storage/perfschema/table_session_variables.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_session_variables.cc
  Table SESSION_VARIABLES (implementation).
*/

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

THR_LOCK table_session_variables::m_table_lock;

static const TABLE_FIELD_TYPE field_types[]=
{
  {
    { 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_session_variables::m_field_def=
{ 2, field_types };

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

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

ha_rows table_session_variables::get_row_count(void)
{
  mysql_mutex_lock(&LOCK_plugin_delete);
  mysql_rwlock_rdlock(&LOCK_system_variables_hash);
  ha_rows system_var_count= get_system_variable_hash_records();
  mysql_rwlock_unlock(&LOCK_system_variables_hash);
  mysql_mutex_unlock(&LOCK_plugin_delete);
  return system_var_count;
}

table_session_variables::table_session_variables()
  : PFS_engine_table(&m_share, &m_pos),
    m_sysvar_cache(false), m_row_exists(false), m_pos(0), m_next_pos(0)
{}

void table_session_variables::reset_position(void)
{
  m_pos.m_index = 0;
  m_next_pos.m_index = 0;
}

int table_session_variables::rnd_init(bool scan)
{
  /* Build a cache of system variables for this thread. */
  m_sysvar_cache.materialize_all(current_thd);

  /* 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.
    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_session_variables_context *)current_thd->alloc(sizeof(table_session_variables_context));
  new(m_context) table_session_variables_context(hash_version, !scan);
  return 0;
}

int table_session_variables::rnd_next(void)
{
  for (m_pos.set_at(&m_next_pos);
       m_pos.m_index < m_sysvar_cache.size();
       m_pos.next())
  {
    if (m_sysvar_cache.is_materialized())
    {
      const System_variable *system_var= m_sysvar_cache.get(m_pos.m_index);
      if (system_var != NULL)
      {
        make_row(system_var);
        m_next_pos.set_after(&m_pos);
        return 0;
      }
    }
  }
  return HA_ERR_END_OF_FILE;
}

int table_session_variables::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 < m_sysvar_cache.size());

  if (m_sysvar_cache.is_materialized())
  {
    const System_variable *system_var= m_sysvar_cache.get(m_pos.m_index);
    if (system_var != NULL)
    {
      make_row(system_var);
      return 0;
    }
  }
  return HA_ERR_RECORD_DELETED;
}

void table_session_variables
::make_row(const System_variable *system_var)
{
  m_row_exists= false;
  if (system_var->is_null() || system_var->is_ignored())
    return;
  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);
  m_row_exists= true;
}

int table_session_variables
::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: /* VARIABLE_NAME */
        set_field_varchar_utf8(f, m_row.m_variable_name.m_str, m_row.m_variable_name.m_length);
        break;
      case 1: /* VARIABLE_VALUE */
        m_row.m_variable_value.set_field(f);
        break;
      default:
        assert(false);
      }
    }
  }

  return 0;
}