block_data= node->parent;
  table_block_data->m_cached_query_count--;

  assert(table_block_data->m_cached_query_count >= 0);

  if (neighbour->next == neighbour)
  {
    assert(table_block_data->m_cached_query_count == 0);
    /*
      If neighbor is root of list, the list is empty.
      The root of the list is always a table-type block
      which contain exactly one Query_cache_block_table
      node object, thus we can use the block() method
      to calculate the Query_cache_block address.
    */
    Query_cache_block *table_block= neighbour->block();
    double_linked_list_exclude(table_block,
                               &tables_blocks);
    my_hash_delete(&tables,(uchar *) table_block);
    free_memory_block(table_block);
  }
  DBUG_VOID_RETURN;
}

/*****************************************************************************
  Free memory management
*****************************************************************************/

Query_cache_block *
Query_cache::allocate_block(size_t len, my_bool not_less, size_t minimum)
{
  DBUG_ENTER("Query_cache::allocate_block");
  DBUG_PRINT("qcache", ("len %zu, not less %d, min %zu",
             len, not_less, minimum));

  if (len >= min(query_cache_size, query_cache_limit))
  {
    DBUG_PRINT("qcache", ("Query cache hase only %lu memory and limit %lu",
			query_cache_size, query_cache_limit));
    DBUG_RETURN(0); // in any case we don't have such piece of memory
  }

  /* Free old queries until we have enough memory to store this block */
  Query_cache_block *block;
  do
  {
    block= get_free_block(len, not_less, minimum);
  }
  while (block == 0 && !free_old_query());

  if (block != 0)				// If we found a suitable block
  {
    if (block->length >= ALIGN_SIZE(len) + min_allocation_unit)
      split_block(block,ALIGN_SIZE(len));
  }

  DBUG_RETURN(block);
}


Query_cache_block *
Query_cache::get_free_block(size_t len, my_bool not_less, size_t min)
{
  Query_cache_block *block = 0, *first = 0;
  DBUG_ENTER("Query_cache::get_free_block");
  DBUG_PRINT("qcache",("length %zu, not_less %d, min %zu", len,
		     (int)not_less, min));

  /* Find block with minimal size > len  */
  uint start = find_bin(len);
  // try matching bin
  if (bins[start].number != 0)
  {
    Query_cache_block *list = bins[start].free_blocks;
    if (list->prev->length >= len) // check block with max size
    {
      first = list;
      uint n = 0;
      while ( n < QUERY_CACHE_MEM_BIN_TRY &&
	      first->length < len) //we don't need irst->next != list
      {
	first=first->next;
	n++;
      }
      if (first->length >= len)
	block=first;
      else // we don't need if (first->next != list)
      {
	n = 0;
	block = list->prev;
	while (n < QUERY_CACHE_MEM_BIN_TRY &&
	       block->length > len)
	{
	  block=block->prev;
	  n++;
	}
	if (block->length < len)
	  block=block->next;
      }
    }
    else
      first = list->prev;
  }
  if (block == 0 && start > 0)
  {
    DBUG_PRINT("qcache",("Try bins with bigger block size"));
    // Try more big bins
    int i = start - 1;
    while (i > 0 && bins[i].number == 0)
      i--;
    if (bins[i].number > 0)
      block = bins[i].free_blocks;
  }

  // If no big blocks => try less size (if it is possible)
  if (block == 0 && ! not_less)
  {
    DBUG_PRINT("qcache",("Try to allocate a smaller block"));
    if (first != 0 && first->length > min)
      block = first;
    else
    {
      uint i = start + 1;
      /* bins[mem_bin_num].number contains 1 for easy end test */
      for (i= start+1 ; bins[i].number == 0 ; i++) ;
      if (i < mem_bin_num && bins[i].free_blocks->prev->length >= min)
	block = bins[i].free_blocks->prev;
    }
  }
  if (block != 0)
    exclude_from_free_memory_list(block);

  DBUG_PRINT("qcache",("getting block 0x%lx", (ulong) block));
  DBUG_RETURN(block);
}


void Query_cache::free_memory_block(Query_cache_block *block)
{
  DBUG_ENTER("Query_cache::free_memory_block");
  block->used=0;
  block->type= Query_cache_block::FREE; // mark block as free in any case
  DBUG_PRINT("qcache",
	     ("first_block 0x%lx, block 0x%lx, pnext 0x%lx pprev 0x%lx",
	      (ulong) first_block, (ulong) block, (ulong) block->pnext,
	      (ulong) block->pprev));

  if (block->pnext != first_block && block->pnext->is_free())
    block = join_free_blocks(block, block->pnext);
  if (block != first_block && block->pprev->is_free())
    block = join_free_blocks(block->pprev, block->pprev);
  insert_into_free_memory_list(block);
  DBUG_VOID_RETURN;
}


void Query_cache::split_block(Query_cache_block *block, ulong len)
{
  DBUG_ENTER("Query_cache::split_block");
  Query_cache_block *new_block = (Query_cache_block*)(((uchar*) block)+len);

  new_block->init(block->length - len);
  total_blocks++;
  block->length=len;
  new_block->pnext = block->pnext;
  block->pnext = new_block;
  new_block->pprev = block;
  new_block->pnext->pprev = new_block;

  if (block->type == Query_cache_block::FREE)
  {
    // if block was free then it already joined with all free neighbours
    insert_into_free_memory_list(new_block);
  }
  else
    free_memory_block(new_block);

  DBUG_PRINT("qcache", ("split 0x%lx (%lu) new 0x%lx",
		      (ulong) block, len, (ulong) new_block));
  DBUG_VOID_RETURN;
}


Query_cache_block *
Query_cache::join_free_blocks(Query_cache_block *first_block_arg,
			      Query_cache_block *block_in_list)
{
  Query_cache_block *second_block;
  DBUG_ENTER("Query_cache::join_free_blocks");
  DBUG_PRINT("qcache",
	     ("join first 0x%lx, pnext 0x%lx, in list 0x%lx",
	      (ulong) first_block_arg, (ulong) first_block_arg->pnext,
	      (ulong) block_in_list));

  exclude_from_free_memory_list(block_in_list);
  second_block = first_block_arg->pnext;
  // May be was not free block
  second_block->used=0;
  second_block->destroy();
  total_blocks--;

  first_block_arg->length += second_block->length;
  first_block_arg->pnext = second_block->pnext;
  second_block->pnext->pprev = first_block_arg;

  DBUG_RETURN(first_block_arg);
}


my_bool Query_cache::append_next_free_block(Query_cache_block *block,
					    ulong add_size)
{
  Query_cache_block *next_block = block->pnext;
  DBUG_ENTER("Query_cache::append_next_free_block");
  DBUG_PRINT("enter", ("block 0x%lx, add_size %lu", (ulong) block,
		       add_size));

  if (next_block != first_block && next_block->is_free())
  {
    ulong old_len = block->length;
    exclude_from_free_memory_list(next_block);
    next_block->destroy();
    total_blocks--;

    block->length += next_block->length;
    block->pnext = next_block->pnext;
    next_block->pnext->pprev = block;

    if (block->length > ALIGN_SIZE(old_len + add_size) + min_allocation_unit)
      split_block(block,ALIGN_SIZE(old_len + add_size));
    DBUG_PRINT("exit", ("block was appended"));
    DBUG_RETURN(1);
  }
  DBUG_RETURN(0);
}


void Query_cache::exclude_from_free_memory_list(Query_cache_block *free_block)
{
  DBUG_ENTER("Query_cache::exclude_from_free_memory_list");
  Query_cache_memory_bin *bin = *((Query_cache_memory_bin **)
				  free_block->data());
  double_linked_list_exclude(free_block, &bin->free_blocks);
  bin->number--;
  free_memory-=free_block->length;
  free_memory_blocks--;
  DBUG_PRINT("qcache",("exclude block 0x%lx, bin 0x%lx", (ulong) free_block,
		     (ulong) bin));
  DBUG_VOID_RETURN;
}

void Query_cache::insert_into_free_memory_list(Query_cache_block *free_block)
{
  DBUG_ENTER("Query_cache::insert_into_free_memory_list");
  uint idx = find_bin(free_block->length);
  insert_into_free_memory_sorted_list(free_block, &bins[idx].free_blocks);
  /*
    We have enough memory in block for storing bin reference due to
    min_allocation_unit choice
  */
  Query_cache_memory_bin **bin_ptr = ((Query_cache_memory_bin**)
				      free_block->data());
  *bin_ptr = bins+idx;
  (*bin_ptr)->number++;
  DBUG_PRINT("qcache",("insert block 0x%lx, bin[%d] 0x%lx",
		     (ulong) free_block, idx, (ulong) *bin_ptr));
  DBUG_VOID_RETURN;
}

uint Query_cache::find_bin(size_t size)
{
  DBUG_ENTER("Query_cache::find_bin");
  // Binary search
  int left = 0, right = mem_bin_steps;
  do
  {
    int middle = (left + right) / 2;
    if (steps[middle].size > size)
      left = middle+1;
    else
      right = middle;
  } while (left < right);
  if (left == 0)
  {
    // first bin not subordinate of common rules
    DBUG_PRINT("qcache", ("first bin (# 0), size %zu",size));
    DBUG_RETURN(0);
  }
  uint bin =  steps[left].idx -
    (uint)((size - steps[left].size)/steps[left].increment);

  DBUG_PRINT("qcache", ("bin %u step %u, size %zu step size %lu",
			bin, left, size, steps[left].size));
  DBUG_RETURN(bin);
}


/*****************************************************************************
 Lists management
*****************************************************************************/

void Query_cache::move_to_query_list_end(Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::move_to_query_list_end");
  double_linked_list_exclude(query_block, &queries_blocks);
  double_linked_list_simple_include(query_block, &queries_blocks);
  DBUG_VOID_RETURN;
}


void Query_cache::insert_into_free_memory_sorted_list(Query_cache_block *
						      new_block,
						      Query_cache_block **
						      list)
{
  DBUG_ENTER("Query_cache::insert_into_free_memory_sorted_list");
  /*
     list sorted by size in ascendant order, because we need small blocks
     more frequently than bigger ones
  */

  new_block->used = 0;
  new_block->n_tables = 0;
  new_block->type = Query_cache_block::FREE;

  if (*list == 0)
  {
    *list = new_block->next=new_block->prev=new_block;
    DBUG_PRINT("qcache", ("inserted into empty list"));
  }
  else
  {
    Query_cache_block *point = *list;
    if (point->length >= new_block->length)
    {
      point = point->prev;
      *list = new_block;
    }
    else
    {
      /* Find right position in sorted list to put block */
      while (point->next != *list &&
	     point->next->length < new_block->length)
	point=point->next;
    }
    new_block->prev = point;
    new_block->next = point->next;
    new_block->next->prev = new_block;
    point->next = new_block;
  }
  free_memory+=new_block->length;
  free_memory_blocks++;
  DBUG_VOID_RETURN;
}


void
Query_cache::double_linked_list_simple_include(Query_cache_block *point,
						Query_cache_block **
						list_pointer)
{
  DBUG_ENTER("Query_cache::double_linked_list_simple_include");
  DBUG_PRINT("qcache", ("including block 0x%lx", (ulong) point));
  if (*list_pointer == 0)
    *list_pointer=point->next=point->prev=point;
  else
  {
    // insert to the end of list
    point->next = (*list_pointer);
    point->prev = (*list_pointer)->prev;
    point->prev->next = point;
    (*list_pointer)->prev = point;
  }
  DBUG_VOID_RETURN;
}

void
Query_cache::double_linked_list_exclude(Query_cache_block *point,
					Query_cache_block **list_pointer)
{
  DBUG_ENTER("Query_cache::double_linked_list_exclude");
  DBUG_PRINT("qcache", ("excluding block 0x%lx, list 0x%lx",
		      (ulong) point, (ulong) list_pointer));
  if (point->next == point)
    *list_pointer = 0;				// empty list
  else
  {
    point->next->prev = point->prev;
    point->prev->next = point->next;
    /*
       If the root is removed; select a new root
    */
    if (point == *list_pointer)
      *list_pointer= point->next;
  }
  DBUG_VOID_RETURN;
}


void Query_cache::double_linked_list_join(Query_cache_block *head_tail,
					  Query_cache_block *tail_head)
{
  Query_cache_block *head_head = head_tail->next,
		    *tail_tail	= tail_head->prev;
  head_head->prev = tail_tail;
  head_tail->next = tail_head;
  tail_head->prev = head_tail;
  tail_tail->next = head_head;
}

/*****************************************************************************
 Query
*****************************************************************************/

/*
  Collect information about table types, check that tables are cachable and
  count them

  SYNOPSIS
    process_and_count_tables()
    tables_used     table list for processing
    tables_type     pointer to variable for table types collection

  RETURN
    0   error
    >0  number of tables
*/

TABLE_COUNTER_TYPE
Query_cache::process_and_count_tables(THD *thd, TABLE_LIST *tables_used,
                                      uint8 *tables_type)
{
  DBUG_ENTER("process_and_count_tables");
  TABLE_COUNTER_TYPE table_count = 0;
  for (; tables_used; tables_used= tables_used->next_global)
  {
    table_count++;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
    /*
      Disable any attempt to store this statement if there are
      column level grants on any referenced tables.
      The grant.want_privileges flag was set to 1 in the
      check_grant() function earlier if the TABLE_LIST object
      had any associated column privileges.

      We need to check that the TABLE_LIST object isn't part
      of a VIEW definition because we want to be able to cache
      views.

      Tables underlying a MERGE table does not have useful privilege
      information in their grant objects, so skip these tables from the test.
    */
    if (tables_used->belong_to_view == NULL &&
        (!tables_used->parent_l ||
         tables_used->parent_l->table->file->ht->db_type != DB_TYPE_MRG_MYISAM))
    {
      assert((SELECT_ACL & ~tables_used->grant.privilege) ==
             tables_used->grant.want_privilege);
      if ((tables_used->grant.privilege & SELECT_ACL) == 0)
      {
        DBUG_PRINT("qcache", ("Don't cache statement as it refers to "
                              "tables with column privileges."));
        thd->lex->safe_to_cache_query= 0;
        DBUG_RETURN(0);
      }
    }
#endif
    if (tables_used->is_view())
    {
      DBUG_PRINT("qcache", ("view: %s  db: %s",
                            tables_used->view_name.str,
                            tables_used->view_db.str));
      *tables_type|= HA_CACHE_TBL_NONTRANSACT;
    }
    else
    {
      if (tables_used->is_derived())
      {
        DBUG_PRINT("qcache", ("table: %s", tables_used->alias));
        table_count--;
        DBUG_PRINT("qcache", ("derived table skipped"));
        continue;
      }
      DBUG_PRINT("qcache", ("table: %s  db:  %s  type: %u",
                            tables_used->table->s->table_name.str,
                            tables_used->table->s->db.str,
                            tables_used->table->s->db_type()->db_type));
      *tables_type|= tables_used->table->file->table_cache_type();

      /*
        table_alias_charset used here because it depends of
        lower_case_table_names variable
      */
      if (tables_used->table->s->tmp_table != NO_TMP_TABLE ||
          (*tables_type & HA_CACHE_TBL_NOCACHE) ||
          (tables_used->db_length == 5 &&
           my_strnncoll(table_alias_charset,
                        (uchar*)tables_used->table->s->table_cache_key.str, 6,
                        (uchar*)"mysql",6) == 0))
      {
        DBUG_PRINT("qcache",
                   ("select not cacheable: temporary, system or "
                    "other non-cacheable table(s)"));
        DBUG_RETURN(0);
      }
      /*
        XXX FIXME: Some generic mechanism is required here instead of this
        MYISAMMRG-specific implementation.
      */
      if (tables_used->table->s->db_type()->db_type == DB_TYPE_MRG_MYISAM)
      {
        ha_myisammrg *handler = (ha_myisammrg *)tables_used->table->file;
        MYRG_INFO *file = handler->myrg_info();
        table_count+= (file->end_table - file->open_tables);
      }
    }
  }
  DBUG_RETURN(table_count);
}


/*
  If query is cacheable return number tables in query
  (query without tables are not cached)
*/

TABLE_COUNTER_TYPE
Query_cache::is_cacheable(THD *thd, LEX *lex,
                          TABLE_LIST *tables_used, uint8 *tables_type)
{
  TABLE_COUNTER_TYPE table_count;
  DBUG_ENTER("Query_cache::is_cacheable");

  if (lex->sql_command == SQLCOM_SELECT &&
      lex->safe_to_cache_query &&
      !lex->describe &&
      (thd->variables.query_cache_type == 1 ||
       (thd->variables.query_cache_type == 2 &&
        (lex->select_lex->active_options() & OPTION_TO_QUERY_CACHE))))
  {
    DBUG_PRINT("qcache", ("options: %lx  %lx  type: %u",
                          (long) OPTION_TO_QUERY_CACHE,
                          (long) lex->select_lex->active_options(),
                          (int) thd->variables.query_cache_type));

    if (!(table_count= process_and_count_tables(thd, tables_used,
                                                tables_type)))
      DBUG_RETURN(0);

    if (thd->in_multi_stmt_transaction_mode() &&
	((*tables_type)&HA_CACHE_TBL_TRANSACT))
    {
      DBUG_PRINT("qcache", ("not in autocommin mode"));
      DBUG_RETURN(0);
    }
    DBUG_PRINT("qcache", ("select is using %zu tables", table_count));
    DBUG_RETURN(table_count);
  }

  DBUG_PRINT("qcache",
	     ("not interesting query: %d or not cacheable, options %lx %lx  type: %u",
	      (int) lex->sql_command,
	      (long) OPTION_TO_QUERY_CACHE,
	      (long) lex->select_lex->active_options(),
	      (int) thd->variables.query_cache_type));
  DBUG_RETURN(0);
}

/*
  Check handler allowance to cache query with these tables

  SYNOPSYS
    Query_cache::ask_handler_allowance()
    thd - thread handlers
    tables_used - tables list used in query

  RETURN
    0 - caching allowed
    1 - caching disallowed
*/
my_bool Query_cache::ask_handler_allowance(THD *thd,
					   TABLE_LIST *tables_used)
{
  DBUG_ENTER("Query_cache::ask_handler_allowance");

  for (; tables_used; tables_used= tables_used->next_global)
  {
    TABLE *table;
    handler *handler;
    if (!(table= tables_used->table))
      continue;
    handler= table->file;
    // Allow caching of queries with materialized derived tables or views
    if (tables_used->uses_materialization())
    {
      /*
        Skip the derived table itself, but process its underlying tables and
        other tables that follow.
      */
      continue;
    }

    /*
      @todo: I think this code can be skipped, anyway it is dead now!
      We're skipping a special case here (MERGE VIEW on top of a TEMPTABLE
      view). This is MyISAMly safe because we know it's not a user-created
      TEMPTABLE as those are guarded against in
      Query_cache::process_and_count_tables(), and schema-tables clear
      safe_to_cache_query. This implies that nobody else will change our
      TEMPTABLE while we're using it, so calling register_query_cache_table()
      in MyISAM to check on it is pointless. Finally, we should see the
      TEMPTABLE view again in a subsequent iteration, anyway.
    */
    if (tables_used->is_view() && tables_used->is_merged() &&
        table->s->get_table_ref_type() == TABLE_REF_TMP_TABLE)
    {
      assert(false);
      continue;
    }
    if (!handler->register_query_cache_table(thd,
                                             table->s->normalized_path.str,
                                             table->s->normalized_path.length,
                                             &tables_used->callback_func,
                                             &tables_used->engine_data))
    {
      DBUG_PRINT("qcache", ("Handler does not allow caching for %s.%s",
                            tables_used->db, tables_used->alias));
      thd->lex->safe_to_cache_query= 0;          // Don't try to cache this
      DBUG_RETURN(1);
    }
  }
  DBUG_RETURN(0);
}


/*****************************************************************************
  Packing
*****************************************************************************/


/**
  Rearrange all memory blocks so that free memory joins at the
  'bottom' of the allocated memory block containing all cache data.
  @see Query_cache::pack(ulong join_limit, uint iteration_limit)
*/

void Query_cache::pack_cache()
{
  DBUG_ENTER("Query_cache::pack_cache");

  DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););

  uchar *border = 0;
  Query_cache_block *before = 0;
  ulong gap = 0;
  my_bool ok = 1;
  Query_cache_block *block = first_block;
  DUMP(this);

  if (first_block)
  {
    do
    {
      Query_cache_block *next=block->pnext;
      ok = move_by_type(&border, &before, &gap, block);
      block = next;
    } while (ok && block != first_block);

    if (border != 0)
    {
      Query_cache_block *new_block = (Query_cache_block *) border;
      new_block->init(gap);
      total_blocks++;
      new_block->pnext = before->pnext;
      before->pnext = new_block;
      new_block->pprev = before;
      new_block->pnext->pprev = new_block;
      insert_into_free_memory_list(new_block);
    }
    DUMP(this);
  }

  DBUG_EXECUTE("check_querycache", check_integrity(CALLER_HOLDS_LOCK););
  DBUG_VOID_RETURN;
}


my_bool Query_cache::move_by_type(uchar **border,
				  Query_cache_block **before, ulong *gap,
				  Query_cache_block *block)
{
  DBUG_ENTER("Query_cache::move_by_type");

  my_bool ok = 1;
  switch (block->type) {
  case Query_cache_block::FREE:
  {
    DBUG_PRINT("qcache", ("block 0x%lx FREE", (ulong) block));
    if (*border == 0)
    {
      *border = (uchar *) block;
      *before = block->pprev;
      DBUG_PRINT("qcache", ("gap beginning here"));
    }
    exclude_from_free_memory_list(block);
    *gap +=block->length;
    block->pprev->pnext=block->pnext;
    block->pnext->pprev=block->pprev;
    block->destroy();
    total_blocks--;
    DBUG_PRINT("qcache", ("added to gap (%lu)", *gap));
    break;
  }
  case Query_cache_block::TABLE:
  {
    HASH_SEARCH_STATE record_idx;
    DBUG_PRINT("qcache", ("block 0x%lx TABLE", (ulong) block));
    if (*border == 0)
      break;
    ulong len = block->length, used = block->used;
    Query_cache_block_table *list_root = block->table(0);
    Query_cache_block_table *tprev = list_root->prev,
			    *tnext = list_root->next;
    Query_cache_block *prev = block->prev,
		      *next = block->next,
		      *pprev = block->pprev,
		      *pnext = block->pnext,
		      *new_block =(Query_cache_block *) *border;
    size_t tablename_offset = block->table()->table() - block->table()->db();
    char *data = (char*) block->data();
    uchar *key;
    size_t key_length;
    key=query_cache_table_get_key((uchar*) block, &key_length, 0);
    my_hash_first(&tables, key, key_length, &record_idx);

    block->destroy();
    new_block->init(len);
    new_block->type=Query_cache_block::TABLE;
    new_block->used=used;
    new_block->n_tables=1;
    memmove((char*) new_block->data(), data, len-new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    if (tables_blocks == block)
      tables_blocks = new_block;

    Query_cache_block_table *nlist_root = new_block->table(0);
    nlist_root->n = 0;
    nlist_root->next = tnext;
    tnext->prev = nlist_root;
    nlist_root->prev = tprev;
    tprev->next = nlist_root;
    DBUG_PRINT("qcache",
	       ("list_root: 0x%lx tnext 0x%lx tprev 0x%lx tprev->next 0x%lx tnext->prev 0x%lx",
		(ulong) list_root, (ulong) tnext, (ulong) tprev,
		(ulong)tprev->next, (ulong)tnext->prev));
    /*
      Go through all queries that uses this table and change them to
      point to the new table object
    */
    Query_cache_table *new_block_table=new_block->table();
    for (;tnext != nlist_root; tnext=tnext->next)
      tnext->parent= new_block_table;
    *border += len;
    *before = new_block;
    /* Fix pointer to table name */
    new_block->table()->table(new_block->table()->db() + tablename_offset);
    /* Fix hash to point at moved block */
    my_hash_replace(&tables, &record_idx, (uchar*) new_block);

    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  case Query_cache_block::QUERY:
  {
    HASH_SEARCH_STATE record_idx;
    DBUG_PRINT("qcache", ("block 0x%lx QUERY", (ulong) block));
    if (*border == 0)
      break;
    BLOCK_LOCK_WR(block);
    ulong len = block->length, used = block->used;
    TABLE_COUNTER_TYPE n_tables = block->n_tables;
    Query_cache_block	*prev = block->prev,
			*next = block->next,
			*pprev = block->pprev,
			*pnext = block->pnext,
			*new_block =(Query_cache_block*) *border;
    char *data = (char*) block->data();
    Query_cache_block *first_result_block = ((Query_cache_query *)
					     block->data())->result();
    uchar *key;
    size_t key_length;
    key=query_cache_query_get_key((uchar*) block, &key_length, 0);
    my_hash_first(&queries, key, key_length, &record_idx);
    // Move table of used tables
    memmove((char*) new_block->table(0), (char*) block->table(0),
	   ALIGN_SIZE(n_tables*sizeof(Query_cache_block_table)));
    block->query()->unlock_n_destroy();
    block->destroy();
    new_block->init(len);
    new_block->type=Query_cache_block::QUERY;
    new_block->used=used;
    new_block->n_tables=n_tables;
    memmove((char*) new_block->data(), data, len - new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    if (queries_blocks == block)
      queries_blocks = new_block;
    Query_cache_block_table *beg_of_table_table= block->table(0),
      *end_of_table_table= block->table(n_tables);
    uchar *beg_of_new_table_table= (uchar*) new_block->table(0);

    for (TABLE_COUNTER_TYPE j=0; j < n_tables; j++)
    {
      Query_cache_block_table *block_table = new_block->table(j);

      // use aligment from begining of table if 'next' is in same block
      if ((beg_of_table_table <= block_table->next) &&
	  (block_table->next < end_of_table_table))
	((Query_cache_block_table *)(beg_of_new_table_table +
				     (((uchar*)block_table->next) -
				      ((uchar*)beg_of_table_table))))->prev=
	 block_table;
      else
	block_table->next->prev= block_table;

      // use aligment from begining of table if 'prev' is in same block
      if ((beg_of_table_table <= block_table->prev) &&
	  (block_table->prev < end_of_table_table))
	((Query_cache_block_table *)(beg_of_new_table_table +
				     (((uchar*)block_table->prev) -
				      ((uchar*)beg_of_table_table))))->next=
	  block_table;
      else
	block_table->prev->next = block_table;
    }
    DBUG_PRINT("qcache", ("after circle tt"));
    *border += len;
    *before = new_block;
    new_block->query()->result(first_result_block);
    if (first_result_block != 0)
    {
      Query_cache_block *result_block = first_result_block;
      do
      {
	result_block->result()->parent(new_block);
	result_block = result_block->next;
      } while ( result_block != first_result_block );
    }
    Query_cache_query *new_query= ((Query_cache_query *) new_block->data());
    mysql_rwlock_init(key_rwlock_query_cache_query_lock, &new_query->lock);

    /*
      If someone is writing to this block, inform the writer that the block
      has been moved.
    */
    Query_cache_tls *query_cache_tls= new_block->query()->writer();
    if (query_cache_tls != NULL)
    {
      query_cache_tls->first_query_block= new_block;
    }
    /* Fix hash to point at moved block */
    my_hash_replace(&queries, &record_idx, (uchar*) new_block);
    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  case Query_cache_block::RES_INCOMPLETE:
  case Query_cache_block::RES_BEG:
  case Query_cache_block::RES_CONT:
  case Query_cache_block::RESULT:
  {
    DBUG_PRINT("qcache", ("block 0x%lx RES* (%d)", (ulong) block,
               (int) block->type));
    if (*border == 0)
      break;
    Query_cache_block *query_block= block->result()->parent();
    BLOCK_LOCK_WR(query_block);
    Query_cache_block *next= block->next, *prev= block->prev;
    Query_cache_block::block_type type= block->type;
    ulong len = block->length, used = block->used;
    Query_cache_block *pprev = block->pprev,
		      *pnext = block->pnext,
		      *new_block =(Query_cache_block*) *border;
    char *data = (char*) block->data();
    block->destroy();
    new_block->init(len);
    new_block->type=type;
    new_block->used=used;
    memmove((char*) new_block->data(), data, len - new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    new_block->result()->parent(query_block);
    Query_cache_query *query = query_block->query();
    if (query->result() == block)
      query->result(new_block);
    *border += len;
    *before = new_block;
    /* If result writing complete && we have free space in block */
    ulong free_space= new_block->length - new_block->used;
    free_space-= free_space % ALIGN_SIZE(1);
    if (query->result()->type == Query_cache_block::RESULT &&
	new_block->length > new_block->used &&
	*gap + free_space > min_allocation_unit &&
	new_block->length - free_space > min_allocation_unit)
    {
      *border-= free_space;
      *gap+= free_space;
      DBUG_PRINT("qcache",
		 ("rest of result free space added to gap (%lu)", *gap));
      new_block->length -= free_space;
    }
    BLOCK_UNLOCK_WR(query_block);
    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  default:
    DBUG_PRINT("error", ("unexpected block type %d, block 0x%lx",
			 (int)block->type, (ulong) block));
    ok = 0;
  }
  DBUG_RETURN(ok);
}


void Query_cache::relink(Query_cache_block *oblock,
			 Query_cache_block *nblock,
			 Query_cache_block *next, Query_cache_block *prev,
			 Query_cache_block *pnext, Query_cache_block *pprev)
{
  if (prev == oblock) //check pointer to himself
  {
    nblock->prev = nblock;
    nblock->next = nblock;
  }
  else
  {
    nblock->prev = prev;
    prev->next=nblock;
  }
  if (next != oblock)
  {
    nblock->next = next;
    next->prev=nblock;
  }
  nblock->pprev = pprev; // Physical pointer to himself have only 1 free block
  nblock->pnext = pnext;
  pprev->pnext=nblock;
  pnext->pprev=nblock;
}


my_bool Query_cache::join_results(ulong join_limit)
{
  my_bool has_moving = 0;
  DBUG_ENTER("Query_cache::join_results");

  if (queries_blocks != 0)
  {
    assert(query_cache_size > 0);
    Query_cache_block *block = queries_blocks;
    do
    {
      Query_cache_query *header = block->query();
      if (header->result() != 0 &&
	  header->result()->type == Query_cache_block::RESULT &&
	  header->length() > join_limit)
      {
	Query_cache_block *new_result_block =
	  get_free_block(ALIGN_SIZE(header->length()) +
			 ALIGN_SIZE(sizeof(Query_cache_block)) +
			 ALIGN_SIZE(sizeof(Query_cache_result)), 1, 0);
	if (new_result_block != 0)
	{
	  has_moving = 1;
	  Query_cache_block *first_result = header->result();
	  ulong new_len = (header->length() +
			   ALIGN_SIZE(sizeof(Query_cache_block)) +
			   ALIGN_SIZE(sizeof(Query_cache_result)));
	  if (new_result_block->length >
	      ALIGN_SIZE(new_len) + min_allocation_unit)
	    split_block(new_result_block, ALIGN_SIZE(new_len));
	  BLOCK_LOCK_WR(block);
	  header->result(new_result_block);
	  new_result_block->type = Query_cache_block::RESULT;
	  new_result_block->n_tables = 0;
	  new_result_block->used = new_len;

	  new_result_block->next = new_result_block->prev = new_result_block;
	  DBUG_PRINT("qcache", ("new block %lu/%lu (%lu)",
			      new_result_block->length,
			      new_result_block->used,
			      header->length()));

	  Query_cache_result *new_result = new_result_block->result();
	  new_result->parent(block);
	  uchar *write_to = new_result->data();
	  Query_cache_block *result_block = first_result;
	  do
	  {
	    ulong len = (result_block->used - result_block->headers_len() -
			 ALIGN_SIZE(sizeof(Query_cache_result)));
	    DBUG_PRINT("loop", ("add block %lu/%lu (%lu)",
				result_block->length,
				result_block->used,
				len));
	    memcpy((char *) write_to,
		   (char*) result_block->result()->data(),
		   len);
	    write_to += len;
	    Query_cache_block *old_result_block = result_block;
	    result_block = result_block->next;
	    free_memory_block(old_result_block);
	  } while (result_block != first_result);
	  BLOCK_UNLOCK_WR(block);
	}
      }
      block = block->next;
    } while ( block != queries_blocks );
  }
  DBUG_RETURN(has_moving);
}


size_t Query_cache::filename_2_table_key (char *key, const char *path,
                                          size_t *db_length)
{
  char tablename[FN_REFLEN+2], *filename, *dbname;
  DBUG_ENTER("Query_cache::filename_2_table_key");

  /* Safety if filename didn't have a directory name */
  tablename[0]= FN_LIBCHAR;
  tablename[1]= FN_LIBCHAR;
  /* Convert filename to this OS's format in tablename */
  fn_format(tablename + 2, path, "", "", MY_REPLACE_EXT);
  filename=  tablename + dirname_length(tablename + 2) + 2;
  /* Find start of databasename */
  for (dbname= filename - 2 ; dbname[-1] != FN_LIBCHAR ; dbname--) ;
  *db_length= (filename - dbname) - 1;
  DBUG_PRINT("qcache", ("table '%-.*s.%s'", static_cast<int>(*db_length), dbname, filename));

  DBUG_RETURN(static_cast<size_t>(strmake(strmake(key, dbname,
                                                  min<size_t>(*db_length,
                                                              NAME_LEN)) + 1,
                                  filename, NAME_LEN) - key) + 1);
}

/****************************************************************************
  Functions to be used when debugging
****************************************************************************/

#if defined(NDEBUG) || !defined(EXTRA_DEBUG)

void Query_cache::wreck(uint line, const char *message) { query_cache_size = 0; }
void Query_cache::bins_dump() {}
void Query_cache::cache_dump() {}
void Query_cache::queries_dump() {}
void Query_cache::tables_dump() {}
bool Query_cache::check_integrity(enum_qcci_lock_mode locking) { return false; }
my_bool Query_cache::in_list(Query_cache_block *root, Query_cache_block *point,
                             const char *name) { return 0;}
my_bool Query_cache::in_blocks(Query_cache_block * point) { return 0; }

#else


/*
  Debug method which switch query cache off but left content for
  investigation.

  SYNOPSIS
    Query_cache::wreck()
    line                 line of the wreck() call
    message              message for logging
*/

void Query_cache::wreck(uint line, const char *message)
{
  THD *thd=current_thd;
  DBUG_ENTER("Query_cache::wreck");
  query_cache_size = 0;
  if (*message)
    DBUG_PRINT("error", (" %s", message));
  DBUG_PRINT("warning", ("=================================="));
  DBUG_PRINT("warning", ("%5d QUERY CACHE WRECK => DISABLED",line));
  DBUG_PRINT("warning", ("=================================="));
  if (thd)
    thd->killed= THD::KILL_CONNECTION;
  cache_dump();
  bins_dump();
  DBUG_VOID_RETURN;
}


void Query_cache::bins_dump()
{
  uint i;

  if (!initialized || query_cache_size == 0)
  {
    DBUG_PRINT("qcache", ("Query Cache not initialized"));
    return;
  }

  DBUG_PRINT("qcache", ("mem_bin_num=%u, mem_bin_steps=%u",
		      mem_bin_num, mem_bin_steps));
  DBUG_PRINT("qcache", ("-------------------------"));
  DBUG_PRINT("qcache", ("      size idx       step"));
  DBUG_PRINT("qcache", ("-------------------------"));
  for (i=0; i < mem_bin_steps; i++)
  {
    DBUG_PRINT("qcache", ("%10lu %3d %10lu", steps[i].size, steps[i].idx,
			steps[i].increment));
  }
  DBUG_PRINT("qcache", ("-------------------------"));
  DBUG_PRINT("qcache", ("      size num"));
  DBUG_PRINT("qcache", ("-------------------------"));
  for (i=0; i < mem_bin_num; i++)
  {
    DBUG_PRINT("qcache", ("%10lu %3d 0x%lx", bins[i].size, bins[i].number,
			(ulong)&(bins[i])));
    if (bins[i].free_blocks)
    {
      Query_cache_block *block = bins[i].free_blocks;
      do{
	DBUG_PRINT("qcache", ("\\-- %lu 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
			    block->length, (ulong)block,
			    (ulong)block->next, (ulong)block->prev,
			    (ulong)block->pnext, (ulong)block->pprev));
	block = block->next;
      } while ( block != bins[i].free_blocks );
    }
  }
  DBUG_PRINT("qcache", ("-------------------------"));
}


void Query_cache::cache_dump()
{
  if (!initialized || query_cache_size == 0)
  {
    DBUG_PRINT("qcache", ("Query Cache not initialized"));
    return;
  }

  DBUG_PRINT("qcache", ("-------------------------------------"));
  DBUG_PRINT("qcache", ("    length       used t nt"));
  DBUG_PRINT("qcache", ("-------------------------------------"));
  Query_cache_block *i = first_block;
  do
  {
    DBUG_PRINT("qcache",
	       ("%10lu %10lu %1d %2d 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
		i->length, i->used, (int)i->type,
		i->n_tables, (ulong)i,
		(ulong)i->next, (ulong)i->prev, (ulong)i->pnext,
		(ulong)i->pprev));
    i = i->pnext;
  } while ( i != first_block );
  DBUG_PRINT("qcache", ("-------------------------------------"));
}


void Query_cache::queries_dump()
{

  if (!initialized)
  {
    DBUG_PRINT("qcache", ("Query Cache not initialized"));
    return;
  }

  DBUG_PRINT("qcache", ("------------------"));
  DBUG_PRINT("qcache", (" QUERIES"));
  DBUG_PRINT("qcache", ("------------------"));
  if (queries_blocks != 0)
  {
    Query_cache_block *block = queries_blocks;
    do
    {
      size_t len;
      char *str = (char*) query_cache_query_get_key((uchar*) block, &len, 0);
      len-= QUERY_CACHE_FLAGS_SIZE;		  // Point at flags
      Query_cache_query_flags flags;
      memcpy(&flags, str+len, QUERY_CACHE_FLAGS_SIZE);
      str[len]= 0; // make zero ending DB name
      DBUG_PRINT("qcache", ("F: %u  C: %u L: %lu  T: '%s' (%lu)  '%s'  '%s'",
			    flags.client_long_flag,
			    flags.character_set_client_num,
                            (ulong)flags.limit,
                            flags.time_zone->get_name()->ptr(),
			    (ulong) len, str, strend(str)+1));
      DBUG_PRINT("qcache", ("-b- 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx", (ulong) block,
			    (ulong) block->next, (ulong) block->prev,
			    (ulong)block->pnext, (ulong)block->pprev));
      memcpy(str + len, &flags, QUERY_CACHE_FLAGS_SIZE); // restore flags
      for (TABLE_COUNTER_TYPE t= 0; t < block->n_tables; t++)
      {
	Query_cache_table *table= block->table(t)->parent;
	DBUG_PRINT("qcache", ("-t- '%s' '%s'", table->db(), table->table()));
      }
      Query_cache_query *header = block->query();
      if (header->result())
      {
	Query_cache_block *result_block = header->result();
	Query_cache_block *result_beg = result_block;
	do
	{
	  DBUG_PRINT("qcache", ("-r- %u %lu/%lu 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
			      (uint) result_block->type,
			      result_block->length, result_block->used,
			      (ulong) result_block,
			      (ulong) result_block->next,
			      (ulong) result_block->prev,
			      (ulong) result_block->pnext,
			      (ulong) result_block->pprev));
	  result_block = result_block->next;
	} while ( result_block != result_beg );
      }
    } while ((block=block->next) != queries_blocks);
  }
  else
  {
    DBUG_PRINT("qcache", ("no queries in list"));
  }
  DBUG_PRINT("qcache", ("------------------"));
}


void Query_cache::tables_dump()
{
  if (!initialized || query_cache_size == 0)
  {
    DBUG_PRINT("qcache", ("Query Cache not initialized"));
    return;
  }

  DBUG_PRINT("qcache", ("--------------------"));
  DBUG_PRINT("qcache", ("TABLES"));
  DBUG_PRINT("qcache", ("--------------------"));
  if (tables_blocks != 0)
  {
    Query_cache_block *table_block = tables_blocks;
    do
    {
      Query_cache_table *table = table_block->table();
      DBUG_PRINT("qcache", ("'%s' '%s'", table->db(), table->table()));
      table_block = table_block->next;
    } while (table_block != tables_blocks);
  }
  else
    DBUG_PRINT("qcache", ("no tables in list"));
  DBUG_PRINT("qcache", ("--------------------"));
}


/**
  Checks integrity of the various linked lists

  @param locking  CALLER_HOLDS_LOCK | LOCK_WHILE_CHECKING  Who does locking?

  @return Error status code
    @retval false Query cache is operational.
    @retval true  Query cache is broken.
*/

bool Query_cache::check_integrity(enum_qcci_lock_mode locking)
{
  bool result= false;
  uint i;

  DBUG_ENTER("check_integrity");

  /*
    If we can't get a lock here, it means someone's throwing out the cache so
    there's nothing to check, anyway, so that's OK.
  */
  if ((locking == LOCK_WHILE_CHECKING) && (try_lock()))
    DBUG_RETURN(false);

  if (my_hash_check(&queries))
  {
    DBUG_PRINT("error", ("queries hash is damaged"));
    result= true;
  }

  if (my_hash_check(&tables))
  {
    DBUG_PRINT("error", ("tables hash is damaged"));
    result= true;
  }

  DBUG_PRINT("qcache", ("physical address check ..."));
  ulong free=0, used=0;
  Query_cache_block * block = first_block;
  do
  {
    /* When checking at system start, there is no block. */
    if (!block)
      break;

    DBUG_PRINT("qcache", ("block 0x%lx, type %u...",
			  (ulong) block, (uint) block->type));
    // Check allignment
    if ((((long)block) % (long) ALIGN_SIZE(1)) !=
	(((long)first_block) % (long)ALIGN_SIZE(1)))
    {
      DBUG_PRINT("error",
		 ("block 0x%lx do not aligned by %d", (ulong) block,
		  (int) ALIGN_SIZE(1)));
      result= true;
    }
    // Check memory allocation
    if (block->pnext == first_block) // Is it last block?
    {
      if (((uchar*)block) + block->length !=
	  ((uchar*)first_block) + query_cache_size)
      {
	DBUG_PRINT("error",
		   ("block 0x%lx, type %u, ended at 0x%lx, but cache ended at 0x%lx",
		    (ulong) block, (uint) block->type,
		    (ulong) (((uchar*)block) + block->length),
		    (ulong) (((uchar*)first_block) + query_cache_size)));
	result= true;
      }
    }
    else
      if (((uchar*)block) + block->length != ((uchar*)block->pnext))
      {
	DBUG_PRINT("error",
		   ("block 0x%lx, type %u, ended at 0x%lx, but next block begining at 0x%lx",
		    (ulong) block, (uint) block->type,
		    (ulong) (((uchar*)block) + block->length),
		    (ulong) ((uchar*)block->pnext)));
      }
    if (block->type == Query_cache_block::FREE)
      free+= block->length;
    else
      used+= block->length;
    switch(block->type) {
    case Query_cache_block::FREE:
    {
      Query_cache_memory_bin *bin = *((Query_cache_memory_bin **)
				      block->data());
      //is it correct pointer?
      if (((uchar*)bin) < ((uchar*)bins) ||
	  ((uchar*)bin) >= ((uchar*)first_block))
      {
	DBUG_PRINT("error",
		   ("free block 0x%lx have bin pointer 0x%lx beyaond of bins array bounds [0x%lx,0x%lx]",
		    (ulong) block,
		    (ulong) bin,
		    (ulong) bins,
		    (ulong) first_block));
	result= true;
      }
      else
      {
	int idx = (((uchar*)bin) - ((uchar*)bins)) /
	  sizeof(Query_cache_memory_bin);
	if (in_list(bins[idx].free_blocks, block, "free memory"))
	  result= true;
      }
      break;
    }
    case Query_cache_block::TABLE:
      if (in_list(tables_blocks, block, "tables"))
        result= true;
      if (in_table_list(block->table(0),  block->table(0), "table list root"))
        result= true;
      break;
    case Query_cache_block::QUERY:
    {
      if (in_list(queries_blocks, block, "query"))
        result = true;
      for (TABLE_COUNTER_TYPE j=0; j < block->n_tables; j++)
      {
	Query_cache_block_table *block_table = block->table(j);
	Query_cache_block_table *block_table_root =
	  (Query_cache_block_table *)
	  (((uchar*)block_table->parent) -
	   ALIGN_SIZE(sizeof(Query_cache_block_table)));

        if (in_table_list(block_table, block_table_root, "table list"))
          result= true;
      }
      break;
    }
    case Query_cache_block::RES_INCOMPLETE:
      // This type of block can be not lincked yet (in multithread environment)
      break;
    case Query_cache_block::RES_BEG:
    case Query_cache_block::RES_CONT:
    case Query_cache_block::RESULT:
    {
      Query_cache_block * query_block = block->result()->parent();
      if (((uchar*)query_block) < ((uchar*)first_block) ||
	  ((uchar*)query_block) >= (((uchar*)first_block) + query_cache_size))
      {
	DBUG_PRINT("error",
		   ("result block 0x%lx have query block pointer 0x%lx beyaond of block pool bounds [0x%lx,0x%lx]",
		    (ulong) block,
		    (ulong) query_block,
		    (ulong) first_block,
		    (ulong) (((uchar*)first_block) + query_cache_size)));
	result= true;
      }
      else
      {
	BLOCK_LOCK_RD(query_block);
	if (in_list(queries_blocks, query_block, "query from results"))
	  result= true;
	if (in_list(query_block->query()->result(), block,
		    "results"))
	  result= true;
	BLOCK_UNLOCK_RD(query_block);
      }
      break;
    }
    default:
      DBUG_PRINT("error", ("block 0x%lx have incorrect type %u",
                           (long) block, block->type));
      result= true;
    }

    block = block->pnext;
  } while (block != first_block);

  if (used + free != query_cache_size)
  {
    DBUG_PRINT("error",
	       ("used memory (%lu) + free memory (%lu) !=  query_cache_size (%lu)",
		used, free, query_cache_size));
    result= true;
  }

  if (free != free_memory)
  {
    DBUG_PRINT("error",
	       ("free memory (%lu) != free_memory (%lu)",
		free, free_memory));
    result= true;
  }

  DBUG_PRINT("qcache", ("check queries ..."));
  if ((block = queries_blocks))
  {
    do
    {
      DBUG_PRINT("qcache", ("block 0x%lx, type %u...",
			    (ulong) block, (uint) block->type));
      size_t length;
      uchar *key = query_cache_query_get_key((uchar*) block, &length, 0);
      uchar* val = my_hash_search(&queries, key, length);
      if (((uchar*)block) != val)
      {
	DBUG_PRINT("error", ("block 0x%lx found in queries hash like 0x%lx",
			     (ulong) block, (ulong) val));
      }
      if (in_blocks(block))
        result= true;
      Query_cache_block * results = block->query()->result();
      if (results)
      {
	Query_cache_block * result_block = results;
	do
	{
	  DBUG_PRINT("qcache", ("block 0x%lx, type %u...",
				(ulong) block, (uint) block->type));
	  if (in_blocks(result_block))
	    result= true;

	  result_block = result_block->next;
	} while (result_block != results);
      }
      block = block->next;
    } while (block != queries_blocks);
  }

  DBUG_PRINT("qcache", ("check tables ..."));
  if ((block = tables_blocks))
  {
    do
    {
      DBUG_PRINT("qcache", ("block 0x%lx, type %u...",
			    (ulong) block, (uint) block->type));
      size_t length;
      uchar *key = query_cache_table_get_key((uchar*) block, &length, 0);
      uchar* val = my_hash_search(&tables, key, length);
      if (((uchar*)block) != val)
      {
	DBUG_PRINT("error", ("block 0x%lx found in tables hash like 0x%lx",
			     (ulong) block, (ulong) val));
      }

      if (in_blocks(block))
        result= true;
      block=block->next;
    } while (block != tables_blocks);
  }

  DBUG_PRINT("qcache", ("check free blocks"));
  for (i = 0; i < mem_bin_num; i++)
  {
    if ((block = bins[i].free_blocks))
    {
      uint count = 0;
      do
      {
	DBUG_PRINT("qcache", ("block 0x%lx, type %u...",
			      (ulong) block, (uint) block->type));
	if (in_blocks(block))
	  result= true;

	count++;
	block=block->next;
      } while (block != bins[i].free_blocks);
      if (count != bins[i].number)
      {
	DBUG_PRINT("error", ("bins[%d].number= %d, but bin have %d blocks",
			     i, bins[i].number,  count));
	result= true;
      }
    }
  }
  assert(result == 0);

  if (locking == LOCK_WHILE_CHECKING)
    unlock();

  DBUG_RETURN(result);
}


my_bool Query_cache::in_blocks(Query_cache_block * point)
{
  my_bool result = 0;
  Query_cache_block *block = point;
  //back
  do
  {
    if (block->pprev->pnext != block)
    {
      DBUG_PRINT("error",
		 ("block 0x%lx in physical list is incorrect linked, prev block 0x%lx refered as next to 0x%lx (check from 0x%lx)",
		  (ulong) block, (ulong) block->pprev,
		  (ulong) block->pprev->pnext,
		  (ulong) point));
      //back trace
      for (; block != point; block = block->pnext)
	    DBUG_PRINT("error", ("back trace 0x%lx", (ulong) block));
      result = 1;
      goto err1;
    }
    block = block->pprev;
  } while (block != first_block && block != point);
  if (block != first_block)
  {
    DBUG_PRINT("error",
	       ("block 0x%lx (0x%lx<-->0x%lx) not owned by pysical list",
		(ulong) block, (ulong) block->pprev, (ulong )block->pnext));
    return 1;
  }

err1:
  //forward
  block = point;
  do
  {
    if (block->pnext->pprev != block)
    {
      DBUG_PRINT("error",
		 ("block 0x%lx in physicel list is incorrect linked, next block 0x%lx refered as prev to 0x%lx (check from 0x%lx)",
		  (ulong) block, (ulong) block->pnext,
		  (ulong) block->pnext->pprev,
		  (ulong) point));
      //back trace
      for (; block != point; block = block->pprev)
	    DBUG_PRINT("error", ("back trace 0x%lx", (ulong) block));
      result = 1;
      goto err2;
    }
    block = block->pnext;
  } while (block != first_block);
err2:
  return result;
}


my_bool Query_cache::in_list(Query_cache_block * root,
			     Query_cache_block * point,
			     const char *name)
{
  my_bool result = 0;
  Query_cache_block *block = point;
  //back
  do
  {
    if (block->prev->next != block)
    {
      DBUG_PRINT("error",
		 ("block 0x%lx in list '%s' 0x%lx is incorrect linked, prev block 0x%lx refered as next to 0x%lx (check from 0x%lx)",
		  (ulong) block, name, (ulong) root, (ulong) block->prev,
		  (ulong) block->prev->next,
		  (ulong) point));
      //back trace
      for (; block != point; block = block->next)
	    DBUG_PRINT("error", ("back trace 0x%lx", (ulong) block));
      result = 1;
      goto err1;
    }
    block = block->prev;
  } while (block != root && block != point);
  if (block != root)
  {
    DBUG_PRINT("error",
	       ("block 0x%lx (0x%lx<-->0x%lx) not owned by list '%s' 0x%lx",
		(ulong) block,
		(ulong) block->prev, (ulong) block->next,
		name, (ulong) root));
    return 1;
  }
err1:
  // forward
  block = point;
  do
  {
    if (block->next->prev != block)
    {
      DBUG_PRINT("error",
		 ("block 0x%lx in list '%s' 0x%lx is incorrect linked, next block 0x%lx refered as prev to 0x%lx (check from 0x%lx)",
		  (ulong) block, name, (ulong) root, (ulong) block->next,
		  (ulong) block->next->prev,
		  (ulong) point));
      //back trace
      for (; block != point; block = block->prev)
	    DBUG_PRINT("error", ("back trace 0x%lx", (ulong) block));
      result = 1;
      goto err2;
    }
    block = block->next;
  } while (block != root);
err2:
  return result;
}

void dump_node(Query_cache_block_table * node,
	       const char * call, const char * descr)
{
  DBUG_PRINT("qcache", ("%s: %s: node: 0x%lx", call, descr, (ulong) node));
  DBUG_PRINT("qcache", ("%s: %s: node block: 0x%lx",
			call, descr, (ulong) node->block()));
  DBUG_PRINT("qcache", ("%s: %s: next: 0x%lx", call, descr,
			(ulong) node->next));
  DBUG_PRINT("qcache", ("%s: %s: prev: 0x%lx", call, descr,
			(ulong) node->prev));
}

my_bool Query_cache::in_table_list(Query_cache_block_table * root,
				   Query_cache_block_table * point,
				   const char *name)
{
  my_bool result = 0;
  Query_cache_block_table *table = point;
  dump_node(root, name, "parameter root");
  //back
  do
  {
    dump_node(table, name, "list element << ");
    if (table->prev->next != table)
    {
      DBUG_PRINT("error",
		 ("table 0x%lx(0x%lx) in list '%s' 0x%lx(0x%lx) is incorrect linked, prev table 0x%lx(0x%lx) refered as next to 0x%lx(0x%lx) (check from 0x%lx(0x%lx))",
		  (ulong) table, (ulong) table->block(), name,
		  (ulong) root, (ulong) root->block(),
		  (ulong) table->prev, (ulong) table->prev->block(),
		  (ulong) table->prev->next,
		  (ulong) table->prev->next->block(),
		  (ulong) point, (ulong) point->block()));
      //back trace
      for (; table != point; table = table->next)
	    DBUG_PRINT("error", ("back trace 0x%lx(0x%lx)",
				 (ulong) table, (ulong) table->block()));
      result = 1;
      goto err1;
    }
    table = table->prev;
  } while (table != root && table != point);
  if (table != root)
  {
    DBUG_PRINT("error",
	       ("table 0x%lx(0x%lx) (0x%lx(0x%lx)<-->0x%lx(0x%lx)) not owned by list '%s' 0x%lx(0x%lx)",
		(ulong) table, (ulong) table->block(),
		(ulong) table->prev, (ulong) table->prev->block(),
		(ulong) table->next, (ulong) table->next->block(),
		name, (ulong) root, (ulong) root->block()));
    return 1;
  }
err1:
  // forward
  table = point;
  do
  {
    dump_node(table, name, "list element >> ");
    if (table->next->prev != table)
    {
      DBUG_PRINT("error",
		 ("table 0x%lx(0x%lx) in list '%s' 0x%lx(0x%lx) is incorrect linked, next table 0x%lx(0x%lx) refered as prev to 0x%lx(0x%lx) (check from 0x%lx(0x%lx))",
		  (ulong) table, (ulong) table->block(),
		  name, (ulong) root, (ulong) root->block(),
		  (ulong) table->next, (ulong) table->next->block(),
		  (ulong) table->next->prev,
		  (ulong) table->next->prev->block(),
		  (ulong) point, (ulong) point->block()));
      //back trace
      for (; table != point; table = table->prev)
	    DBUG_PRINT("error", ("back trace 0x%lx(0x%lx)",
				 (ulong) table, (ulong) table->block()));
      result = 1;
      goto err2;
    }
    table = table->next;
  } while (table != root);
err2:
  return result;
}

#endif /* NDEBUG */