storage/perfschema/table_variables_by_thread.cc

/* Copyright (c) 2015, 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, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file storage/perfschema/table_variables_by_thread.cc
  Table VARIABLES_BY_THREAD (implementation).
*/

#include "my_global.h"
#include "table_variables_by_thread.h"
#include "my_thread.h"
#include "pfs_instr_class.h"
#include "pfs_column_types.h"
#include "pfs_column_values.h"
#include "pfs_global.h"

THR_LOCK table_variables_by_thread::m_table_lock;

static const TABLE_FIELD_TYPE field_types[]=
{
  {
    { C_STRING_WITH_LEN("THREAD_ID") },
    { C_STRING_WITH_LEN("bigint(20)") },
    { NULL, 0}
  },
  {
    { C_STRING_WITH_LEN("VARIABLE_NAME") },
    { C_STRING_WITH_LEN("varchar(64)") },
    { NULL, 0}
  },
  {
    { C_STRING_WITH_LEN("VARIABLE_VALUE") },
    { C_STRING_WITH_LEN("varchar(1024)") },
    { NULL, 0}
  }
};

TABLE_FIELD_DEF
table_variables_by_thread::m_field_def=
{ 3, field_types };

PFS_engine_table_share
table_variables_by_thread::m_share=
{
  { C_STRING_WITH_LEN("variables_by_thread") },
  &pfs_readonly_acl,
  table_variables_by_thread::create,
  NULL, /* write_row */
  NULL, /* delete_all_rows */
  table_variables_by_thread::get_row_count,
  sizeof(pos_t),
  &m_table_lock,
  &m_field_def,
  false, /* checked */
  true   /* perpetual */
};

PFS_engine_table*
table_variables_by_thread::create(void)
{
  return new table_variables_by_thread();
}

ha_rows table_variables_by_thread::get_row_count(void)
{
  mysql_mutex_lock(&LOCK_plugin_delete);
  mysql_rwlock_rdlock(&LOCK_system_variables_hash);
  ulong system_var_count= get_system_variable_hash_records();
  mysql_rwlock_unlock(&LOCK_system_variables_hash);
  mysql_mutex_unlock(&LOCK_plugin_delete);
  return (global_thread_container.get_row_count() * system_var_count);
}

table_variables_by_thread::table_variables_by_thread()
  : PFS_engine_table(&m_share, &m_pos),
    m_sysvar_cache(true), m_row_exists(false), m_pos(), m_next_pos(), m_context(NULL)
{}

void table_variables_by_thread::reset_position(void)
{
  m_pos.reset();
  m_next_pos.reset();
}

int table_variables_by_thread::rnd_init(bool scan)
{
  /*
    Build array of SHOW_VARs from system variable hash prior to materializing
    threads in rnd_next() or rnd_pos().
  */
  m_sysvar_cache.initialize_session();

  /* Record the version of the system variable hash. */
  ulonglong hash_version= m_sysvar_cache.get_sysvar_hash_version();

  /*
    The table context holds the current version of the system variable hash and
    a record of which threads were materialized.
    If scan == true, then allocate a new context from mem_root and store in TLS.
    If scan == false, then restore from TLS.
  */
  m_context= (table_variables_by_thread_context *)current_thd->alloc(sizeof(table_variables_by_thread_context));
  new(m_context) table_variables_by_thread_context(hash_version, !scan);
  return 0;
}

int table_variables_by_thread::rnd_next(void)
{
  /* If system variable hash changes, exit with warning. */ // TODO: Issue warning
  if (!m_context->versions_match())
    return HA_ERR_END_OF_FILE;

  bool has_more_thread= true;

  for (m_pos.set_at(&m_next_pos);
       has_more_thread;
       m_pos.next_thread())
  {
    PFS_thread *pfs_thread= global_thread_container.get(m_pos.m_index_1, &has_more_thread);

    /* Materialize all variables for the current thread. Assign a dedicated mem_root. */
    if (m_sysvar_cache.materialize_session(pfs_thread, true) == 0)
    {
      /* Mark this thread as materialized. */
      m_context->set_item(m_pos.m_index_1);

      const System_variable *system_var= m_sysvar_cache.get(m_pos.m_index_2);
      if (system_var != NULL)
      {
        make_row(pfs_thread, system_var);
        m_next_pos.set_after(&m_pos);
        return 0;
      }
    }
  }
  return HA_ERR_END_OF_FILE;
}

int
table_variables_by_thread::rnd_pos(const void *pos)
{
  /* If system variable hash changes, do nothing. */
  if (!m_context->versions_match())
    return HA_ERR_RECORD_DELETED;

  set_position(pos);
  assert(m_pos.m_index_1 < global_thread_container.get_row_count());

  PFS_thread *pfs_thread= global_thread_container.get(m_pos.m_index_1);
    /*
    Only materialize threads that were previously materialized by rnd_next().
    If a thread cannot be rematerialized, then do nothing.
    Only materialize the requested system variable to avoid repeated
    materialization of each thread, such as with ORDER BY variable_name.
  */
  if (m_context->is_item_set(m_pos.m_index_1) &&
      /* Materialize only the requested variable. */
      m_sysvar_cache.materialize_session(pfs_thread, m_pos.m_index_2) == 0)
  {
    /* Get the first (and only) element from the cache. */
    const System_variable *system_var= m_sysvar_cache.get();
    if (system_var != NULL)
    {
      make_row(pfs_thread, system_var);
      m_next_pos.set_after(&m_pos);
      return 0;
    }
  }
  return HA_ERR_RECORD_DELETED;
}

void table_variables_by_thread
::make_row(PFS_thread *thread, const System_variable *system_var)
{
  pfs_optimistic_state lock;
  m_row_exists= false;
  if (system_var->is_null() || system_var->is_ignored())
    return;

  /* Protect this reader against a thread termination */
  thread->m_lock.begin_optimistic_lock(&lock);

  m_row.m_thread_internal_id= thread->m_thread_internal_id;
  m_row.m_variable_name.make_row(system_var->m_name, system_var->m_name_length);
  m_row.m_variable_value.make_row(system_var);

  if (!thread->m_lock.end_optimistic_lock(&lock))
    return;

  m_row_exists= true;
}

int table_variables_by_thread
::read_row_values(TABLE *table,
                  unsigned char *buf,
                  Field **fields,
                  bool read_all)
{
  Field *f;

  if (unlikely(! m_row_exists))
    return HA_ERR_RECORD_DELETED;

  /* Set the null bits */
  assert(table->s->null_bytes == 1);
  buf[0]= 0;

  for (; (f= *fields) ; fields++)
  {
    if (read_all || bitmap_is_set(table->read_set, f->field_index))
    {
      switch(f->field_index)
      {
      case 0: /* THREAD_ID */
        set_field_ulonglong(f, m_row.m_thread_internal_id);
        break;
      case 1: /* VARIABLE_NAME */
        set_field_varchar_utf8(f, m_row.m_variable_name.m_str, m_row.m_variable_name.m_length);
        break;
      case 2: /* VARIABLE_VALUE */
        m_row.m_variable_value.set_field(f);
        break;
      default:
        assert(false);
      }
    }
  }

  return 0;
}