path: root/sql/sys_vars.cc

/* Copyright (c) 2002, 2015, Oracle and/or its affiliates.
   Copyright (c) 2012, 2015, MariaDB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   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 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 02110-1335  USA */

/*
  How to add new variables:

  1. copy one of the existing variables, and edit the declaration.
  2. if you need special behavior on assignment or additional checks
     use ON_CHECK and ON_UPDATE callbacks.
  3. *Don't* add new Sys_var classes or uncle Occam will come
     with his razor to haunt you at nights

  Note - all storage engine variables (for example myisam_whatever)
  should go into the corresponding storage engine sources
  (for example in storage/myisam/ha_myisam.cc) !
*/

#include "my_global.h"                          /* NO_EMBEDDED_ACCESS_CHECKS */
#include "sql_priv.h"
#include "sql_class.h"                          // set_var.h: THD
#include "sql_parse.h"
#include "sys_vars.h"

#include "events.h"
#include <thr_alarm.h>
#include "slave.h"
#include "rpl_mi.h"
#include "transaction.h"
#include "mysqld.h"
#include "lock.h"
#include "sql_time.h"                       // known_date_time_formats
#include "sql_acl.h" // SUPER_ACL,
                     // mysql_user_table_is_in_short_password_format
#include "derror.h"  // read_texts
#include "sql_base.h"                           // close_cached_tables
#include <myisam.h>
#include "log_slow.h"
#include "debug_sync.h"                         // DEBUG_SYNC
#include "sql_show.h"

#include "log_event.h"
#ifdef WITH_PERFSCHEMA_STORAGE_ENGINE
#include "../storage/perfschema/pfs_server.h"
#endif /* WITH_PERFSCHEMA_STORAGE_ENGINE */
#include "threadpool.h"

/*
  The rule for this file: everything should be 'static'. When a sys_var
  variable or a function from this file is - in very rare cases - needed
  elsewhere it should be explicitly declared 'export' here to show that it's
  not a mistakenly forgotten 'static' keyword.
*/
#define export /* not static */

#ifdef WITH_PERFSCHEMA_STORAGE_ENGINE

static Sys_var_mybool Sys_pfs_enabled(
       "performance_schema",
       "Enable the performance schema.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_ulong Sys_pfs_events_waits_history_long_size(
       "performance_schema_events_waits_history_long_size",
       "Number of rows in EVENTS_WAITS_HISTORY_LONG.",
       PARSED_EARLY READ_ONLY
       GLOBAL_VAR(pfs_param.m_events_waits_history_long_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_WAITS_HISTORY_LONG_SIZE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_events_waits_history_size(
       "performance_schema_events_waits_history_size",
       "Number of rows per thread in EVENTS_WAITS_HISTORY.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_events_waits_history_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024),
       DEFAULT(PFS_WAITS_HISTORY_SIZE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_cond_classes(
       "performance_schema_max_cond_classes",
       "Maximum number of condition instruments.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_cond_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_COND_CLASS), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_cond_instances(
       "performance_schema_max_cond_instances",
       "Maximum number of instrumented condition objects.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_cond_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_COND), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_file_classes(
       "performance_schema_max_file_classes",
       "Maximum number of file instruments.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_file_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_FILE_CLASS), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_file_handles(
       "performance_schema_max_file_handles",
       "Maximum number of opened instrumented files.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_file_handle_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_FILE_HANDLE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_file_instances(
       "performance_schema_max_file_instances",
       "Maximum number of instrumented files.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_file_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_FILE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_mutex_classes(
       "performance_schema_max_mutex_classes",
       "Maximum number of mutex instruments.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_mutex_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_MUTEX_CLASS), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_mutex_instances(
       "performance_schema_max_mutex_instances",
       "Maximum number of instrumented MUTEX objects.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_mutex_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 100*1024*1024),
       DEFAULT(PFS_MAX_MUTEX), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_rwlock_classes(
       "performance_schema_max_rwlock_classes",
       "Maximum number of rwlock instruments.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_rwlock_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_RWLOCK_CLASS), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_rwlock_instances(
       "performance_schema_max_rwlock_instances",
       "Maximum number of instrumented RWLOCK objects.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_rwlock_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 100*1024*1024),
       DEFAULT(PFS_MAX_RWLOCK), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_table_handles(
       "performance_schema_max_table_handles",
       "Maximum number of opened instrumented tables.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_table_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_TABLE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_table_instances(
       "performance_schema_max_table_instances",
       "Maximum number of instrumented tables.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_table_share_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_TABLE_SHARE), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_thread_classes(
       "performance_schema_max_thread_classes",
       "Maximum number of thread instruments.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_thread_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_THREAD_CLASS), BLOCK_SIZE(1));

static Sys_var_ulong Sys_pfs_max_thread_instances(
       "performance_schema_max_thread_instances",
       "Maximum number of instrumented threads.",
       PARSED_EARLY READ_ONLY GLOBAL_VAR(pfs_param.m_thread_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_THREAD), BLOCK_SIZE(1));

#endif /* WITH_PERFSCHEMA_STORAGE_ENGINE */

static Sys_var_ulong Sys_auto_increment_increment(
       "auto_increment_increment",
       "Auto-increment columns are incremented by this",
       SESSION_VAR(auto_increment_increment),
       CMD_LINE(OPT_ARG),
       VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_ulong Sys_auto_increment_offset(
       "auto_increment_offset",
       "Offset added to Auto-increment columns. Used when "
       "auto-increment-increment != 1",
       SESSION_VAR(auto_increment_offset),
       CMD_LINE(OPT_ARG),
       VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_mybool Sys_automatic_sp_privileges(
       "automatic_sp_privileges",
       "Creating and dropping stored procedures alters ACLs",
       GLOBAL_VAR(sp_automatic_privileges),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_ulong Sys_back_log(
       "back_log", "The number of outstanding connection requests "
       "MySQL can have. This comes into play when the main MySQL thread "
       "gets very many connection requests in a very short time",
       READ_ONLY GLOBAL_VAR(back_log), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 65535), DEFAULT(50), BLOCK_SIZE(1));

static Sys_var_charptr Sys_basedir(
       "basedir", "Path to installation directory. All paths are "
       "usually resolved relative to this",
       READ_ONLY GLOBAL_VAR(mysql_home_ptr), CMD_LINE(REQUIRED_ARG, 'b'),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_ulonglong Sys_binlog_cache_size(
       "binlog_cache_size", "The size of the transactional cache for "
       "updates to transactional engines for the binary log. "
       "If you often use transactions containing many statements, "
       "you can increase this to get more performance",
       GLOBAL_VAR(binlog_cache_size),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, SIZE_T_MAX), DEFAULT(32768), BLOCK_SIZE(IO_SIZE));

static Sys_var_ulonglong Sys_binlog_stmt_cache_size(
       "binlog_stmt_cache_size", "The size of the statement cache for "
       "updates to non-transactional engines for the binary log. "
       "If you often use statements updating a great number of rows, "
       "you can increase this to get more performance",
       GLOBAL_VAR(binlog_stmt_cache_size),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, SIZE_T_MAX), DEFAULT(32768), BLOCK_SIZE(IO_SIZE));

/*
  Some variables like @sql_log_bin and @binlog_format change how/if binlogging
  is done. We must not change them inside a running transaction or statement,
  otherwise the event group eventually written to the binlog may become
  incomplete or otherwise garbled.

  This function does the appropriate check.

  It returns true if an error is caused by incorrect usage, false if ok.
*/
static bool
error_if_in_trans_or_substatement(THD *thd, int in_substatement_error,
                                  int in_transaction_error)
{
  if (thd->in_sub_stmt)
  {
    my_error(in_substatement_error, MYF(0));
    return true;
  }

  if (thd->in_active_multi_stmt_transaction())
  {
    my_error(in_transaction_error, MYF(0));
    return true;
  }

  return false;
}

static bool check_has_super(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ASSERT(self->scope() != sys_var::GLOBAL);// don't abuse check_has_super()
#ifndef NO_EMBEDDED_ACCESS_CHECKS
  if (!(thd->security_ctx->master_access & SUPER_ACL))
  {
    my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "SUPER");
    return true;
  }
#endif
  return false;
}
static bool binlog_format_check(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return true;

  if (var->type == OPT_GLOBAL)
    return false;

  /*
     If RBR and open temporary tables, their CREATE TABLE may not be in the
     binlog, so we can't toggle to SBR in this connection.

     If binlog_format=MIXED, there are open temporary tables, and an unsafe
     statement is executed, then subsequent statements are logged in row
     format and hence changes to temporary tables may be lost. So we forbid
     switching @@SESSION.binlog_format from MIXED to STATEMENT when there are
     open temp tables and we are logging in row format.
  */
  if (thd->temporary_tables && var->type == OPT_SESSION &&
      var->save_result.ulonglong_value == BINLOG_FORMAT_STMT &&
      ((thd->variables.binlog_format == BINLOG_FORMAT_MIXED &&
        thd->is_current_stmt_binlog_format_row()) ||
       thd->variables.binlog_format == BINLOG_FORMAT_ROW))
  {
    my_error(ER_TEMP_TABLE_PREVENTS_SWITCH_OUT_OF_RBR, MYF(0));
    return true;
  }

  if (error_if_in_trans_or_substatement(thd,
         ER_STORED_FUNCTION_PREVENTS_SWITCH_BINLOG_FORMAT,
         ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_BINLOG_FORMAT))
    return true;

  return false;
}

static bool fix_binlog_format_after_update(sys_var *self, THD *thd,
                                           enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->reset_current_stmt_binlog_format_row();
  return false;
}

static Sys_var_enum Sys_binlog_format(
       "binlog_format", "What form of binary logging the master will "
       "use: either ROW for row-based binary logging, STATEMENT "
       "for statement-based binary logging, or MIXED. MIXED is statement-"
       "based binary logging except for those statements where only row-"
       "based is correct: those which involve user-defined functions (i.e. "
       "UDFs) or the UUID() function; for those, row-based binary logging is "
       "automatically used. If NDBCLUSTER is enabled and binlog-format is "
       "MIXED, the format switches to row-based and back implicitly per each "
       "query accessing an NDBCLUSTER table",
       SESSION_VAR(binlog_format), CMD_LINE(REQUIRED_ARG, OPT_BINLOG_FORMAT),
       binlog_format_names, DEFAULT(BINLOG_FORMAT_STMT),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(binlog_format_check),
       ON_UPDATE(fix_binlog_format_after_update));

static bool binlog_direct_check(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return true;

  if (var->type == OPT_GLOBAL)
    return false;

  if (error_if_in_trans_or_substatement(thd,
          ER_STORED_FUNCTION_PREVENTS_SWITCH_BINLOG_DIRECT,
          ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_BINLOG_DIRECT))
     return true;

  return false;
}

static Sys_var_mybool Sys_binlog_direct(
       "binlog_direct_non_transactional_updates",
       "Causes updates to non-transactional engines using statement format to "
       "be written directly to binary log. Before using this option make sure "
       "that there are no dependencies between transactional and "
       "non-transactional tables such as in the statement INSERT INTO t_myisam "
       "SELECT * FROM t_innodb; otherwise, slaves may diverge from the master.",
       SESSION_VAR(binlog_direct_non_trans_update),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(binlog_direct_check));

static Sys_var_ulonglong Sys_bulk_insert_buff_size(
       "bulk_insert_buffer_size", "Size of tree cache used in bulk "
       "insert optimisation. Note that this is a limit per thread!",
       SESSION_VAR(bulk_insert_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, SIZE_T_MAX), DEFAULT(8192*1024), BLOCK_SIZE(1));

static Sys_var_charptr Sys_character_sets_dir(
       "character_sets_dir", "Directory where character sets are",
       READ_ONLY GLOBAL_VAR(charsets_dir), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static bool check_not_null(sys_var *self, THD *thd, set_var *var)
{
  return var->value && var->value->is_null();
}
static bool check_charset(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == STRING_RESULT)
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res=var->value->val_str(&str)))
      var->save_result.ptr= NULL;
    else if (!(var->save_result.ptr= get_charset_by_csname(res->c_ptr(),
                                                           MY_CS_PRIMARY,
                                                           MYF(0))) &&
             !(var->save_result.ptr=get_old_charset_by_name(res->c_ptr())))
    {
      ErrConvString err(res);
      my_error(ER_UNKNOWN_CHARACTER_SET, MYF(0), err.ptr());
      return true;
    }
  }
  else // INT_RESULT
  {
    int csno= (int)var->value->val_int();
    if (!(var->save_result.ptr= get_charset(csno, MYF(0))))
    {
      my_error(ER_UNKNOWN_CHARACTER_SET, MYF(0), llstr(csno, buff));
      return true;
    }
  }
  return false;
}
static bool check_charset_not_null(sys_var *self, THD *thd, set_var *var)
{
  return check_charset(self, thd, var) || check_not_null(self, thd, var);
}
static Sys_var_struct Sys_character_set_system(
       "character_set_system", "The character set used by the server "
       "for storing identifiers",
       READ_ONLY GLOBAL_VAR(system_charset_info), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(0));

static Sys_var_struct Sys_character_set_server(
       "character_set_server", "The default character set",
       SESSION_VAR(collation_server), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_not_null));

static bool check_charset_db(sys_var *self, THD *thd, set_var *var)
{
  if (check_charset_not_null(self, thd, var))
    return true;
  if (!var->value) // = DEFAULT
    var->save_result.ptr= thd->db_charset;
  return false;
}
static Sys_var_struct Sys_character_set_database(
       "character_set_database",
       " The character set used by the default database",
       SESSION_VAR(collation_database), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_db));

static bool check_cs_client(sys_var *self, THD *thd, set_var *var)
{
  if (check_charset_not_null(self, thd, var))
    return true;

  // Currently, UCS-2 cannot be used as a client character set
  if (!is_supported_parser_charset((CHARSET_INFO *)(var->save_result.ptr)))
    return true;

  return false;
}
static bool fix_thd_charset(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->update_charset();
  return false;
}
static Sys_var_struct Sys_character_set_client(
       "character_set_client", "The character set for statements "
       "that arrive from the client",
       SESSION_VAR(character_set_client), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_cs_client),
       ON_UPDATE(fix_thd_charset));

static Sys_var_struct Sys_character_set_connection(
       "character_set_connection", "The character set used for "
       "literals that do not have a character set introducer and for "
       "number-to-string conversion",
       SESSION_VAR(collation_connection), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_not_null),
       ON_UPDATE(fix_thd_charset));

static Sys_var_struct Sys_character_set_results(
       "character_set_results", "The character set used for returning "
       "query results to the client",
       SESSION_VAR(character_set_results), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_charset));

static Sys_var_struct Sys_character_set_filesystem(
       "character_set_filesystem", "The filesystem character set",
       SESSION_VAR(character_set_filesystem), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&character_set_filesystem),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_charset_not_null),
       ON_UPDATE(fix_thd_charset));

static const char *completion_type_names[]= {"NO_CHAIN", "CHAIN", "RELEASE", 0};
static Sys_var_enum Sys_completion_type(
       "completion_type", "The transaction completion type, one of "
       "NO_CHAIN, CHAIN, RELEASE",
       SESSION_VAR(completion_type), CMD_LINE(REQUIRED_ARG),
       completion_type_names, DEFAULT(0));

static bool check_collation_not_null(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == STRING_RESULT)
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res= var->value->val_str(&str)))
      var->save_result.ptr= NULL;
    else if (!(var->save_result.ptr= get_charset_by_name(res->c_ptr(), MYF(0))))
    {
      ErrConvString err(res);
      my_error(ER_UNKNOWN_COLLATION, MYF(0), err.ptr());
      return true;
    }
  }
  else // INT_RESULT
  {
    int csno= (int)var->value->val_int();
    if (!(var->save_result.ptr= get_charset(csno, MYF(0))))
    {
      my_error(ER_UNKNOWN_COLLATION, MYF(0), llstr(csno, buff));
      return true;
    }
  }
  return check_not_null(self, thd, var);
}
static Sys_var_struct Sys_collation_connection(
       "collation_connection", "The collation of the connection "
       "character set",
       SESSION_VAR(collation_connection), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_not_null),
       ON_UPDATE(fix_thd_charset));

static bool check_collation_db(sys_var *self, THD *thd, set_var *var)
{
  if (check_collation_not_null(self, thd, var))
    return true;
  if (!var->value) // = DEFAULT
    var->save_result.ptr= thd->db_charset;
  return false;
}
static Sys_var_struct Sys_collation_database(
       "collation_database", "The collation of the database "
       "character set",
       SESSION_VAR(collation_database), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_db));

static Sys_var_struct Sys_collation_server(
       "collation_server", "The server default collation",
       SESSION_VAR(collation_server), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_not_null));

static const char *concurrent_insert_names[]= {"NEVER", "AUTO", "ALWAYS", 0};
static Sys_var_enum Sys_concurrent_insert(
       "concurrent_insert", "Use concurrent insert with MyISAM. Possible "
       "values are NEVER, AUTO, ALWAYS",
       GLOBAL_VAR(myisam_concurrent_insert), CMD_LINE(OPT_ARG),
       concurrent_insert_names, DEFAULT(1));

static Sys_var_ulong Sys_connect_timeout(
       "connect_timeout",
       "The number of seconds the mysqld server is waiting for a connect "
       "packet before responding with 'Bad handshake'",
       GLOBAL_VAR(connect_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(2, LONG_TIMEOUT), DEFAULT(CONNECT_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_charptr Sys_datadir(
       "datadir", "Path to the database root directory",
       READ_ONLY GLOBAL_VAR(mysql_real_data_home_ptr),
       CMD_LINE(REQUIRED_ARG, 'h'), IN_FS_CHARSET, DEFAULT(mysql_real_data_home));

#ifndef DBUG_OFF
static Sys_var_dbug Sys_dbug(
       "debug", "Built-in DBUG debugger", sys_var::SESSION,
       CMD_LINE(OPT_ARG, '#'), DEFAULT(""), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_has_super), ON_UPDATE(0),
       DEPRECATED("'@@debug_dbug'"));

static Sys_var_dbug Sys_debug_dbug(
       "debug_dbug", "Built-in DBUG debugger", sys_var::SESSION,
       CMD_LINE(OPT_ARG, '#'), DEFAULT(""), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_has_super));
#endif

/**
  @todo
    When updating myisam_delay_key_write, we should do a 'flush tables'
    of all MyISAM tables to ensure that they are reopen with the
    new attribute.
*/
export bool fix_delay_key_write(sys_var *self, THD *thd, enum_var_type type)
{
  switch (delay_key_write_options) {
  case DELAY_KEY_WRITE_NONE:
    myisam_delay_key_write=0;
    ha_open_options&= ~HA_OPEN_DELAY_KEY_WRITE;
    break;
  case DELAY_KEY_WRITE_ON:
    myisam_delay_key_write=1;
    ha_open_options&= ~HA_OPEN_DELAY_KEY_WRITE;
    break;
  case DELAY_KEY_WRITE_ALL:
    myisam_delay_key_write=1;
    ha_open_options|= HA_OPEN_DELAY_KEY_WRITE;
    break;
  }
#ifdef WITH_ARIA_STORAGE_ENGINE
  maria_delay_key_write= myisam_delay_key_write;
#endif
  return false;
}
static const char *delay_key_write_names[]= { "OFF", "ON", "ALL", NullS };
static Sys_var_enum Sys_delay_key_write(
       "delay_key_write", "Type of DELAY_KEY_WRITE",
       GLOBAL_VAR(delay_key_write_options), CMD_LINE(OPT_ARG),
       delay_key_write_names, DEFAULT(DELAY_KEY_WRITE_ON),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_delay_key_write));

static Sys_var_ulong Sys_delayed_insert_limit(
       "delayed_insert_limit",
       "After inserting delayed_insert_limit rows, the INSERT DELAYED "
       "handler will check if there are any SELECT statements pending. "
       "If so, it allows these to execute before continuing",
       GLOBAL_VAR(delayed_insert_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(DELAYED_LIMIT), BLOCK_SIZE(1));

static Sys_var_ulong Sys_delayed_insert_timeout(
       "delayed_insert_timeout",
       "How long a INSERT DELAYED thread should wait for INSERT statements "
       "before terminating",
       GLOBAL_VAR(delayed_insert_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(DELAYED_WAIT_TIMEOUT),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_delayed_queue_size(
       "delayed_queue_size",
       "What size queue (in rows) should be allocated for handling INSERT "
       "DELAYED. If the queue becomes full, any client that does INSERT "
       "DELAYED will wait until there is room in the queue again",
       GLOBAL_VAR(delayed_queue_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(DELAYED_QUEUE_SIZE), BLOCK_SIZE(1));

#ifdef HAVE_EVENT_SCHEDULER
static const char *event_scheduler_names[]= { "OFF", "ON", "DISABLED", NullS };
static bool event_scheduler_check(sys_var *self, THD *thd, set_var *var)
{
  /* DISABLED is only accepted on the command line */
  if (var->save_result.ulonglong_value == Events::EVENTS_DISABLED)
    return true;
  /*
    If the scheduler was disabled because there are no/bad
    system tables, produce a more meaningful error message
    than ER_OPTION_PREVENTS_STATEMENT
  */
  if (Events::check_if_system_tables_error())
    return true;
  if (Events::opt_event_scheduler == Events::EVENTS_DISABLED)
  {
    my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0),
             "--event-scheduler=DISABLED or --skip-grant-tables");
    return true;
  }
  return false;
}
static bool event_scheduler_update(sys_var *self, THD *thd, enum_var_type type)
{
  int err_no= 0;
  uint opt_event_scheduler_value= Events::opt_event_scheduler;
  mysql_mutex_unlock(&LOCK_global_system_variables);
  /*
    Events::start() is heavyweight. In particular it creates a new THD,
    which takes LOCK_global_system_variables internally.
    Thus we have to release it here.
    We need to re-take it before returning, though.

    Note that since we release LOCK_global_system_variables before calling
    start/stop, there is a possibility that the server variable
    can become out of sync with the real event scheduler state.

    This can happen with two concurrent statments if the first gets
    interrupted after start/stop but before retaking
    LOCK_global_system_variables. However, this problem should be quite
    rare and it's difficult to avoid it without opening up possibilities
    for deadlocks. See bug#51160.
  */
  bool ret= opt_event_scheduler_value == Events::EVENTS_ON
            ? Events::start(&err_no)
            : Events::stop();
  mysql_mutex_lock(&LOCK_global_system_variables);
  if (ret)
  {
    Events::opt_event_scheduler= Events::EVENTS_OFF;
    my_error(ER_EVENT_SET_VAR_ERROR, MYF(0), err_no);
  }
  return ret;
}

static Sys_var_enum Sys_event_scheduler(
       "event_scheduler", "Enable the event scheduler. Possible values are "
       "ON, OFF, and DISABLED (keep the event scheduler completely "
       "deactivated, it cannot be activated run-time)",
       GLOBAL_VAR(Events::opt_event_scheduler), CMD_LINE(OPT_ARG),
       event_scheduler_names, DEFAULT(Events::EVENTS_OFF),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(event_scheduler_check), ON_UPDATE(event_scheduler_update));
#endif

static Sys_var_ulong Sys_expire_logs_days(
       "expire_logs_days",
       "If non-zero, binary logs will be purged after expire_logs_days "
       "days; possible purges happen at startup and at binary log rotation",
       GLOBAL_VAR(expire_logs_days),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 99), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_mybool Sys_flush(
       "flush", "Flush MyISAM tables to disk between SQL commands",
       GLOBAL_VAR(myisam_flush),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_ulong Sys_flush_time(
       "flush_time",
       "A dedicated thread is created to flush all tables at the "
       "given interval",
       GLOBAL_VAR(flush_time),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, LONG_TIMEOUT),
       DEFAULT(0), BLOCK_SIZE(1));

static bool check_ftb_syntax(sys_var *self, THD *thd, set_var *var)
{
  return ft_boolean_check_syntax_string((uchar*)
                      (var->save_result.string_value.str));
}
static bool query_cache_flush(sys_var *self, THD *thd, enum_var_type type)
{
#ifdef HAVE_QUERY_CACHE
  query_cache.flush();
#endif /* HAVE_QUERY_CACHE */
  return false;
}
/// @todo make SESSION_VAR (usability enhancement and a fix for a race condition)
static Sys_var_charptr Sys_ft_boolean_syntax(
       "ft_boolean_syntax", "List of operators for "
       "MATCH ... AGAINST ( ... IN BOOLEAN MODE)",
       GLOBAL_VAR(ft_boolean_syntax),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(DEFAULT_FTB_SYNTAX), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_ftb_syntax), ON_UPDATE(query_cache_flush));

static Sys_var_ulong Sys_ft_max_word_len(
       "ft_max_word_len",
       "The maximum length of the word to be included in a FULLTEXT index. "
       "Note: FULLTEXT indexes must be rebuilt after changing this variable",
       READ_ONLY GLOBAL_VAR(ft_max_word_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(10, HA_FT_MAXCHARLEN), DEFAULT(HA_FT_MAXCHARLEN),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_ft_min_word_len(
       "ft_min_word_len",
       "The minimum length of the word to be included in a FULLTEXT index. "
       "Note: FULLTEXT indexes must be rebuilt after changing this variable",
       READ_ONLY GLOBAL_VAR(ft_min_word_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, HA_FT_MAXCHARLEN), DEFAULT(4), BLOCK_SIZE(1));

/// @todo make it an updatable SESSION_VAR
static Sys_var_ulong Sys_ft_query_expansion_limit(
       "ft_query_expansion_limit",
       "Number of best matches to use for query expansion",
       READ_ONLY GLOBAL_VAR(ft_query_expansion_limit),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1000), DEFAULT(20), BLOCK_SIZE(1));

static Sys_var_charptr Sys_ft_stopword_file(
       "ft_stopword_file",
       "Use stopwords from this file instead of built-in list",
       READ_ONLY GLOBAL_VAR(ft_stopword_file), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_ignore_builtin_innodb(
       "ignore_builtin_innodb",
       "Disable initialization of builtin InnoDB plugin",
       READ_ONLY GLOBAL_VAR(opt_ignore_builtin_innodb),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static bool check_init_string(sys_var *self, THD *thd, set_var *var)
{
  if (var->save_result.string_value.str == 0)
  {
    var->save_result.string_value.str= const_cast<char*>("");
    var->save_result.string_value.length= 0;
  }
  return false;
}
static PolyLock_rwlock PLock_sys_init_connect(&LOCK_sys_init_connect);
static Sys_var_lexstring Sys_init_connect(
       "init_connect", "Command(s) that are executed for each "
       "new connection (unless the user has SUPER privilege)",
       GLOBAL_VAR(opt_init_connect), CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(""), &PLock_sys_init_connect, NOT_IN_BINLOG,
       ON_CHECK(check_init_string));

static Sys_var_charptr Sys_init_file(
       "init_file", "Read SQL commands from this file at startup",
       READ_ONLY GLOBAL_VAR(opt_init_file),
#ifdef DISABLE_GRANT_OPTIONS
       NO_CMD_LINE,
#else
       CMD_LINE(REQUIRED_ARG),
#endif
       IN_FS_CHARSET, DEFAULT(0));

static PolyLock_rwlock PLock_sys_init_slave(&LOCK_sys_init_slave);
static Sys_var_lexstring Sys_init_slave(
       "init_slave", "Command(s) that are executed by a slave server "
       "each time the SQL thread starts", GLOBAL_VAR(opt_init_slave),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(""), &PLock_sys_init_slave,
       NOT_IN_BINLOG, ON_CHECK(check_init_string));

static Sys_var_ulong Sys_interactive_timeout(
       "interactive_timeout",
       "The number of seconds the server waits for activity on an interactive "
       "connection before closing it",
       SESSION_VAR(net_interactive_timeout),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_WAIT_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_join_buffer_size(
       "join_buffer_size",
       "The size of the buffer that is used for joins",
       SESSION_VAR(join_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(128, SIZE_T_MAX), DEFAULT(128*1024), BLOCK_SIZE(128));

static Sys_var_keycache Sys_key_buffer_size(
       "key_buffer_size", "The size of the buffer used for "
       "index blocks for MyISAM tables. Increase this to get better index "
       "handling (for all reads and multiple writes) to as much as you can "
       "afford",
       KEYCACHE_VAR(param_buff_size),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_BUFFER_SIZE),
       VALID_RANGE(0, SIZE_T_MAX), DEFAULT(KEY_CACHE_SIZE),
       BLOCK_SIZE(IO_SIZE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_buffer_size));

static Sys_var_keycache Sys_key_cache_block_size(
       "key_cache_block_size", "The default size of key cache blocks",
       KEYCACHE_VAR(param_block_size),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_BLOCK_SIZE),
       VALID_RANGE(512, 1024*16), DEFAULT(KEY_CACHE_BLOCK_SIZE),
       BLOCK_SIZE(512), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(resize_keycache));

static Sys_var_keycache Sys_key_cache_division_limit(
       "key_cache_division_limit",
       "The minimum percentage of warm blocks in key cache",
       KEYCACHE_VAR(param_division_limit),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_DIVISION_LIMIT),
       VALID_RANGE(1, 100), DEFAULT(100),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(change_keycache_param));

static Sys_var_keycache Sys_key_cache_age_threshold(
       "key_cache_age_threshold", "This characterizes the number of "
       "hits a hot block has to be untouched until it is considered aged "
       "enough to be downgraded to a warm block. This specifies the "
       "percentage ratio of that number of hits to the total number of "
       "blocks in key cache",
       KEYCACHE_VAR(param_age_threshold),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_AGE_THRESHOLD),
       VALID_RANGE(100, UINT_MAX), DEFAULT(300),
       BLOCK_SIZE(100), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(change_keycache_param));

static Sys_var_mybool Sys_large_files_support(
       "large_files_support",
       "Whether mysqld was compiled with options for large file support",
       READ_ONLY GLOBAL_VAR(opt_large_files),
       NO_CMD_LINE, DEFAULT(sizeof(my_off_t) > 4));

static Sys_var_uint Sys_large_page_size(
       "large_page_size",
       "If large page support is enabled, this shows the size of memory pages",
       READ_ONLY GLOBAL_VAR(opt_large_page_size), NO_CMD_LINE,
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_mybool Sys_large_pages(
       "large_pages", "Enable support for large pages",
       READ_ONLY GLOBAL_VAR(opt_large_pages),
       IF_WIN(NO_CMD_LINE, CMD_LINE(OPT_ARG)), DEFAULT(FALSE));

static Sys_var_charptr Sys_language(
       "lc_messages_dir", "Directory where error messages are",
       READ_ONLY GLOBAL_VAR(lc_messages_dir_ptr), CMD_LINE(REQUIRED_ARG, 'L'),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_local_infile(
       "local_infile", "Enable LOAD DATA LOCAL INFILE",
       GLOBAL_VAR(opt_local_infile), CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_ulong Sys_lock_wait_timeout(
       "lock_wait_timeout",
       "Timeout in seconds to wait for a lock before returning an error.",
       SESSION_VAR(lock_wait_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(LONG_TIMEOUT), BLOCK_SIZE(1));

#ifdef HAVE_MLOCKALL
static Sys_var_mybool Sys_locked_in_memory(
       "locked_in_memory",
       "Whether mysqld was locked in memory with --memlock",
       READ_ONLY GLOBAL_VAR(locked_in_memory), NO_CMD_LINE, DEFAULT(FALSE));
#endif

/* this says NO_CMD_LINE, as command-line option takes a string, not a bool */
static Sys_var_mybool Sys_log_bin(
       "log_bin", "Whether the binary log is enabled",
       READ_ONLY GLOBAL_VAR(opt_bin_log), NO_CMD_LINE, DEFAULT(FALSE));

static Sys_var_mybool Sys_trust_function_creators(
       "log_bin_trust_function_creators",
       "If set to FALSE (the default), then when --log-bin is used, creation "
       "of a stored function (or trigger) is allowed only to users having the "
       "SUPER privilege and only if this stored function (trigger) may not "
       "break binary logging. Note that if ALL connections to this server "
       "ALWAYS use row-based binary logging, the security issues do not "
       "exist and the binary logging cannot break, so you can safely set "
       "this to TRUE",
       GLOBAL_VAR(trust_function_creators),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_charptr Sys_log_error(
       "log_error",
       "Log errors to file (instead of stdout).  If file name is not specified "
       "then 'datadir'/'log-basename'.err or the 'pid-file' path with extension "
       ".err is used",
       READ_ONLY GLOBAL_VAR(log_error_file_ptr),
       CMD_LINE(OPT_ARG, OPT_LOG_ERROR),
       IN_FS_CHARSET, DEFAULT(disabled_my_option));

static Sys_var_mybool Sys_log_queries_not_using_indexes(
       "log_queries_not_using_indexes",
       "Log queries that are executed without benefit of any index to the "
       "slow log if it is open",
       GLOBAL_VAR(opt_log_queries_not_using_indexes),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_ulong Sys_log_warnings(
       "log_warnings",
       "Log some not critical warnings to the general log file."
       "Value can be between 0 and 11. Higher values mean more verbosity",
       SESSION_VAR(log_warnings),
       CMD_LINE(OPT_ARG, 'W'),
       VALID_RANGE(0, UINT_MAX), DEFAULT(1), BLOCK_SIZE(1));

static bool update_cached_long_query_time(sys_var *self, THD *thd,
                                          enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->variables.long_query_time=
      double2ulonglong(thd->variables.long_query_time_double * 1e6);
  else
    global_system_variables.long_query_time=
      double2ulonglong(global_system_variables.long_query_time_double * 1e6);
  return false;
}

static Sys_var_double Sys_long_query_time(
       "long_query_time",
       "Log all queries that have taken more than long_query_time seconds "
       "to execute to file. The argument will be treated as a decimal value "
       "with microsecond precision",
       SESSION_VAR(long_query_time_double),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, LONG_TIMEOUT), DEFAULT(10),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_cached_long_query_time));

static bool fix_low_prio_updates(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->update_lock_default= (thd->variables.low_priority_updates ?
                               TL_WRITE_LOW_PRIORITY : TL_WRITE);
  else
    thr_upgraded_concurrent_insert_lock=
      (global_system_variables.low_priority_updates ?
       TL_WRITE_LOW_PRIORITY : TL_WRITE);
  return false;
}
static Sys_var_mybool Sys_low_priority_updates(
       "low_priority_updates",
       "INSERT/DELETE/UPDATE has lower priority than selects",
       SESSION_VAR(low_priority_updates),
       CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_low_prio_updates));

#ifndef TO_BE_DELETED   /* Alias for the low_priority_updates */
static Sys_var_mybool Sys_sql_low_priority_updates(
       "sql_low_priority_updates",
       "INSERT/DELETE/UPDATE has lower priority than selects",
       SESSION_VAR(low_priority_updates), NO_CMD_LINE,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_low_prio_updates));
#endif

static Sys_var_mybool Sys_lower_case_file_system(
       "lower_case_file_system",
       "Case sensitivity of file names on the file system where the "
       "data directory is located",
       READ_ONLY GLOBAL_VAR(lower_case_file_system), NO_CMD_LINE,
       DEFAULT(FALSE));

static Sys_var_uint Sys_lower_case_table_names(
       "lower_case_table_names",
       "If set to 1 table names are stored in lowercase on disk and table "
       "names will be case-insensitive.  Should be set to 2 if you are using "
       "a case insensitive file system",
       READ_ONLY GLOBAL_VAR(lower_case_table_names),
       CMD_LINE(OPT_ARG, OPT_LOWER_CASE_TABLE_NAMES),
       VALID_RANGE(0, 2),
#ifdef FN_NO_CASE_SENSE
    DEFAULT(1),
#else
    DEFAULT(0),
#endif
       BLOCK_SIZE(1));

static bool session_readonly(sys_var *self, THD *thd, set_var *var)
{
  if (var->type == OPT_GLOBAL)
    return false;
  my_error(ER_VARIABLE_IS_READONLY, MYF(0), "SESSION",
           self->name.str, "GLOBAL");
  return true;
}

static bool check_max_allowed_packet(sys_var *self, THD *thd,  set_var *var)
{
  longlong val;
  if (session_readonly(self, thd, var))
    return true;

  val= var->save_result.ulonglong_value;
  if (val < (longlong) global_system_variables.net_buffer_length)
  {
    push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                        WARN_OPTION_BELOW_LIMIT, ER(WARN_OPTION_BELOW_LIMIT),
                        "max_allowed_packet", "net_buffer_length");
  }
  return false;
}


static Sys_var_ulong Sys_max_allowed_packet(
       "max_allowed_packet",
       "Max packet length to send to or receive from the server",
       SESSION_VAR(max_allowed_packet), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024*1024*1024), DEFAULT(1024*1024),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_allowed_packet));

static Sys_var_ulong Sys_slave_max_allowed_packet(
       "slave_max_allowed_packet",
       "The maximum packet length to sent successfully from the master to slave.",
       GLOBAL_VAR(slave_max_allowed_packet), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, MAX_MAX_ALLOWED_PACKET),
       DEFAULT(MAX_MAX_ALLOWED_PACKET),
       BLOCK_SIZE(1024));

static Sys_var_ulonglong Sys_max_binlog_cache_size(
       "max_binlog_cache_size",
       "Sets the total size of the transactional cache",
       GLOBAL_VAR(max_binlog_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, SIZE_T_MAX),
       DEFAULT((SIZE_T_MAX/IO_SIZE)*IO_SIZE),
       BLOCK_SIZE(IO_SIZE));

static Sys_var_ulonglong Sys_max_binlog_stmt_cache_size(
       "max_binlog_stmt_cache_size",
       "Sets the total size of the statement cache",
       GLOBAL_VAR(max_binlog_stmt_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, SIZE_T_MAX),
       DEFAULT((SIZE_T_MAX/IO_SIZE)*IO_SIZE),
       BLOCK_SIZE(IO_SIZE));

static bool fix_max_binlog_size(sys_var *self, THD *thd, enum_var_type type)
{
  mysql_bin_log.set_max_size(max_binlog_size);
#ifdef HAVE_REPLICATION
  if (!max_relay_log_size)
    active_mi->rli.relay_log.set_max_size(max_binlog_size);
#endif
  return false;
}
static Sys_var_ulong Sys_max_binlog_size(
       "max_binlog_size",
       "Binary log will be rotated automatically when the size exceeds this "
       "value. Will also apply to relay logs if max_relay_log_size is 0",
       GLOBAL_VAR(max_binlog_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, 1024*1024L*1024L), DEFAULT(1024*1024L*1024L),
       BLOCK_SIZE(IO_SIZE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_binlog_size));

static bool fix_max_connections(sys_var *self, THD *thd, enum_var_type type)
{
#ifndef EMBEDDED_LIBRARY
  resize_thr_alarm(max_connections + extra_max_connections +
                   global_system_variables.max_insert_delayed_threads + 10);
#endif
  return false;
}

// Default max_connections of 151 is larger than Apache's default max
// children, to avoid "too many connections" error in a common setup
static Sys_var_ulong Sys_max_connections(
       "max_connections", "The number of simultaneous clients allowed",
       GLOBAL_VAR(max_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 100000), DEFAULT(151), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_max_connections));

static Sys_var_ulong Sys_max_connect_errors(
       "max_connect_errors",
       "If there is more than this number of interrupted connections from "
       "a host this host will be blocked from further connections",
       GLOBAL_VAR(max_connect_errors), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(MAX_CONNECT_ERRORS),
       BLOCK_SIZE(1));

static bool check_max_delayed_threads(sys_var *self, THD *thd, set_var *var)
{
  return var->type != OPT_GLOBAL &&
         var->save_result.ulonglong_value != 0 &&
         var->save_result.ulonglong_value !=
                           global_system_variables.max_insert_delayed_threads;
}

// Alias for max_delayed_threads
static Sys_var_ulong Sys_max_insert_delayed_threads(
       "max_insert_delayed_threads",
       "Don't start more than this number of threads to handle INSERT "
       "DELAYED statements. If set to zero INSERT DELAYED will be not used",
       SESSION_VAR(max_insert_delayed_threads),
       NO_CMD_LINE, VALID_RANGE(0, 16384), DEFAULT(20),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_delayed_threads), ON_UPDATE(fix_max_connections));

static Sys_var_ulong Sys_max_delayed_threads(
       "max_delayed_threads",
       "Don't start more than this number of threads to handle INSERT "
       "DELAYED statements. If set to zero INSERT DELAYED will be not used",
       SESSION_VAR(max_insert_delayed_threads),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 16384), DEFAULT(20),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_delayed_threads), ON_UPDATE(fix_max_connections));

static Sys_var_ulong Sys_max_error_count(
       "max_error_count",
       "Max number of errors/warnings to store for a statement",
       SESSION_VAR(max_error_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 65535), DEFAULT(DEFAULT_ERROR_COUNT), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_max_heap_table_size(
       "max_heap_table_size",
       "Don't allow creation of heap tables bigger than this",
       SESSION_VAR(max_heap_table_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(16384, (ulonglong)~(intptr)0), DEFAULT(16*1024*1024),
       BLOCK_SIZE(1024));

static Sys_var_ulong Sys_metadata_locks_cache_size(
       "metadata_locks_cache_size", "Size of unused metadata locks cache",
       READ_ONLY GLOBAL_VAR(mdl_locks_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 1024*1024), DEFAULT(MDL_LOCKS_CACHE_SIZE_DEFAULT),
       BLOCK_SIZE(1));

/*
  "pseudo_thread_id" variable used in the test suite to detect 32/64bit
  systems.  If you change it to something else then ulong then fix the tests
  in mysql-test/include/have_32bit.inc and have_64bit.inc.
*/
static Sys_var_ulong Sys_pseudo_thread_id(
       "pseudo_thread_id",
       "This variable is for internal server use",
       SESSION_ONLY(pseudo_thread_id),
       NO_CMD_LINE, VALID_RANGE(0, ULONG_MAX), DEFAULT(0),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, IN_BINLOG,
       ON_CHECK(check_has_super));

static bool fix_max_join_size(sys_var *self, THD *thd, enum_var_type type)
{
  SV *sv= type == OPT_GLOBAL ? &global_system_variables : &thd->variables;
  if (sv->max_join_size == HA_POS_ERROR)
    sv->option_bits|= OPTION_BIG_SELECTS;
  else
    sv->option_bits&= ~OPTION_BIG_SELECTS;
  return false;
}
static Sys_var_harows Sys_max_join_size(
       "max_join_size",
       "Joins that are probably going to read more than max_join_size "
       "records return an error",
       SESSION_VAR(max_join_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, HA_POS_ERROR), DEFAULT(HA_POS_ERROR), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_join_size));

static Sys_var_ulong Sys_max_seeks_for_key(
       "max_seeks_for_key",
       "Limit assumed max number of seeks when looking up rows based on a key",
       SESSION_VAR(max_seeks_for_key), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(UINT_MAX), BLOCK_SIZE(1));

static Sys_var_ulong Sys_max_length_for_sort_data(
       "max_length_for_sort_data",
       "Max number of bytes in sorted records",
       SESSION_VAR(max_length_for_sort_data), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, 8192*1024L), DEFAULT(1024), BLOCK_SIZE(1));

static Sys_var_harows Sys_sql_max_join_size(
       "sql_max_join_size", "Alias for max_join_size",
       SESSION_VAR(max_join_size), NO_CMD_LINE,
       VALID_RANGE(1, HA_POS_ERROR), DEFAULT(HA_POS_ERROR), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_join_size), DEPRECATED("'@@max_join_size'"));

static Sys_var_ulong Sys_max_long_data_size(
       "max_long_data_size",
       "The maximum BLOB length to send to server from "
       "mysql_send_long_data API. Deprecated option; "
       "use max_allowed_packet instead.",
       READ_ONLY GLOBAL_VAR(max_long_data_size),
       CMD_LINE(REQUIRED_ARG, OPT_MAX_LONG_DATA_SIZE),
       VALID_RANGE(1024, UINT_MAX32), DEFAULT(1024*1024),
       BLOCK_SIZE(1));

static PolyLock_mutex PLock_prepared_stmt_count(&LOCK_prepared_stmt_count);
static Sys_var_ulong Sys_max_prepared_stmt_count(
       "max_prepared_stmt_count",
       "Maximum number of prepared statements in the server",
       GLOBAL_VAR(max_prepared_stmt_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1024*1024), DEFAULT(16382), BLOCK_SIZE(1),
       &PLock_prepared_stmt_count);

static bool fix_max_relay_log_size(sys_var *self, THD *thd, enum_var_type type)
{
#ifdef HAVE_REPLICATION
  active_mi->rli.relay_log.set_max_size(max_relay_log_size ?
                                        max_relay_log_size: max_binlog_size);
#endif
  return false;
}
static Sys_var_ulong Sys_max_relay_log_size(
       "max_relay_log_size",
       "If non-zero: relay log will be rotated automatically when the "
       "size exceeds this value; if zero: when the size "
       "exceeds max_binlog_size",
       GLOBAL_VAR(max_relay_log_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1024L*1024*1024), DEFAULT(0), BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_relay_log_size));

static Sys_var_ulong Sys_max_sort_length(
       "max_sort_length",
       "The number of bytes to use when sorting BLOB or TEXT values (only "
       "the first max_sort_length bytes of each value are used; the rest "
       "are ignored)",
       SESSION_VAR(max_sort_length), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, 8192*1024L), DEFAULT(1024), BLOCK_SIZE(1));

static Sys_var_ulong Sys_max_sp_recursion_depth(
       "max_sp_recursion_depth",
       "Maximum stored procedure recursion depth",
       SESSION_VAR(max_sp_recursion_depth), CMD_LINE(OPT_ARG),
       VALID_RANGE(0, 255), DEFAULT(0), BLOCK_SIZE(1));


static bool if_checking_enabled(sys_var *self, THD *thd,  set_var *var)
{
  if (session_readonly(self, thd, var))
    return true;
  
  if (!max_user_connections_checking)
  {
    my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--max-user-connections=0");
    return true;
  }

  return false;
}
// non-standard session_value_ptr() here
static Sys_var_max_user_conn Sys_max_user_connections(
       "max_user_connections",
       "The maximum number of active connections for a single user "
       "(0 = no limit)",
       SESSION_VAR(max_user_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(-1, INT_MAX), DEFAULT(0), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(if_checking_enabled));

static Sys_var_ulong Sys_max_tmp_tables(
       "max_tmp_tables",
       "Maximum number of temporary tables a client can keep open at a time",
       SESSION_VAR(max_tmp_tables), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(32), BLOCK_SIZE(1));

static Sys_var_ulong Sys_max_write_lock_count(
       "max_write_lock_count",
       "After this many write locks, allow some read locks to run in between",
       GLOBAL_VAR(max_write_lock_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(UINT_MAX), BLOCK_SIZE(1));

static Sys_var_ulong Sys_min_examined_row_limit(
       "min_examined_row_limit",
       "Don't write queries to slow log that examine fewer rows "
       "than that",
       SESSION_VAR(min_examined_row_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

#ifdef _WIN32
static Sys_var_mybool Sys_named_pipe(
       "named_pipe", "Enable the named pipe (NT)",
       READ_ONLY GLOBAL_VAR(opt_enable_named_pipe), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));
#endif


static bool check_net_buffer_length(sys_var *self, THD *thd,  set_var *var)
{
  longlong val;
  if (session_readonly(self, thd, var))
    return true;

  val= var->save_result.ulonglong_value;
  if (val > (longlong) global_system_variables.max_allowed_packet)
  {
    push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                        WARN_OPTION_BELOW_LIMIT, ER(WARN_OPTION_BELOW_LIMIT),
                        "max_allowed_packet", "net_buffer_length");
  }
  return false;
}
static Sys_var_ulong Sys_net_buffer_length(
       "net_buffer_length",
       "Buffer length for TCP/IP and socket communication",
       SESSION_VAR(net_buffer_length), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024*1024), DEFAULT(16384), BLOCK_SIZE(1024),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_net_buffer_length));

static bool fix_net_read_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    my_net_set_read_timeout(&thd->net, thd->variables.net_read_timeout);
  return false;
}
static Sys_var_ulong Sys_net_read_timeout(
       "net_read_timeout",
       "Number of seconds to wait for more data from a connection before "
       "aborting the read",
       SESSION_VAR(net_read_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_READ_TIMEOUT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_read_timeout));

static bool fix_net_write_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    my_net_set_write_timeout(&thd->net, thd->variables.net_write_timeout);
  return false;
}
static Sys_var_ulong Sys_net_write_timeout(
       "net_write_timeout",
       "Number of seconds to wait for a block to be written to a connection "
       "before aborting the write",
       SESSION_VAR(net_write_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_WRITE_TIMEOUT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_write_timeout));

static bool fix_net_retry_count(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    thd->net.retry_count=thd->variables.net_retry_count;
  return false;
}
static Sys_var_ulong Sys_net_retry_count(
       "net_retry_count",
       "If a read on a communication port is interrupted, retry this "
       "many times before giving up",
       SESSION_VAR(net_retry_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(MYSQLD_NET_RETRY_COUNT),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_retry_count));

static Sys_var_mybool Sys_old_mode(
       "old", "Use compatible behavior from previous MariaDB version. See also --old-mode",
       SESSION_VAR(old_mode), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_old_alter_table(
       "old_alter_table", "Use old, non-optimized alter table",
       SESSION_VAR(old_alter_table), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static bool check_old_passwords(sys_var *self, THD *thd, set_var *var)
{
  return mysql_user_table_is_in_short_password_format;
}
static Sys_var_mybool Sys_old_passwords(
       "old_passwords",
       "Use old password encryption method (needed for 4.0 and older clients)",
       SESSION_VAR(old_passwords), CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_old_passwords));

static Sys_var_ulong Sys_open_files_limit(
       "open_files_limit",
       "If this is not 0, then mysqld will use this value to reserve file "
       "descriptors to use with setrlimit(). If this value is 0 then mysqld "
       "will reserve max_connections*5 or max_connections + table_cache*2 "
       "(whichever is larger) number of file descriptors",
       READ_ONLY GLOBAL_VAR(open_files_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, OS_FILE_LIMIT), DEFAULT(0), BLOCK_SIZE(1));

/// @todo change to enum
static Sys_var_ulong Sys_optimizer_prune_level(
       "optimizer_prune_level",
       "Controls the heuristic(s) applied during query optimization to prune "
       "less-promising partial plans from the optimizer search space. "
       "Meaning: 0 - do not apply any heuristic, thus perform exhaustive "
       "search; 1 - prune plans based on number of retrieved rows",
       SESSION_VAR(optimizer_prune_level), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1), DEFAULT(1), BLOCK_SIZE(1));

/** Warns about deprecated value 63 */
static bool fix_optimizer_search_depth(sys_var *self, THD *thd,
                                       enum_var_type type)
{
  SV *sv= type == OPT_GLOBAL ? &global_system_variables : &thd->variables;
  if (sv->optimizer_search_depth == MAX_TABLES+2)
    WARN_DEPRECATED(thd, 6, 0, "optimizer-search-depth=63",
                    "a search depth less than 63");
  return false;
}

static Sys_var_ulong Sys_optimizer_search_depth(
       "optimizer_search_depth",
       "Maximum depth of search performed by the query optimizer. Values "
       "larger than the number of relations in a query result in better "
       "query plans, but take longer to compile a query. Values smaller "
       "than the number of tables in a relation result in faster "
       "optimization, but may produce very bad query plans. If set to 0, "
       "the system will automatically pick a reasonable value; if set to "
       "63, the optimizer will switch to the original find_best search. "
       "NOTE: The value 63 and its associated behaviour is deprecated",
       SESSION_VAR(optimizer_search_depth), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, MAX_TABLES+2), DEFAULT(MAX_TABLES+1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_optimizer_search_depth));

/* this is used in the sigsegv handler */
export const char *optimizer_switch_names[]=
{
  "index_merge","index_merge_union","index_merge_sort_union",
  "index_merge_intersection","index_merge_sort_intersection",
  "engine_condition_pushdown",
  "index_condition_pushdown",
  "derived_merge", "derived_with_keys",
  "firstmatch","loosescan","materialization","in_to_exists","semijoin",
  "partial_match_rowid_merge",
  "partial_match_table_scan",
  "subquery_cache",
  "mrr",
  "mrr_cost_based",
  "mrr_sort_keys",
  "outer_join_with_cache",
  "semijoin_with_cache",
  "join_cache_incremental",
  "join_cache_hashed",
  "join_cache_bka",
  "optimize_join_buffer_size",
  "table_elimination",
  "extended_keys",
  "default", NullS
};
/** propagates changes to @@engine_condition_pushdown */
static bool fix_optimizer_switch(sys_var *self, THD *thd,
                                 enum_var_type type)
{
  SV *sv= (type == OPT_GLOBAL) ? &global_system_variables : &thd->variables;
  sv->engine_condition_pushdown=
    test(sv->optimizer_switch & OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN);
  return false;
}
static Sys_var_flagset Sys_optimizer_switch(
       "optimizer_switch",
       "optimizer_switch=option=val[,option=val...], where option is one of {"
        "derived_merge, "
        "derived_with_keys, "
        "firstmatch, "
        "in_to_exists, "
        "engine_condition_pushdown, "
        "index_condition_pushdown, "
        "index_merge, "
        "index_merge_intersection, "
        "index_merge_sort_intersection, "
        "index_merge_sort_union, "
        "index_merge_union, "
        "join_cache_bka, "
        "join_cache_hashed, "
        "join_cache_incremental, "
        "loosescan, "
        "materialization, "
        "mrr, "
        "mrr_cost_based, "
        "mrr_sort_keys, "
        "optimize_join_buffer_size, "
        "outer_join_with_cache, "
        "partial_match_rowid_merge, "
        "partial_match_table_scan, "
        "semijoin, "
        "semijoin_with_cache, "
        "subquery_cache, "
        "table_elimination, "
        "extended_keys "
       "} and val is one of {on, off, default}",
       SESSION_VAR(optimizer_switch), CMD_LINE(REQUIRED_ARG),
       optimizer_switch_names, DEFAULT(OPTIMIZER_SWITCH_DEFAULT),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(fix_optimizer_switch));

static Sys_var_charptr Sys_pid_file(
       "pid_file", "Pid file used by safe_mysqld",
       READ_ONLY GLOBAL_VAR(pidfile_name_ptr), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_plugin_dir(
       "plugin_dir", "Directory for plugins",
       READ_ONLY GLOBAL_VAR(opt_plugin_dir_ptr), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_uint Sys_port(
       "port",
       "Port number to use for connection or 0 to default to, "
       "my.cnf, $MYSQL_TCP_PORT, "
#if MYSQL_PORT_DEFAULT == 0
       "/etc/services, "
#endif
       "built-in default (" STRINGIFY_ARG(MYSQL_PORT) "), whatever comes first",
       READ_ONLY GLOBAL_VAR(mysqld_port), CMD_LINE(REQUIRED_ARG, 'P'),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulong Sys_preload_buff_size(
       "preload_buffer_size",
       "The size of the buffer that is allocated when preloading indexes",
       SESSION_VAR(preload_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024*1024*1024), DEFAULT(32768), BLOCK_SIZE(1));

static Sys_var_uint Sys_protocol_version(
       "protocol_version",
       "The version of the client/server protocol used by the MySQL server",
       READ_ONLY GLOBAL_VAR(protocol_version), NO_CMD_LINE,
       VALID_RANGE(0, ~0), DEFAULT(PROTOCOL_VERSION), BLOCK_SIZE(1));

static Sys_var_proxy_user Sys_proxy_user(
       "proxy_user", "The proxy user account name used when logging in",
       IN_SYSTEM_CHARSET);

static Sys_var_external_user Sys_exterenal_user(
       "external_user", "The external user account used when logging in",
       IN_SYSTEM_CHARSET);

static Sys_var_ulong Sys_read_buff_size(
       "read_buffer_size",
       "Each thread that does a sequential scan allocates a buffer of "
       "this size for each table it scans. If you do many sequential scans, "
       "you may want to increase this value",
       SESSION_VAR(read_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE*2, INT_MAX32), DEFAULT(128*1024),
       BLOCK_SIZE(IO_SIZE));

static bool check_read_only(sys_var *self, THD *thd, set_var *var)
{
  /* Prevent self dead-lock */
  if (thd->locked_tables_mode || thd->in_active_multi_stmt_transaction())
  {
    my_error(ER_LOCK_OR_ACTIVE_TRANSACTION, MYF(0));
    return true;
  }
  return false;
}
static bool fix_read_only(sys_var *self, THD *thd, enum_var_type type)
{
  bool result= true;
  my_bool new_read_only= read_only; // make a copy before releasing a mutex
  DBUG_ENTER("sys_var_opt_readonly::update");

  if (read_only == FALSE || read_only == opt_readonly)
  {
    opt_readonly= read_only;
    DBUG_RETURN(false);
  }

  if (check_read_only(self, thd, 0)) // just in case
    goto end;

  if (thd->global_read_lock.is_acquired())
  {
    /*
      This connection already holds the global read lock.
      This can be the case with:
      - FLUSH TABLES WITH READ LOCK
      - SET GLOBAL READ_ONLY = 1
    */
    opt_readonly= read_only;
    DBUG_RETURN(false);
  }

  /*
    READ_ONLY=1 prevents write locks from being taken on tables and
    blocks transactions from committing. We therefore should make sure
    that no such events occur while setting the read_only variable.
    This is a 2 step process:
    [1] lock_global_read_lock()
      Prevents connections from obtaining new write locks on
      tables. Note that we can still have active rw transactions.
    [2] make_global_read_lock_block_commit()
      Prevents transactions from committing.
  */

  read_only= opt_readonly;
  mysql_mutex_unlock(&LOCK_global_system_variables);

  if (thd->global_read_lock.lock_global_read_lock(thd))
    goto end_with_mutex_unlock;

  if ((result= thd->global_read_lock.make_global_read_lock_block_commit(thd)))
    goto end_with_read_lock;

  /* Change the opt_readonly system variable, safe because the lock is held */
  opt_readonly= new_read_only;
  result= false;

 end_with_read_lock:
  /* Release the lock */
  thd->global_read_lock.unlock_global_read_lock(thd);
 end_with_mutex_unlock:
  mysql_mutex_lock(&LOCK_global_system_variables);
 end:
  read_only= opt_readonly;
  DBUG_RETURN(result);
}


/**
  The read_only boolean is always equal to the opt_readonly boolean except
  during fix_read_only(); when that function is entered, opt_readonly is
  the pre-update value and read_only is the post-update value.
  fix_read_only() compares them and runs needed operations for the
  transition (especially when transitioning from false to true) and
  synchronizes both booleans in the end.
*/
static Sys_var_mybool Sys_readonly(
       "read_only",
       "Make all non-temporary tables read-only, with the exception for "
       "replication (slave) threads and users with the SUPER privilege",
       GLOBAL_VAR(read_only), CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_read_only), ON_UPDATE(fix_read_only));

// Small lower limit to be able to test MRR
static Sys_var_ulong Sys_read_rnd_buff_size(
       "read_rnd_buffer_size",
       "When reading rows in sorted order after a sort, the rows are read "
       "through this buffer to avoid a disk seeks",
       SESSION_VAR(read_rnd_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, INT_MAX32), DEFAULT(256*1024), BLOCK_SIZE(1));

static Sys_var_ulong Sys_div_precincrement(
       "div_precision_increment", "Precision of the result of '/' "
       "operator will be increased on that value",
       SESSION_VAR(div_precincrement), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, DECIMAL_MAX_SCALE), DEFAULT(4), BLOCK_SIZE(1));

static Sys_var_ulong Sys_rpl_recovery_rank(
       "rpl_recovery_rank", "Unused, will be removed",
       GLOBAL_VAR(rpl_recovery_rank), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static Sys_var_ulong Sys_range_alloc_block_size(
       "range_alloc_block_size",
       "Allocation block size for storing ranges during optimization",
       SESSION_VAR(range_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(RANGE_ALLOC_BLOCK_SIZE, UINT_MAX),
       DEFAULT(RANGE_ALLOC_BLOCK_SIZE), BLOCK_SIZE(1024));

static Sys_var_ulong Sys_multi_range_count(
       "multi_range_count", "Ignored. Use mrr_buffer_size instead",
       SESSION_VAR(multi_range_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(256), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED("'@@mrr_buffer_size'"));

static bool fix_thd_mem_root(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    reset_root_defaults(thd->mem_root,
                        thd->variables.query_alloc_block_size,
                        thd->variables.query_prealloc_size);
  return false;
}
static Sys_var_ulong Sys_query_alloc_block_size(
       "query_alloc_block_size",
       "Allocation block size for query parsing and execution",
       SESSION_VAR(query_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, UINT_MAX), DEFAULT(QUERY_ALLOC_BLOCK_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_thd_mem_root));

static Sys_var_ulong Sys_query_prealloc_size(
       "query_prealloc_size",
       "Persistent buffer for query parsing and execution",
       SESSION_VAR(query_prealloc_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(QUERY_ALLOC_PREALLOC_SIZE, UINT_MAX),
       DEFAULT(QUERY_ALLOC_PREALLOC_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_thd_mem_root));

#ifdef HAVE_SMEM
static Sys_var_mybool Sys_shared_memory(
       "shared_memory", "Enable the shared memory",
       READ_ONLY GLOBAL_VAR(opt_enable_shared_memory), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_charptr Sys_shared_memory_base_name(
       "shared_memory_base_name", "Base name of shared memory",
       READ_ONLY GLOBAL_VAR(shared_memory_base_name), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));
#endif

// this has to be NO_CMD_LINE as the command-line option has a different name
static Sys_var_mybool Sys_skip_external_locking(
       "skip_external_locking", "Don't use system (external) locking",
       READ_ONLY GLOBAL_VAR(my_disable_locking), NO_CMD_LINE, DEFAULT(TRUE));

static Sys_var_mybool Sys_skip_networking(
       "skip_networking", "Don't allow connection with TCP/IP",
       READ_ONLY GLOBAL_VAR(opt_disable_networking), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_mybool Sys_skip_name_resolve(
       "skip_name_resolve",
       "Don't resolve hostnames. All hostnames are IP's or 'localhost'.",
       READ_ONLY GLOBAL_VAR(opt_skip_name_resolve),
       CMD_LINE(OPT_ARG, OPT_SKIP_RESOLVE),
       DEFAULT(FALSE));

static Sys_var_mybool Sys_skip_show_database(
       "skip_show_database", "Don't allow 'SHOW DATABASE' commands",
       READ_ONLY GLOBAL_VAR(opt_skip_show_db), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_charptr Sys_socket(
       "socket", "Socket file to use for connection",
       READ_ONLY GLOBAL_VAR(mysqld_unix_port), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

/* 
  thread_concurrency is a no-op on all platforms since
  MySQL 5.1.  It will be removed in the context of
  WL#5265
*/
static Sys_var_ulong Sys_thread_concurrency(
       "thread_concurrency",
       "Permits the application to give the threads system a hint for "
       "the desired number of threads that should be run at the same time."
       "This variable has no effect, and is deprecated. "
       "It will be removed in a future release.",
       READ_ONLY GLOBAL_VAR(concurrency),
       CMD_LINE(REQUIRED_ARG, OPT_THREAD_CONCURRENCY),
       VALID_RANGE(1, 512), DEFAULT(DEFAULT_CONCURRENCY), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static Sys_var_ulonglong Sys_thread_stack(
       "thread_stack", "The stack size for each thread",
       READ_ONLY GLOBAL_VAR(my_thread_stack_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(128*1024, ULONGLONG_MAX), DEFAULT(DEFAULT_THREAD_STACK),
       BLOCK_SIZE(1024));

static Sys_var_charptr Sys_tmpdir(
       "tmpdir", "Path for temporary files. Several paths may "
       "be specified, separated by a "
#if defined(__WIN__)
       "semicolon (;)"
#else
       "colon (:)"
#endif
       ", in this case they are used in a round-robin fashion",
       READ_ONLY GLOBAL_VAR(opt_mysql_tmpdir), CMD_LINE(REQUIRED_ARG, 't'),
       IN_FS_CHARSET, DEFAULT(0));

static bool fix_trans_mem_root(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    reset_root_defaults(&thd->transaction.mem_root,
                        thd->variables.trans_alloc_block_size,
                        thd->variables.trans_prealloc_size);
  return false;
}
static Sys_var_ulong Sys_trans_alloc_block_size(
       "transaction_alloc_block_size",
       "Allocation block size for transactions to be stored in binary log",
       SESSION_VAR(trans_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 128 * 1024 * 1024), DEFAULT(QUERY_ALLOC_BLOCK_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_trans_mem_root));

static Sys_var_ulong Sys_trans_prealloc_size(
       "transaction_prealloc_size",
       "Persistent buffer for transactions to be stored in binary log",
       SESSION_VAR(trans_prealloc_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 128 * 1024 * 1024), DEFAULT(TRANS_ALLOC_PREALLOC_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_trans_mem_root));

static const char *thread_handling_names[]=
{
  "one-thread-per-connection", "no-threads",
#ifdef HAVE_POOL_OF_THREADS
  "pool-of-threads",
#endif
  0
};

#if defined (_WIN32) && defined (HAVE_POOL_OF_THREADS)
/* Windows is using OS threadpool, so we're pretty sure it works well */
#define DEFAULT_THREAD_HANDLING 2
#else
#define DEFAULT_THREAD_HANDLING 0
#endif

static Sys_var_enum Sys_thread_handling(
       "thread_handling",
       "Define threads usage for handling queries, one of "
       "one-thread-per-connection, no-threads"
#ifdef HAVE_POOL_OF_THREADS
       ", pool-of-threads"
#endif
       , READ_ONLY GLOBAL_VAR(thread_handling), CMD_LINE(REQUIRED_ARG),
       thread_handling_names, 
       DEFAULT(DEFAULT_THREAD_HANDLING)
 );

#ifdef HAVE_QUERY_CACHE
static bool check_query_cache_size(sys_var *self, THD *thd, set_var *var)
{
  if (global_system_variables.query_cache_type == 0 &&
      var->value && var->value->val_int() != 0)
  {
    my_error(ER_QUERY_CACHE_DISABLED, MYF(0));
    return true;
  }

  return false;
}
static bool fix_query_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
  ulong new_cache_size= query_cache.resize(query_cache_size);
  /*
     Note: query_cache_size is a global variable reflecting the
     requested cache size. See also query_cache_size_arg
  */
  if (query_cache_size != new_cache_size)
    push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                        ER_WARN_QC_RESIZE, ER(ER_WARN_QC_RESIZE),
                        query_cache_size, new_cache_size);

  query_cache_size= new_cache_size;
  return false;
}
static Sys_var_ulonglong Sys_query_cache_size(
       "query_cache_size",
       "The memory allocated to store results from old queries",
       GLOBAL_VAR(query_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1024),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_query_cache_size),
       ON_UPDATE(fix_query_cache_size));

static Sys_var_ulong Sys_query_cache_limit(
       "query_cache_limit",
       "Don't cache results that are bigger than this",
       GLOBAL_VAR(query_cache.query_cache_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(1024*1024), BLOCK_SIZE(1));

static bool fix_qcache_min_res_unit(sys_var *self, THD *thd, enum_var_type type)
{
  query_cache_min_res_unit=
    query_cache.set_min_res_unit(query_cache_min_res_unit);
  return false;
}
static Sys_var_ulong Sys_query_cache_min_res_unit(
       "query_cache_min_res_unit",
       "The minimum size for blocks allocated by the query cache",
       GLOBAL_VAR(query_cache_min_res_unit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(QUERY_CACHE_MIN_RESULT_DATA_SIZE),
       BLOCK_SIZE(8), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_qcache_min_res_unit));

static const char *query_cache_type_names[]= { "OFF", "ON", "DEMAND", 0 };
static bool check_query_cache_type(sys_var *self, THD *thd, set_var *var)
{
  if (query_cache.is_disable_in_progress())
  {
    my_error(ER_QUERY_CACHE_IS_DISABLED, MYF(0));
    return true;
  }
  if (var->type != OPT_GLOBAL &&
      global_system_variables.query_cache_type == 0 &&
      var->value->val_int() != 0)
  {
    my_error(ER_QUERY_CACHE_IS_GLOBALY_DISABLED, MYF(0));
    return true;
  }

  return false;
}
static bool fix_query_cache_type(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    return false;

  if (global_system_variables.query_cache_type != 0 &&
      query_cache.is_disabled())
  {
    /* if disabling in progress variable will not be set */
    DBUG_ASSERT(!query_cache.is_disable_in_progress());
    /* Enable query cache because it was disabled */
    fix_query_cache_size(0, thd, type);
  }
  else if (global_system_variables.query_cache_type == 0)
    query_cache.disable_query_cache(thd);
  return false;
}
static Sys_var_enum Sys_query_cache_type(
       "query_cache_type",
       "OFF = Don't cache or retrieve results. ON = Cache all results "
       "except SELECT SQL_NO_CACHE ... queries. DEMAND = Cache only "
       "SELECT SQL_CACHE ... queries",
       SESSION_VAR(query_cache_type), CMD_LINE(REQUIRED_ARG),
       query_cache_type_names, DEFAULT(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_query_cache_type),
       ON_UPDATE(fix_query_cache_type));

static Sys_var_mybool Sys_query_cache_wlock_invalidate(
       "query_cache_wlock_invalidate",
       "Invalidate queries in query cache on LOCK for write",
       SESSION_VAR(query_cache_wlock_invalidate), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));
#endif /* HAVE_QUERY_CACHE */

static Sys_var_mybool Sys_secure_auth(
       "secure_auth",
       "Disallow authentication for accounts that have old (pre-4.1) "
       "passwords",
       GLOBAL_VAR(opt_secure_auth), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_charptr Sys_secure_file_priv(
       "secure_file_priv",
       "Limit LOAD DATA, SELECT ... OUTFILE, and LOAD_FILE() to files "
       "within specified directory",
       PREALLOCATED READ_ONLY GLOBAL_VAR(opt_secure_file_priv),
       CMD_LINE(REQUIRED_ARG), IN_FS_CHARSET, DEFAULT(0));

static bool fix_server_id(sys_var *self, THD *thd, enum_var_type type)
{
  server_id_supplied = 1;
  thd->server_id= server_id;
  return false;
}
static Sys_var_ulong Sys_server_id(
       "server_id",
       "Uniquely identifies the server instance in the community of "
       "replication partners",
       GLOBAL_VAR(server_id), CMD_LINE(REQUIRED_ARG, OPT_SERVER_ID),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_server_id));

static Sys_var_mybool Sys_slave_compressed_protocol(
       "slave_compressed_protocol",
       "Use compression on master/slave protocol",
       GLOBAL_VAR(opt_slave_compressed_protocol), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

#ifdef HAVE_REPLICATION
static const char *slave_exec_mode_names[]= {"STRICT", "IDEMPOTENT", 0};
static Sys_var_enum Slave_exec_mode(
       "slave_exec_mode",
       "Modes for how replication events should be executed. Legal values "
       "are STRICT (default) and IDEMPOTENT. In IDEMPOTENT mode, "
       "replication will not stop for operations that are idempotent. "
       "In STRICT mode, replication will stop on any unexpected difference "
       "between the master and the slave",
       GLOBAL_VAR(slave_exec_mode_options), CMD_LINE(REQUIRED_ARG),
       slave_exec_mode_names, DEFAULT(SLAVE_EXEC_MODE_STRICT));

static const char *slave_type_conversions_name[]= {"ALL_LOSSY", "ALL_NON_LOSSY", 0};
static Sys_var_set Slave_type_conversions(
       "slave_type_conversions",
       "Set of slave type conversions that are enabled. Legal values are:"
       " ALL_LOSSY to enable lossy conversions and"
       " ALL_NON_LOSSY to enable non-lossy conversions."
       " If the variable is assigned the empty set, no conversions are"
       " allowed and it is expected that the types match exactly.",
       GLOBAL_VAR(slave_type_conversions_options), CMD_LINE(REQUIRED_ARG),
       slave_type_conversions_name,
       DEFAULT(0));

static Sys_var_mybool Sys_slave_sql_verify_checksum(
       "slave_sql_verify_checksum",
       "Force checksum verification of replication events after reading them "
       "from relay log. Note: Events are always checksum-verified by slave on "
       "receiving them from the network before writing them to the relay log",
       GLOBAL_VAR(opt_slave_sql_verify_checksum), CMD_LINE(OPT_ARG),
       DEFAULT(TRUE));

static Sys_var_mybool Sys_master_verify_checksum(
       "master_verify_checksum",
       "Force checksum verification of logged events in the binary log before "
       "sending them to slaves or printing them in the output of "
       "SHOW BINLOG EVENTS",
       GLOBAL_VAR(opt_master_verify_checksum), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

/* These names must match RPL_SKIP_XXX #defines in slave.h. */
static const char *replicate_events_marked_for_skip_names[]= {
  "replicate", "filter_on_slave", "filter_on_master", 0
};
static bool
replicate_events_marked_for_skip_check(sys_var *self, THD *thd,
                                                set_var *var)
{
  int thread_mask;
  DBUG_ENTER("sys_var_replicate_events_marked_for_skip_check");

  /* Slave threads must be stopped to change the variable. */
  mysql_mutex_lock(&LOCK_active_mi);
  lock_slave_threads(active_mi);
  init_thread_mask(&thread_mask, active_mi, 0 /*not inverse*/);
  unlock_slave_threads(active_mi);
  mysql_mutex_unlock(&LOCK_active_mi);

  if (thread_mask) // We refuse if any slave thread is running
  {
    my_error(ER_SLAVE_MUST_STOP, MYF(0));
    DBUG_RETURN(true);
  }
  DBUG_RETURN(false);
}
bool
Sys_var_replicate_events_marked_for_skip::global_update(THD *thd, set_var *var)
{
  bool result;
  int thread_mask;
  DBUG_ENTER("Sys_var_replicate_events_marked_for_skip::global_update");

  /* Slave threads must be stopped to change the variable. */
  mysql_mutex_lock(&LOCK_active_mi);
  lock_slave_threads(active_mi);
  init_thread_mask(&thread_mask, active_mi, 0 /*not inverse*/);
  if (thread_mask) // We refuse if any slave thread is running
  {
    my_error(ER_SLAVE_MUST_STOP, MYF(0));
    result= true;
  }
  else
    result= Sys_var_enum::global_update(thd, var);

  unlock_slave_threads(active_mi);
  mysql_mutex_unlock(&LOCK_active_mi);
  DBUG_RETURN(result);
}
static Sys_var_replicate_events_marked_for_skip Replicate_events_marked_for_skip
   ("replicate_events_marked_for_skip",
   "Whether the slave should replicate events that were created with "
   "@@skip_replication=1 on the master. Default REPLICATE (no events are "
   "skipped). Other values are FILTER_ON_SLAVE (events will be sent by the "
   "master but ignored by the slave) and FILTER_ON_MASTER (events marked with "
   "@@skip_replication=1 will be filtered on the master and never be sent to "
   "the slave).",
   GLOBAL_VAR(opt_replicate_events_marked_for_skip), CMD_LINE(REQUIRED_ARG),
   replicate_events_marked_for_skip_names, DEFAULT(RPL_SKIP_REPLICATE),
   NO_MUTEX_GUARD, NOT_IN_BINLOG,
   ON_CHECK(replicate_events_marked_for_skip_check));
#endif


static Sys_var_ulong Sys_slow_launch_time(
       "slow_launch_time",
       "If creating the thread takes longer than this value (in seconds), "
       "the Slow_launch_threads counter will be incremented",
       GLOBAL_VAR(slow_launch_time), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, LONG_TIMEOUT), DEFAULT(2), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_sort_buffer(
       "sort_buffer_size",
       "Each thread that needs to do a sort allocates a buffer of this size",
       SESSION_VAR(sortbuff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(MIN_SORT_MEMORY, SIZE_T_MAX), DEFAULT(MAX_SORT_MEMORY),
       BLOCK_SIZE(1));

export ulonglong expand_sql_mode(ulonglong sql_mode)
{
  if (sql_mode & MODE_ANSI)
  {
    /*
      Note that we dont set
      MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS | MODE_NO_FIELD_OPTIONS
      to allow one to get full use of MySQL in this mode.

      MODE_ONLY_FULL_GROUP_BY was removed from ANSI mode because it is
      currently overly restrictive (see BUG#8510).
    */
    sql_mode|= (MODE_REAL_AS_FLOAT | MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE);
  }
  if (sql_mode & MODE_ORACLE)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS | MODE_NO_AUTO_CREATE_USER);
  if (sql_mode & MODE_MSSQL)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_POSTGRESQL)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_DB2)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_MAXDB)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS | MODE_NO_AUTO_CREATE_USER);
  if (sql_mode & MODE_MYSQL40)
    sql_mode|= MODE_HIGH_NOT_PRECEDENCE;
  if (sql_mode & MODE_MYSQL323)
    sql_mode|= MODE_HIGH_NOT_PRECEDENCE;
  if (sql_mode & MODE_TRADITIONAL)
    sql_mode|= (MODE_STRICT_TRANS_TABLES | MODE_STRICT_ALL_TABLES |
                MODE_NO_ZERO_IN_DATE | MODE_NO_ZERO_DATE |
                MODE_ERROR_FOR_DIVISION_BY_ZERO | MODE_NO_AUTO_CREATE_USER |
                MODE_NO_ENGINE_SUBSTITUTION);
  return sql_mode;
}
static bool check_sql_mode(sys_var *self, THD *thd, set_var *var)
{
  var->save_result.ulonglong_value=
    expand_sql_mode(var->save_result.ulonglong_value);
  return false;
}
static bool fix_sql_mode(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
  {
    /* Update thd->server_status */
    if (thd->variables.sql_mode & MODE_NO_BACKSLASH_ESCAPES)
      thd->server_status|= SERVER_STATUS_NO_BACKSLASH_ESCAPES;
    else
      thd->server_status&= ~SERVER_STATUS_NO_BACKSLASH_ESCAPES;
    if (thd->variables.sql_mode & MODE_ANSI_QUOTES)
      thd->server_status|= SERVER_STATUS_ANSI_QUOTES;
    else
      thd->server_status&= ~SERVER_STATUS_ANSI_QUOTES;
  }
  return false;
}
/*
  WARNING: When adding new SQL modes don't forget to update the
  tables definitions that stores it's value (ie: mysql.event, mysql.proc)
*/
static const char *sql_mode_names[]=
{
  "REAL_AS_FLOAT", "PIPES_AS_CONCAT", "ANSI_QUOTES", "IGNORE_SPACE",
  "IGNORE_BAD_TABLE_OPTIONS",
  "ONLY_FULL_GROUP_BY", "NO_UNSIGNED_SUBTRACTION", "NO_DIR_IN_CREATE",
  "POSTGRESQL", "ORACLE", "MSSQL", "DB2", "MAXDB", "NO_KEY_OPTIONS",
  "NO_TABLE_OPTIONS", "NO_FIELD_OPTIONS", "MYSQL323", "MYSQL40", "ANSI",
  "NO_AUTO_VALUE_ON_ZERO", "NO_BACKSLASH_ESCAPES", "STRICT_TRANS_TABLES",
  "STRICT_ALL_TABLES", "NO_ZERO_IN_DATE", "NO_ZERO_DATE",
  "ALLOW_INVALID_DATES", "ERROR_FOR_DIVISION_BY_ZERO", "TRADITIONAL",
  "NO_AUTO_CREATE_USER", "HIGH_NOT_PRECEDENCE", "NO_ENGINE_SUBSTITUTION",
  "PAD_CHAR_TO_FULL_LENGTH",
  0
};
export bool sql_mode_string_representation(THD *thd, ulonglong sql_mode,
                                           LEX_STRING *ls)
{
  set_to_string(thd, ls, sql_mode, sql_mode_names);
  return ls->str == 0;
}
/*
  sql_mode should *not* be IN_BINLOG: even though it is written to the binlog,
  the slave ignores the MODE_NO_DIR_IN_CREATE variable, so slave's value
  differs from master's (see log_event.cc: Query_log_event::do_apply_event()).
*/
static Sys_var_set Sys_sql_mode(
       "sql_mode",
       "Syntax: sql-mode=mode[,mode[,mode...]]. See the manual for the "
       "complete list of valid sql modes",
       SESSION_VAR(sql_mode), CMD_LINE(REQUIRED_ARG),
       sql_mode_names, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_sql_mode), ON_UPDATE(fix_sql_mode));

static const char *old_mode_names[]=
{
  "NO_DUP_KEY_WARNINGS_WITH_IGNORE", "NO_PROGRESS_INFO",
  0
};

export bool old_mode_string_representation(THD *thd, ulonglong sql_mode,
                                           LEX_STRING *ls)
{
  set_to_string(thd, ls, sql_mode, old_mode_names);
  return ls->str == 0;
}
/*
  sql_mode should *not* be IN_BINLOG as the slave can't remember this
  anyway on restart.
*/
static Sys_var_set Sys_old_behavior(
       "old_mode",
       "Used to emulate old behavior from earlier MariaDB or MySQL versions. "
       "Syntax: old_mode=mode[,mode[,mode...]]. "
       "See the manual for the complete list of valid old modes",
       SESSION_VAR(old_behavior), CMD_LINE(REQUIRED_ARG),
       old_mode_names, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG);

#if defined(HAVE_OPENSSL) && !defined(EMBEDDED_LIBRARY)
#define SSL_OPT(X) CMD_LINE(REQUIRED_ARG,X)
#else
#define SSL_OPT(X) NO_CMD_LINE
#endif

static Sys_var_charptr Sys_ssl_ca(
       "ssl_ca",
       "CA file in PEM format (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_ca), SSL_OPT(OPT_SSL_CA),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_capath(
       "ssl_capath",
       "CA directory (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_capath), SSL_OPT(OPT_SSL_CAPATH),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_cert(
       "ssl_cert", "X509 cert in PEM format (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_cert), SSL_OPT(OPT_SSL_CERT),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_cipher(
       "ssl_cipher", "SSL cipher to use (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_cipher), SSL_OPT(OPT_SSL_CIPHER),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_key(
       "ssl_key", "X509 key in PEM format (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_key), SSL_OPT(OPT_SSL_KEY),
       IN_FS_CHARSET, DEFAULT(0));

// why ENUM and not BOOL ?
static const char *updatable_views_with_limit_names[]= {"NO", "YES", 0};
static Sys_var_enum Sys_updatable_views_with_limit(
       "updatable_views_with_limit",
       "YES = Don't issue an error message (warning only) if a VIEW without "
       "presence of a key of the underlying table is used in queries with a "
       "LIMIT clause for updating. NO = Prohibit update of a VIEW, which "
       "does not contain a key of the underlying table and the query uses "
       "a LIMIT clause (usually get from GUI tools)",
       SESSION_VAR(updatable_views_with_limit), CMD_LINE(REQUIRED_ARG),
       updatable_views_with_limit_names, DEFAULT(TRUE));

static Sys_var_mybool Sys_sync_frm(
       "sync_frm", "Sync .frm files to disk on creation",
       GLOBAL_VAR(opt_sync_frm), CMD_LINE(OPT_ARG),
       DEFAULT(TRUE));

static char *system_time_zone_ptr;
static Sys_var_charptr Sys_system_time_zone(
       "system_time_zone", "The server system time zone",
       READ_ONLY GLOBAL_VAR(system_time_zone_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(system_time_zone));

static Sys_var_ulong Sys_table_def_size(
       "table_definition_cache",
       "The number of cached table definitions",
       GLOBAL_VAR(table_def_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(TABLE_DEF_CACHE_MIN, 512*1024),
       DEFAULT(TABLE_DEF_CACHE_DEFAULT), BLOCK_SIZE(1));

static Sys_var_ulong Sys_table_cache_size(
       "table_open_cache", "The number of cached open tables",
       GLOBAL_VAR(table_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 512*1024), DEFAULT(TABLE_OPEN_CACHE_DEFAULT),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_thread_cache_size(
       "thread_cache_size",
       "How many threads we should keep in a cache for reuse",
       GLOBAL_VAR(thread_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 16384), DEFAULT(0), BLOCK_SIZE(1));

#ifdef HAVE_POOL_OF_THREADS
static bool fix_tp_max_threads(sys_var *, THD *, enum_var_type)
{
#ifdef _WIN32
  tp_set_max_threads(threadpool_max_threads);
#endif
  return false;
}


#ifdef _WIN32
static bool fix_tp_min_threads(sys_var *, THD *, enum_var_type)
{
  tp_set_min_threads(threadpool_min_threads);
  return false;
}
#endif


#ifndef  _WIN32
static bool check_threadpool_size(sys_var *self, THD *thd, set_var *var)
{
  ulonglong v= var->save_result.ulonglong_value;
  if (v > threadpool_max_size)
  {
    var->save_result.ulonglong_value= threadpool_max_size;
    return throw_bounds_warning(thd, self->name.str, true, true, v);
  }
  return false;
}


static bool fix_threadpool_size(sys_var*, THD*, enum_var_type)
{
  tp_set_threadpool_size(threadpool_size);
  return false;
}


static bool fix_threadpool_stall_limit(sys_var*, THD*, enum_var_type)
{
  tp_set_threadpool_stall_limit(threadpool_stall_limit);
  return false;
}
#endif

#ifdef _WIN32
static Sys_var_uint Sys_threadpool_min_threads(
  "thread_pool_min_threads",
  "Minimum number of threads in the thread pool.",
  GLOBAL_VAR(threadpool_min_threads), CMD_LINE(REQUIRED_ARG),
  VALID_RANGE(1, 256), DEFAULT(1), BLOCK_SIZE(1),
  NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
  ON_UPDATE(fix_tp_min_threads)
  );
#else
static Sys_var_uint Sys_threadpool_idle_thread_timeout(
  "thread_pool_idle_timeout",
  "Timeout in seconds for an idle thread in the thread pool."
  "Worker thread will be shut down after timeout",
  GLOBAL_VAR(threadpool_idle_timeout), CMD_LINE(REQUIRED_ARG),
  VALID_RANGE(1, UINT_MAX), DEFAULT(60), BLOCK_SIZE(1)
);
static Sys_var_uint Sys_threadpool_oversubscribe(
  "thread_pool_oversubscribe",
  "How many additional active worker threads in a group are allowed.",
  GLOBAL_VAR(threadpool_oversubscribe), CMD_LINE(REQUIRED_ARG),
  VALID_RANGE(1, 1000), DEFAULT(3), BLOCK_SIZE(1)
);
static Sys_var_uint Sys_threadpool_size(
 "thread_pool_size",
 "Number of thread groups in the pool. "
 "This parameter is roughly equivalent to maximum number of concurrently "
 "executing threads (threads in a waiting state do not count as executing).",
  GLOBAL_VAR(threadpool_size), CMD_LINE(REQUIRED_ARG),
  VALID_RANGE(1, MAX_THREAD_GROUPS), DEFAULT(my_getncpus()), BLOCK_SIZE(1),
  NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_threadpool_size),
  ON_UPDATE(fix_threadpool_size)
);
static Sys_var_uint Sys_threadpool_stall_limit(
 "thread_pool_stall_limit",
 "Maximum query execution time in milliseconds,"
 "before an executing non-yielding thread is considered stalled."
 "If a worker thread is stalled, additional worker thread "
 "may be created to handle remaining clients.",
  GLOBAL_VAR(threadpool_stall_limit), CMD_LINE(REQUIRED_ARG),
  VALID_RANGE(10, UINT_MAX), DEFAULT(500), BLOCK_SIZE(1),
  NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), 
  ON_UPDATE(fix_threadpool_stall_limit)
);
#endif /* !WIN32 */
static Sys_var_uint Sys_threadpool_max_threads(
  "thread_pool_max_threads",
  "Maximum allowed number of worker threads in the thread pool",
   GLOBAL_VAR(threadpool_max_threads), CMD_LINE(REQUIRED_ARG),
   VALID_RANGE(1, 65536), DEFAULT(500), BLOCK_SIZE(1),
   NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), 
   ON_UPDATE(fix_tp_max_threads)
);
#endif /* HAVE_POOL_OF_THREADS */

/**
  Can't change the 'next' tx_isolation if we are already in a
  transaction.
*/

static bool check_tx_isolation(sys_var *self, THD *thd, set_var *var)
{
  if (var->type == OPT_DEFAULT && thd->in_active_multi_stmt_transaction())
  {
    DBUG_ASSERT(thd->in_multi_stmt_transaction_mode());
    my_error(ER_CANT_CHANGE_TX_ISOLATION, MYF(0));
    return TRUE;
  }
  return FALSE;
}

// NO_CMD_LINE - different name of the option
static Sys_var_tx_isolation Sys_tx_isolation(
       "tx_isolation", "Default transaction isolation level",
       SESSION_VAR(tx_isolation), NO_CMD_LINE,
       tx_isolation_names, DEFAULT(ISO_REPEATABLE_READ),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_tx_isolation));

static Sys_var_ulonglong Sys_tmp_table_size(
       "tmp_table_size",
       "If an internal in-memory temporary table exceeds this size, MySQL "
       "will automatically convert it to an on-disk MyISAM or Aria table",
       SESSION_VAR(tmp_table_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, (ulonglong)~(intptr)0), DEFAULT(16*1024*1024),
       BLOCK_SIZE(1));

static Sys_var_mybool Sys_timed_mutexes(
       "timed_mutexes",
       "Specify whether to time mutexes. Deprecated, has no effect.",
       GLOBAL_VAR(timed_mutexes), CMD_LINE(OPT_ARG), DEFAULT(0),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL), ON_UPDATE(NULL),
       DEPRECATED(""));

static char *server_version_ptr;
static Sys_var_charptr Sys_version(
       "version", "Server version",
       READ_ONLY GLOBAL_VAR(server_version_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(server_version));

static char *server_version_comment_ptr;
static Sys_var_charptr Sys_version_comment(
       "version_comment", "version_comment",
       READ_ONLY GLOBAL_VAR(server_version_comment_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(MYSQL_COMPILATION_COMMENT));

static char *server_version_compile_machine_ptr;
static Sys_var_charptr Sys_version_compile_machine(
       "version_compile_machine", "version_compile_machine",
       READ_ONLY GLOBAL_VAR(server_version_compile_machine_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(MACHINE_TYPE));

static char *server_version_compile_os_ptr;
static Sys_var_charptr Sys_version_compile_os(
       "version_compile_os", "version_compile_os",
       READ_ONLY GLOBAL_VAR(server_version_compile_os_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(SYSTEM_TYPE));

static Sys_var_ulong Sys_net_wait_timeout(
       "wait_timeout",
       "The number of seconds the server waits for activity on a "
       "connection before closing it",
       SESSION_VAR(net_wait_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, IF_WIN(INT_MAX32/1000, LONG_TIMEOUT)),
       DEFAULT(NET_WAIT_TIMEOUT), BLOCK_SIZE(1));

/** propagates changes to the relevant flag of @@optimizer_switch */
static bool fix_engine_condition_pushdown(sys_var *self, THD *thd,
                                          enum_var_type type)
{
  SV *sv= (type == OPT_GLOBAL) ? &global_system_variables : &thd->variables;
  if (sv->engine_condition_pushdown)
    sv->optimizer_switch|= OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN;
  else
    sv->optimizer_switch&= ~OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN;
  return false;
}
static Sys_var_mybool Sys_engine_condition_pushdown(
       "engine_condition_pushdown",
       "Push supported query conditions to the storage engine."
       " Deprecated, use --optimizer-switch instead.",
       SESSION_VAR(engine_condition_pushdown),
       CMD_LINE(OPT_ARG, OPT_ENGINE_CONDITION_PUSHDOWN),
       DEFAULT(TRUE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(fix_engine_condition_pushdown),
       DEPRECATED("'@@optimizer_switch'"));

static Sys_var_plugin Sys_default_storage_engine(
       "default_storage_engine", "The default storage engine for new tables",
       SESSION_VAR(table_plugin), NO_CMD_LINE,
       MYSQL_STORAGE_ENGINE_PLUGIN, DEFAULT(&default_storage_engine),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_not_null));

//  Alias for @@default_storage_engine
static Sys_var_plugin Sys_storage_engine(
       "storage_engine", "Alias for @@default_storage_engine. Deprecated",
       SESSION_VAR(table_plugin), NO_CMD_LINE,
       MYSQL_STORAGE_ENGINE_PLUGIN, DEFAULT(&default_storage_engine),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_not_null));

#if defined(ENABLED_DEBUG_SYNC)
/*
  Variable can be set for the session only.

  This could be changed later. Then we need to have a global array of
  actions in addition to the thread local ones. SET GLOBAL would
  manage the global array, SET [SESSION] the local array. A sync point
  would need to look for a local and a global action. Setting and
  executing of global actions need to be protected by a mutex.

  The purpose of global actions could be to allow synchronizing with
  connectionless threads that cannot execute SET statements.
*/
static Sys_var_debug_sync Sys_debug_sync(
       "debug_sync", "Debug Sync Facility",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_has_super));
#endif /* defined(ENABLED_DEBUG_SYNC) */

/**
 "time_format" "date_format" "datetime_format"

  the following three variables are unused, and the source of confusion
  (bug reports like "I've changed date_format, but date format hasn't changed.
  I've made them read-only, to alleviate the situation somewhat.

  @todo make them NO_CMD_LINE ?
*/
static Sys_var_charptr Sys_date_format(
       "date_format", "The DATE format (ignored)",
       READ_ONLY GLOBAL_VAR(global_date_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].date_format));

static Sys_var_charptr Sys_datetime_format(
       "datetime_format", "The DATETIME format (ignored)",
       READ_ONLY GLOBAL_VAR(global_datetime_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].datetime_format));

static Sys_var_charptr Sys_time_format(
       "time_format", "The TIME format (ignored)",
       READ_ONLY GLOBAL_VAR(global_time_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].time_format));

static bool fix_autocommit(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_GLOBAL)
  {
    if (global_system_variables.option_bits & OPTION_AUTOCOMMIT)
      global_system_variables.option_bits&= ~OPTION_NOT_AUTOCOMMIT;
    else
      global_system_variables.option_bits|= OPTION_NOT_AUTOCOMMIT;
    return false;
  }

  if (thd->variables.option_bits & OPTION_AUTOCOMMIT &&
      thd->variables.option_bits & OPTION_NOT_AUTOCOMMIT)
  { // activating autocommit

    if (trans_commit_stmt(thd) || trans_commit(thd))
    {
      thd->variables.option_bits&= ~OPTION_AUTOCOMMIT;
      return true;
    }
    /*
      Don't close thread tables or release metadata locks: if we do so, we
      risk releasing locks/closing tables of expressions used to assign
      other variables, as in:
      set @var=my_stored_function1(), @@autocommit=1, @var2=(select max(a)
      from my_table), ...
      The locks will be released at statement end anyway, as SET
      statement that assigns autocommit is marked to commit
      transaction implicitly at the end (@sa stmt_causes_implicitcommit()).
    */
    thd->variables.option_bits&=
                 ~(OPTION_BEGIN | OPTION_KEEP_LOG | OPTION_NOT_AUTOCOMMIT);
    thd->transaction.all.modified_non_trans_table= false;
    thd->server_status|= SERVER_STATUS_AUTOCOMMIT;
    return false;
  }

  if (!(thd->variables.option_bits & OPTION_AUTOCOMMIT) &&
      !(thd->variables.option_bits & OPTION_NOT_AUTOCOMMIT))
  { // disabling autocommit

    thd->transaction.all.modified_non_trans_table= false;
    thd->server_status&= ~SERVER_STATUS_AUTOCOMMIT;
    thd->variables.option_bits|= OPTION_NOT_AUTOCOMMIT;
    return false;
  }

  return false; // autocommit value wasn't changed
}
static Sys_var_bit Sys_autocommit(
       "autocommit", "autocommit",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_AUTOCOMMIT, DEFAULT(TRUE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_autocommit));
export sys_var *Sys_autocommit_ptr= &Sys_autocommit; // for sql_yacc.yy

static Sys_var_mybool Sys_big_tables(
       "big_tables", "Allow big result sets by saving all "
       "temporary sets on file (Solves most 'table full' errors)",
       SESSION_VAR(big_tables), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

#ifndef TO_BE_DELETED   /* Alias for big_tables */
static Sys_var_mybool Sys_sql_big_tables(
       "sql_big_tables", "alias for big_tables",
       SESSION_VAR(big_tables), NO_CMD_LINE, DEFAULT(FALSE));
#endif

static Sys_var_bit Sys_big_selects(
       "sql_big_selects", "sql_big_selects",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_BIG_SELECTS,
       DEFAULT(FALSE));

static Sys_var_bit Sys_log_off(
       "sql_log_off", "sql_log_off",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_LOG_OFF,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_has_super));

/**
  This function sets the session variable thd->variables.sql_log_bin 
  to reflect changes to @@session.sql_log_bin.

  @param[IN] self   A pointer to the sys_var, i.e. Sys_log_binlog.
  @param[IN] type   The type either session or global.

  @return @c FALSE.
*/
static bool fix_sql_log_bin_after_update(sys_var *self, THD *thd,
                                         enum_var_type type)
{
  DBUG_ASSERT(type == OPT_SESSION);

  if (thd->variables.sql_log_bin)
    thd->variables.option_bits |= OPTION_BIN_LOG;
  else
    thd->variables.option_bits &= ~OPTION_BIN_LOG;

  return FALSE;
}

/**
  This function checks if the sql_log_bin can be changed,
  what is possible if:
    - the user is a super user;
    - the set is not called from within a function/trigger;
    - there is no on-going transaction.

  @param[IN] self   A pointer to the sys_var, i.e. Sys_log_binlog.
  @param[IN] var    A pointer to the set_var created by the parser.

  @return @c FALSE if the change is allowed, otherwise @c TRUE.
*/
static bool check_sql_log_bin(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return TRUE;

  if (var->type == OPT_GLOBAL)
  {
    my_error(ER_INCORRECT_GLOBAL_LOCAL_VAR, MYF(0), self->name.str, "SESSION");
    return TRUE;
  }

  if (error_if_in_trans_or_substatement(thd,
          ER_STORED_FUNCTION_PREVENTS_SWITCH_SQL_LOG_BIN,
          ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_SQL_LOG_BIN))
    return TRUE;

  return FALSE;
}

static Sys_var_mybool Sys_log_binlog(
       "sql_log_bin", "Controls whether logging to the binary log is done",
       SESSION_VAR(sql_log_bin), NO_CMD_LINE, DEFAULT(TRUE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_sql_log_bin),
       ON_UPDATE(fix_sql_log_bin_after_update));

static Sys_var_bit Sys_sql_warnings(
       "sql_warnings", "sql_warnings",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_WARNINGS,
       DEFAULT(FALSE));

static Sys_var_bit Sys_sql_notes(
       "sql_notes", "sql_notes",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_SQL_NOTES,
       DEFAULT(TRUE));

static Sys_var_bit Sys_auto_is_null(
       "sql_auto_is_null", "sql_auto_is_null",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_AUTO_IS_NULL,
       DEFAULT(FALSE), NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_bit Sys_safe_updates(
       "sql_safe_updates", "sql_safe_updates",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_SAFE_UPDATES,
       DEFAULT(FALSE));

static Sys_var_bit Sys_buffer_results(
       "sql_buffer_result", "sql_buffer_result",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_BUFFER_RESULT,
       DEFAULT(FALSE));

static Sys_var_bit Sys_quote_show_create(
       "sql_quote_show_create", "sql_quote_show_create",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_QUOTE_SHOW_CREATE,
       DEFAULT(TRUE));

static Sys_var_bit Sys_foreign_key_checks(
       "foreign_key_checks", "foreign_key_checks",
       SESSION_VAR(option_bits), NO_CMD_LINE,
       REVERSE(OPTION_NO_FOREIGN_KEY_CHECKS),
       DEFAULT(TRUE), NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_bit Sys_unique_checks(
       "unique_checks", "unique_checks",
       SESSION_VAR(option_bits), NO_CMD_LINE,
       REVERSE(OPTION_RELAXED_UNIQUE_CHECKS),
       DEFAULT(TRUE), NO_MUTEX_GUARD, IN_BINLOG);

#ifdef ENABLED_PROFILING
static Sys_var_bit Sys_profiling(
       "profiling", "profiling",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_PROFILING,
       DEFAULT(FALSE));

static Sys_var_ulong Sys_profiling_history_size(
       "profiling_history_size", "Limit of query profiling memory",
       SESSION_VAR(profiling_history_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 100), DEFAULT(15), BLOCK_SIZE(1));
#endif

/*
  When this is set by a connection, binlogged events will be marked with a
  corresponding flag. The slave can be configured to not replicate events
  so marked.
  In the binlog dump thread on the master, this variable is re-used for a
  related purpose: The slave sets this flag when connecting to the master to
  request that the master filter out (ie. not send) any events with the flag
  set, thus saving network traffic on events that would be ignored by the
  slave anyway.
*/
static bool check_skip_replication(sys_var *self, THD *thd, set_var *var)
{
  /*
    We must not change @@skip_replication in the middle of a transaction or
    statement, as that could result in only part of the transaction / statement
    being replicated.
    (This would be particularly serious if we were to replicate eg.
    Rows_log_event without Table_map_log_event or transactional updates without
    the COMMIT).
  */
  if (error_if_in_trans_or_substatement(thd,
          ER_STORED_FUNCTION_PREVENTS_SWITCH_SKIP_REPLICATION,
          ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_SKIP_REPLICATION))
    return 1;

  return 0;
}

static Sys_var_bit Sys_skip_replication(
       "skip_replication", "skip_replication",
       SESSION_ONLY(option_bits), NO_CMD_LINE, OPTION_SKIP_REPLICATION,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_skip_replication));

static Sys_var_harows Sys_select_limit(
       "sql_select_limit",
       "The maximum number of rows to return from SELECT statements",
       SESSION_VAR(select_limit), NO_CMD_LINE,
       VALID_RANGE(0, HA_POS_ERROR), DEFAULT(HA_POS_ERROR), BLOCK_SIZE(1));

static bool update_timestamp(THD *thd, set_var *var)
{
  if (var->value)
  {
    my_hrtime_t hrtime = { hrtime_from_time(var->save_result.double_value) };
    thd->set_time(hrtime);
  }
  else // SET timestamp=DEFAULT
    thd->user_time.val= 0;
  return false;
}
static double read_timestamp(THD *thd)
{
  return thd->start_time +
         thd->start_time_sec_part/(double)TIME_SECOND_PART_FACTOR;
}
static Sys_var_session_special_double Sys_timestamp(
       "timestamp", "Set the time for this client",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, TIMESTAMP_MAX_VALUE),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0), 
       ON_UPDATE(update_timestamp), ON_READ(read_timestamp));

static bool update_last_insert_id(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->first_successful_insert_id_in_prev_stmt=
    var->save_result.ulonglong_value;
  return false;
}
static ulonglong read_last_insert_id(THD *thd)
{
  return (ulonglong) thd->read_first_successful_insert_id_in_prev_stmt();
}
static Sys_var_session_special Sys_last_insert_id(
       "last_insert_id", "The value to be returned from LAST_INSERT_ID()",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_last_insert_id), ON_READ(read_last_insert_id));

// alias for last_insert_id(), Sybase-style
static Sys_var_session_special Sys_identity(
       "identity", "Synonym for the last_insert_id variable",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_last_insert_id), ON_READ(read_last_insert_id));

/*
  insert_id should *not* be marked as written to the binlog (i.e., it
  should *not* be IN_BINLOG), because we want any statement that
  refers to insert_id explicitly to be unsafe.  (By "explicitly", we
  mean using @@session.insert_id, whereas insert_id is used
  "implicitly" when NULL value is inserted into an auto_increment
  column).

  We want statements referring explicitly to @@session.insert_id to be
  unsafe, because insert_id is modified internally by the slave sql
  thread when NULL values are inserted in an AUTO_INCREMENT column.
  This modification interfers with the value of the
  @@session.insert_id variable if @@session.insert_id is referred
  explicitly by an insert statement (as is seen by executing "SET
  @@session.insert_id=0; CREATE TABLE t (a INT, b INT KEY
  AUTO_INCREMENT); INSERT INTO t(a) VALUES (@@session.insert_id);" in
  statement-based logging mode: t will be different on master and
  slave).
*/
static bool update_insert_id(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->force_one_auto_inc_interval(var->save_result.ulonglong_value);
  return false;
}

static ulonglong read_insert_id(THD *thd)
{
  return thd->auto_inc_intervals_forced.minimum();
}
static Sys_var_session_special Sys_insert_id(
       "insert_id", "The value to be used by the following INSERT "
       "or ALTER TABLE statement when inserting an AUTO_INCREMENT value",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_insert_id), ON_READ(read_insert_id));

static bool update_rand_seed1(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->rand.seed1= (ulong) var->save_result.ulonglong_value;
  return false;
}
static ulonglong read_rand_seed(THD *thd)
{
  return 0;
}
static Sys_var_session_special Sys_rand_seed1(
       "rand_seed1", "Sets the internal state of the RAND() "
       "generator for replication purposes",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_rand_seed1), ON_READ(read_rand_seed));

static bool update_rand_seed2(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->rand.seed2= (ulong) var->save_result.ulonglong_value;
  return false;
}
static Sys_var_session_special Sys_rand_seed2(
       "rand_seed2", "Sets the internal state of the RAND() "
       "generator for replication purposes",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_rand_seed2), ON_READ(read_rand_seed));

static ulonglong read_error_count(THD *thd)
{
  return thd->warning_info->error_count();
}
// this really belongs to the SHOW STATUS
static Sys_var_session_special Sys_error_count(
       "error_count", "The number of errors that resulted from the "
       "last statement that generated messages",
       READ_ONLY sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), ON_READ(read_error_count));

static ulonglong read_warning_count(THD *thd)
{
  return thd->warning_info->warn_count();
}
// this really belongs to the SHOW STATUS
static Sys_var_session_special Sys_warning_count(
       "warning_count", "The number of errors, warnings, and notes "
       "that resulted from the last statement that generated messages",
       READ_ONLY sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), ON_READ(read_warning_count));

static Sys_var_ulong Sys_default_week_format(
       "default_week_format",
       "The default week format used by WEEK() functions",
       SESSION_VAR(default_week_format), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 7), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_group_concat_max_len(
       "group_concat_max_len",
       "The maximum length of the result of function  GROUP_CONCAT()",
       SESSION_VAR(group_concat_max_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, SIZE_T_MAX), DEFAULT(1024), BLOCK_SIZE(1));

static char *glob_hostname_ptr;
static Sys_var_charptr Sys_hostname(
       "hostname", "Server host name",
       READ_ONLY GLOBAL_VAR(glob_hostname_ptr), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(glob_hostname));

#ifndef EMBEDDED_LIBRARY
static Sys_var_charptr Sys_repl_report_host(
       "report_host",
       "Hostname or IP of the slave to be reported to the master during "
       "slave registration. Will appear in the output of SHOW SLAVE HOSTS. "
       "Leave unset if you do not want the slave to register itself with the "
       "master. Note that it is not sufficient for the master to simply read "
       "the IP of the slave off the socket once the slave connects. Due to "
       "NAT and other routing issues, that IP may not be valid for connecting "
       "to the slave from the master or other hosts",
       READ_ONLY GLOBAL_VAR(report_host), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_repl_report_user(
       "report_user",
       "The account user name of the slave to be reported to the master "
       "during slave registration",
       READ_ONLY GLOBAL_VAR(report_user), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_repl_report_password(
       "report_password",
       "The account password of the slave to be reported to the master "
       "during slave registration",
       READ_ONLY GLOBAL_VAR(report_password), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_uint Sys_repl_report_port(
       "report_port",
       "Port for connecting to slave reported to the master during slave "
       "registration. Set it only if the slave is listening on a non-default "
       "port or if you have a special tunnel from the master or other clients "
       "to the slave. If not sure, leave this option unset",
       READ_ONLY GLOBAL_VAR(report_port), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));
#endif

static Sys_var_mybool Sys_keep_files_on_create(
       "keep_files_on_create",
       "Don't overwrite stale .MYD and .MYI even if no directory is specified",
       SESSION_VAR(keep_files_on_create), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static char *license;
static Sys_var_charptr Sys_license(
       "license", "The type of license the server has",
       READ_ONLY GLOBAL_VAR(license), NO_CMD_LINE, IN_SYSTEM_CHARSET,
       DEFAULT(STRINGIFY_ARG(LICENSE)));

static bool check_log_path(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false; // DEFAULT is ok

  if (!var->save_result.string_value.str)
    return true;

  LEX_STRING *val= &var->save_result.string_value;

  if (val->length > FN_REFLEN)
  { // path is too long
    my_error(ER_PATH_LENGTH, MYF(0), self->name.str);
    return true;
  }

  char path[FN_REFLEN];
  size_t path_length= unpack_filename(path, val->str);

  if (!path_length)
    return true;

  static const LEX_CSTRING my_cnf= { STRING_WITH_LEN("my.cnf") };
  static const LEX_CSTRING my_ini= { STRING_WITH_LEN("my.ini") };
  if (path_length >= my_cnf.length)
  {
    if (strcasecmp(path + path_length - my_cnf.length, my_cnf.str) == 0)
      return true; // log file name ends with "my.cnf"
    DBUG_ASSERT(my_cnf.length == my_ini.length);
    if (strcasecmp(path + path_length - my_ini.length, my_ini.str) == 0)
      return true; // log file name ends with "my.ini"
  }

  MY_STAT f_stat;

  if (my_stat(path, &f_stat, MYF(0)))
  {
    if (!MY_S_ISREG(f_stat.st_mode) || !(f_stat.st_mode & MY_S_IWRITE))
      return true; // not a regular writable file
    return false;
  }

  (void) dirname_part(path, val->str, &path_length);

  if (val->length - path_length >= FN_LEN)
  { // filename is too long
      my_error(ER_PATH_LENGTH, MYF(0), self->name.str);
      return true;
  }

  if (!path_length) // no path is good path (remember, relative to datadir)
    return false;

  if (my_access(path, (F_OK|W_OK)))
    return true; // directory is not writable

  return false;
}
static bool fix_log(char** logname, const char* default_logname,
                    const char*ext, bool enabled, void (*reopen)(char*))
{
  if (!*logname) // SET ... = DEFAULT
  {
    make_default_log_name(logname, ext, false);
    if (!*logname)
      return true;
  }
  logger.lock_exclusive();
  mysql_mutex_unlock(&LOCK_global_system_variables);
  if (enabled)
    reopen(*logname);
  logger.unlock();
  mysql_mutex_lock(&LOCK_global_system_variables);
  return false;
}
static void reopen_general_log(char* name)
{
  logger.get_log_file_handler()->close(0);
  logger.get_log_file_handler()->open_query_log(name);
}
static bool fix_general_log_file(sys_var *self, THD *thd, enum_var_type type)
{
  return fix_log(&opt_logname,  opt_log_basename, ".log", opt_log,
                 reopen_general_log);
}
static Sys_var_charptr Sys_general_log_path(
       "general_log_file", "Log connections and queries to given file",
       PREALLOCATED GLOBAL_VAR(opt_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_log_path), ON_UPDATE(fix_general_log_file));

static void reopen_slow_log(char* name)
{
  logger.get_slow_log_file_handler()->close(0);
  logger.get_slow_log_file_handler()->open_slow_log(name);
}
static bool fix_slow_log_file(sys_var *self, THD *thd, enum_var_type type)
{
  return fix_log(&opt_slow_logname, opt_log_basename, "-slow.log",
                 opt_slow_log, reopen_slow_log);
}
static Sys_var_charptr Sys_slow_log_path(
       "slow_query_log_file", "Log slow queries to given log file. "
       "Defaults logging to 'hostname'-slow.log. Must be enabled to activate "
       "other slow log options",
       PREALLOCATED GLOBAL_VAR(opt_slow_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_log_path), ON_UPDATE(fix_slow_log_file));

/// @todo deprecate these four legacy have_PLUGIN variables and use I_S instead
export SHOW_COMP_OPTION have_csv, have_innodb= SHOW_OPTION_DISABLED;
export SHOW_COMP_OPTION have_ndbcluster, have_partitioning;
static Sys_var_have Sys_have_csv(
       "have_csv", "have_csv",
       READ_ONLY GLOBAL_VAR(have_csv), NO_CMD_LINE);

static Sys_var_have Sys_have_innodb(
       "have_innodb", "have_innodb",
       READ_ONLY GLOBAL_VAR(have_innodb), NO_CMD_LINE);

static Sys_var_have Sys_have_ndbcluster(
       "have_ndbcluster", "have_ndbcluster",
       READ_ONLY GLOBAL_VAR(have_ndbcluster), NO_CMD_LINE);

static Sys_var_have Sys_have_partition_db(
       "have_partitioning", "have_partitioning",
       READ_ONLY GLOBAL_VAR(have_partitioning), NO_CMD_LINE);

static Sys_var_have Sys_have_compress(
       "have_compress", "have_compress",
       READ_ONLY GLOBAL_VAR(have_compress), NO_CMD_LINE);

static Sys_var_have Sys_have_crypt(
       "have_crypt", "have_crypt",
       READ_ONLY GLOBAL_VAR(have_crypt), NO_CMD_LINE);

static Sys_var_have Sys_have_dlopen(
       "have_dynamic_loading", "have_dynamic_loading",
       READ_ONLY GLOBAL_VAR(have_dlopen), NO_CMD_LINE);

static Sys_var_have Sys_have_geometry(
       "have_geometry", "have_geometry",
       READ_ONLY GLOBAL_VAR(have_geometry), NO_CMD_LINE);

static Sys_var_have Sys_have_openssl(
       "have_openssl", "have_openssl",
       READ_ONLY GLOBAL_VAR(have_ssl), NO_CMD_LINE);

static Sys_var_have Sys_have_profiling(
       "have_profiling", "have_profiling",
       READ_ONLY GLOBAL_VAR(have_profiling), NO_CMD_LINE);

static Sys_var_have Sys_have_query_cache(
       "have_query_cache", "have_query_cache",
       READ_ONLY GLOBAL_VAR(have_query_cache), NO_CMD_LINE);

static Sys_var_have Sys_have_rtree_keys(
       "have_rtree_keys", "have_rtree_keys",
       READ_ONLY GLOBAL_VAR(have_rtree_keys), NO_CMD_LINE);

static Sys_var_have Sys_have_ssl(
       "have_ssl", "have_ssl",
       READ_ONLY GLOBAL_VAR(have_ssl), NO_CMD_LINE);

static Sys_var_have Sys_have_symlink(
       "have_symlink", "have_symlink",
       READ_ONLY GLOBAL_VAR(have_symlink), NO_CMD_LINE);

static bool fix_log_state(sys_var *self, THD *thd, enum_var_type type);
static Sys_var_mybool Sys_general_log(
       "general_log", "Log connections and queries to a table or log file. "
       "Defaults logging to a file 'hostname'.log or a table mysql.general_log"
       "if --log-output=TABLE is used",
       GLOBAL_VAR(opt_log), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state));

// Synonym of "general_log" for consistency with SHOW VARIABLES output
static Sys_var_mybool Sys_log(
       "log", "Alias for --general-log. Deprecated",
       GLOBAL_VAR(opt_log), NO_CMD_LINE,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state), DEPRECATED("'@@general_log'"));

static Sys_var_mybool Sys_slow_query_log(
       "slow_query_log",
       "Log slow queries to a table or log file. Defaults logging to a file "
       "'hostname'-slow.log or a table mysql.slow_log if --log-output=TABLE is "
       "used. Must be enabled to activate other slow log options",
       GLOBAL_VAR(opt_slow_log), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state));

/* Synonym of "slow_query_log" for consistency with SHOW VARIABLES output */
static Sys_var_mybool Sys_log_slow(
       "log_slow_queries",
       "Alias for --slow-query-log. Deprecated",
       GLOBAL_VAR(opt_slow_log), NO_CMD_LINE,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state), DEPRECATED("'@@slow_query_log'"));

static bool fix_log_state(sys_var *self, THD *thd, enum_var_type type)
{
  bool res;
  my_bool *UNINIT_VAR(newvalptr), newval, UNINIT_VAR(oldval);
  uint UNINIT_VAR(log_type);

  if (self == &Sys_general_log || self == &Sys_log)
  {
    newvalptr= &opt_log;
    oldval=    logger.get_log_file_handler()->is_open();
    log_type=  QUERY_LOG_GENERAL;
  }
  else if (self == &Sys_slow_query_log || self == &Sys_log_slow)
  {
    newvalptr= &opt_slow_log;
    oldval=    logger.get_slow_log_file_handler()->is_open();
    log_type=  QUERY_LOG_SLOW;
  }
  else
    DBUG_ASSERT(FALSE);

  newval= *newvalptr;
  if (oldval == newval)
    return false;

  *newvalptr= oldval; // [de]activate_log_handler works that way (sigh)

  mysql_mutex_unlock(&LOCK_global_system_variables);
  if (!newval)
  {
    logger.deactivate_log_handler(thd, log_type);
    res= false;
  }
  else
    res= logger.activate_log_handler(thd, log_type);
  mysql_mutex_lock(&LOCK_global_system_variables);
  return res;
}

static bool check_not_empty_set(sys_var *self, THD *thd, set_var *var)
{
  return var->save_result.ulonglong_value == 0;
}
static bool fix_log_output(sys_var *self, THD *thd, enum_var_type type)
{
  logger.lock_exclusive();
  logger.init_slow_log(log_output_options);
  logger.init_general_log(log_output_options);
  logger.unlock();
  return false;
}

static const char *log_output_names[] = { "NONE", "FILE", "TABLE", NULL};

static Sys_var_set Sys_log_output(
       "log_output", "Syntax: log-output=value[,value...], "
       "where \"value\" could be TABLE, FILE or NONE",
       GLOBAL_VAR(log_output_options), CMD_LINE(REQUIRED_ARG),
       log_output_names, DEFAULT(LOG_FILE), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_not_empty_set), ON_UPDATE(fix_log_output));

#ifdef HAVE_REPLICATION
static Sys_var_mybool Sys_log_slave_updates(
       "log_slave_updates", "Tells the slave to log the updates from "
       "the slave thread to the binary log. You will need to turn it on if "
       "you plan to daisy-chain the slaves",
       READ_ONLY GLOBAL_VAR(opt_log_slave_updates), CMD_LINE(OPT_ARG),
       DEFAULT(0));

static Sys_var_charptr Sys_relay_log(
       "relay_log", "The location and name to use for relay logs",
       READ_ONLY GLOBAL_VAR(opt_relay_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_relay_log_index(
       "relay_log_index", "The location and name to use for the file "
       "that keeps a list of the last relay logs",
       READ_ONLY GLOBAL_VAR(opt_relaylog_index_name), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_relay_log_info_file(
       "relay_log_info_file", "The location and name of the file that "
       "remembers where the SQL replication thread is in the relay logs",
       READ_ONLY GLOBAL_VAR(relay_log_info_file), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_relay_log_purge(
       "relay_log_purge", "if disabled - do not purge relay logs. "
       "if enabled - purge them as soon as they are no more needed",
       GLOBAL_VAR(relay_log_purge), CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_mybool Sys_relay_log_recovery(
       "relay_log_recovery", "Enables automatic relay log recovery "
       "right after the database startup, which means that the IO Thread "
       "starts re-fetching from the master right after the last transaction "
       "processed",
       GLOBAL_VAR(relay_log_recovery), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

bool Sys_var_rpl_filter::do_check(THD *thd, set_var *var)
{
  bool status;

  /*
    We must not be holding LOCK_global_system_variables here, otherwise we can
    deadlock with THD::init() which is invoked from within the slave threads
    with opposite locking order.
  */
  mysql_mutex_assert_not_owner(&LOCK_global_system_variables);

  mysql_mutex_lock(&LOCK_active_mi);
  mysql_mutex_lock(&active_mi->rli.run_lock);

  status= active_mi->rli.slave_running;

  mysql_mutex_unlock(&active_mi->rli.run_lock);
  mysql_mutex_unlock(&LOCK_active_mi);

  if (status)
    my_error(ER_SLAVE_MUST_STOP, MYF(0));
  else
    status= Sys_var_charptr::do_string_check(thd, var, charset(thd));

  return status;
}

void Sys_var_rpl_filter::lock(void)
{
  /*
    Starting a slave thread causes the new thread to attempt to
    acquire LOCK_global_system_variables (in THD::init) while
    LOCK_active_mi is being held by the thread that initiated
    the process. In order to not violate the lock order, unlock
    LOCK_global_system_variables before grabbing LOCK_active_mi.
  */
  mysql_mutex_unlock(&LOCK_global_system_variables);

  mysql_mutex_lock(&LOCK_active_mi);
  mysql_mutex_lock(&active_mi->rli.run_lock);
}

void Sys_var_rpl_filter::unlock(void)
{
  mysql_mutex_unlock(&active_mi->rli.run_lock);
  mysql_mutex_unlock(&LOCK_active_mi);

  mysql_mutex_lock(&LOCK_global_system_variables);
}

bool Sys_var_rpl_filter::global_update(THD *thd, set_var *var)
{
  bool slave_running, status= false;

  lock();

  if (! (slave_running= active_mi->rli.slave_running))
    status= set_filter_value(var->save_result.string_value.str);

  if (slave_running)
    my_error(ER_SLAVE_MUST_STOP, MYF(0));

  unlock();

  return slave_running || status;
}

bool Sys_var_rpl_filter::set_filter_value(const char *value)
{
  bool status= true;

  switch (opt_id) {
  case OPT_REPLICATE_DO_DB:
    status= rpl_filter->set_do_db(value);
    break;
  case OPT_REPLICATE_DO_TABLE:
    status= rpl_filter->set_do_table(value);
    break;
  case OPT_REPLICATE_IGNORE_DB:
    status= rpl_filter->set_ignore_db(value);
    break;
  case OPT_REPLICATE_IGNORE_TABLE:
    status= rpl_filter->set_ignore_table(value);
    break;
  case OPT_REPLICATE_WILD_DO_TABLE:
    status= rpl_filter->set_wild_do_table(value);
    break;
  case OPT_REPLICATE_WILD_IGNORE_TABLE:
    status= rpl_filter->set_wild_ignore_table(value);
    break;
  }

  return status;
}

uchar *Sys_var_rpl_filter::global_value_ptr(THD *thd, LEX_STRING *base)
{
  char buf[256];
  String tmp(buf, sizeof(buf), &my_charset_bin);

  tmp.length(0);

  lock();

  switch (opt_id) {
  case OPT_REPLICATE_DO_DB:
    rpl_filter->get_do_db(&tmp);
    break;
  case OPT_REPLICATE_DO_TABLE:
    rpl_filter->get_do_table(&tmp);
    break;
  case OPT_REPLICATE_IGNORE_DB:
    rpl_filter->get_ignore_db(&tmp);
    break;
  case OPT_REPLICATE_IGNORE_TABLE:
    rpl_filter->get_ignore_table(&tmp);
    break;
  case OPT_REPLICATE_WILD_DO_TABLE:
    rpl_filter->get_wild_do_table(&tmp);
    break;
  case OPT_REPLICATE_WILD_IGNORE_TABLE:
    rpl_filter->get_wild_ignore_table(&tmp);
    break;
  }

  unlock();

  return (uchar *) thd->strmake(tmp.ptr(), tmp.length());
}

static Sys_var_rpl_filter Sys_replicate_do_db(
       "replicate_do_db", OPT_REPLICATE_DO_DB,
       "Tell the slave to restrict replication to updates of tables "
       "whose names appear in the comma-separated list. For "
       "statement-based replication, only the default database (that "
       "is, the one selected by USE) is considered, not any explicitly "
       "mentioned tables in the query. For row-based replication, the "
       "actual names of table(s) being updated are checked.");

static Sys_var_rpl_filter Sys_replicate_do_table(
       "replicate_do_table", OPT_REPLICATE_DO_TABLE,
       "Tells the slave to restrict replication to tables in the "
       "comma-separated list.");

static Sys_var_rpl_filter Sys_replicate_ignore_db(
       "replicate_ignore_db", OPT_REPLICATE_IGNORE_DB,
       "Tell the slave to restrict replication to updates of tables "
       "whose names do not appear in the comma-separated list. For "
       "statement-based replication, only the default database (that "
       "is, the one selected by USE) is considered, not any explicitly "
       "mentioned tables in the query. For row-based replication, the "
       "actual names of table(s) being updated are checked.");

static Sys_var_rpl_filter Sys_replicate_ignore_table(
       "replicate_ignore_table", OPT_REPLICATE_IGNORE_TABLE,
       "Tells the slave thread not to replicate any statement that "
       "updates the specified table, even if any other tables might be "
       "updated by the same statement.");

static Sys_var_rpl_filter Sys_replicate_wild_do_table(
       "replicate_wild_do_table", OPT_REPLICATE_WILD_DO_TABLE,
       "Tells the slave thread to restrict replication to statements "
       "where any of the updated tables match the specified database "
       "and table name patterns.");

static Sys_var_rpl_filter Sys_replicate_wild_ignore_table(
       "replicate_wild_ignore_table", OPT_REPLICATE_WILD_IGNORE_TABLE,
       "Tells the slave thread to not replicate to the tables that "
       "match the given wildcard pattern.");

static Sys_var_charptr Sys_slave_load_tmpdir(
       "slave_load_tmpdir", "The location where the slave should put "
       "its temporary files when replicating a LOAD DATA INFILE command",
       READ_ONLY GLOBAL_VAR(slave_load_tmpdir), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static bool fix_slave_net_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  DEBUG_SYNC(thd, "fix_slave_net_timeout");

  mysql_mutex_unlock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_active_mi);
  DBUG_PRINT("info", ("slave_net_timeout=%u mi->heartbeat_period=%.3f",
                     slave_net_timeout,
                     (active_mi? active_mi->heartbeat_period : 0.0)));
  if (active_mi && slave_net_timeout < active_mi->heartbeat_period)
    push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                        ER_SLAVE_HEARTBEAT_VALUE_OUT_OF_RANGE_MAX,
                        ER(ER_SLAVE_HEARTBEAT_VALUE_OUT_OF_RANGE_MAX));
  mysql_mutex_unlock(&LOCK_active_mi);
  mysql_mutex_lock(&LOCK_global_system_variables);
  return false;
}
static Sys_var_uint Sys_slave_net_timeout(
       "slave_net_timeout", "Number of seconds to wait for more data "
       "from a master/slave connection before aborting the read",
       GLOBAL_VAR(slave_net_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(SLAVE_NET_TIMEOUT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_slave_net_timeout));

static bool check_slave_skip_counter(sys_var *self, THD *thd, set_var *var)
{
  bool result= false;
  mysql_mutex_lock(&LOCK_active_mi);
  mysql_mutex_lock(&active_mi->rli.run_lock);
  if (active_mi->rli.slave_running)
  {
    my_message(ER_SLAVE_MUST_STOP, ER(ER_SLAVE_MUST_STOP), MYF(0));
    result= true;
  }
  mysql_mutex_unlock(&active_mi->rli.run_lock);
  mysql_mutex_unlock(&LOCK_active_mi);
  return result;
}
static bool fix_slave_skip_counter(sys_var *self, THD *thd, enum_var_type type)
{
  mysql_mutex_unlock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_active_mi);
  mysql_mutex_lock(&active_mi->rli.run_lock);
  /*
    The following test should normally never be true as we test this
    in the check function;  To be safe against multiple
    SQL_SLAVE_SKIP_COUNTER request, we do the check anyway
  */
  if (!active_mi->rli.slave_running)
  {
    mysql_mutex_lock(&active_mi->rli.data_lock);
    active_mi->rli.slave_skip_counter= sql_slave_skip_counter;
    mysql_mutex_unlock(&active_mi->rli.data_lock);
  }
  mysql_mutex_unlock(&active_mi->rli.run_lock);
  mysql_mutex_unlock(&LOCK_active_mi);
  mysql_mutex_lock(&LOCK_global_system_variables);
  return 0;
}
static Sys_var_uint Sys_slave_skip_counter(
       "sql_slave_skip_counter", "sql_slave_skip_counter",
       GLOBAL_VAR(sql_slave_skip_counter), NO_CMD_LINE,
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_slave_skip_counter),
       ON_UPDATE(fix_slave_skip_counter));

static Sys_var_charptr Sys_slave_skip_errors(
       "slave_skip_errors", "Tells the slave thread to continue "
       "replication when a query event returns an error from the "
       "provided list",
       READ_ONLY GLOBAL_VAR(opt_slave_skip_errors), CMD_LINE(REQUIRED_ARG),
       IN_SYSTEM_CHARSET, DEFAULT(0));

static Sys_var_ulonglong Sys_relay_log_space_limit(
       "relay_log_space_limit", "Maximum space to use for all relay logs",
       READ_ONLY GLOBAL_VAR(relay_log_space_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONGLONG_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_relaylog_period(
       "sync_relay_log", "Synchronously flush relay log to disk after "
       "every #th event. Use 0 (default) to disable synchronous flushing",
       GLOBAL_VAR(sync_relaylog_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_relayloginfo_period(
       "sync_relay_log_info", "Synchronously flush relay log info "
       "to disk after every #th transaction. Use 0 (default) to disable "
       "synchronous flushing",
       GLOBAL_VAR(sync_relayloginfo_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));
#endif

static Sys_var_uint Sys_sync_binlog_period(
       "sync_binlog", "Synchronously flush binary log to disk after "
       "every #th event. Use 0 (default) to disable synchronous flushing",
       GLOBAL_VAR(sync_binlog_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_masterinfo_period(
       "sync_master_info", "Synchronously flush master info to disk "
       "after every #th event. Use 0 (default) to disable synchronous flushing",
       GLOBAL_VAR(sync_masterinfo_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

#ifdef HAVE_REPLICATION
static Sys_var_ulong Sys_slave_trans_retries(
       "slave_transaction_retries", "Number of times the slave SQL "
       "thread will retry a transaction in case it failed with a deadlock "
       "or elapsed lock wait timeout, before giving up and stopping",
       GLOBAL_VAR(slave_trans_retries), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(10), BLOCK_SIZE(1));
#endif

static bool check_locale(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  MY_LOCALE *locale;
  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == INT_RESULT)
  {
    int lcno= (int)var->value->val_int();
    if (!(locale= my_locale_by_number(lcno)))
    {
      my_error(ER_UNKNOWN_LOCALE, MYF(0), llstr(lcno, buff));
      return true;
    }
    if (check_not_null(self, thd, var))
      return true;
  }
  else // STRING_RESULT
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res=var->value->val_str(&str)))
      return true;
    else if (!(locale= my_locale_by_name(res->c_ptr_safe())))
    {
      ErrConvString err(res);
      my_error(ER_UNKNOWN_LOCALE, MYF(0), err.ptr());
      return true;
    }
  }

  var->save_result.ptr= locale;

  if (!locale->errmsgs->errmsgs)
  {
    bool res;
    mysql_mutex_lock(&LOCK_error_messages);
    res= (!locale->errmsgs->errmsgs &&
          read_texts(ERRMSG_FILE, locale->errmsgs->language,
                     &locale->errmsgs->errmsgs,
                     ER_ERROR_LAST - ER_ERROR_FIRST + 1));
    mysql_mutex_unlock(&LOCK_error_messages);
    if (res)
    {
      push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
                          "Can't process error message file for locale '%s'",
                          locale->name);
      return true;
    }
  }
  status_var_increment(thd->status_var.feature_locale);
  return false;
}

static Sys_var_struct Sys_lc_messages(
       "lc_messages", "Set the language used for the error messages",
       SESSION_VAR(lc_messages), NO_CMD_LINE,
       my_offsetof(MY_LOCALE, name), DEFAULT(&my_default_lc_messages),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_locale));

static Sys_var_struct Sys_lc_time_names(
       "lc_time_names", "Set the language used for the month "
       "names and the days of the week",
       SESSION_VAR(lc_time_names), NO_CMD_LINE,
       my_offsetof(MY_LOCALE, name), DEFAULT(&my_default_lc_time_names),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_locale));

static Sys_var_tz Sys_time_zone(
       "time_zone", "time_zone",
       SESSION_VAR(time_zone), NO_CMD_LINE,
       DEFAULT(&default_tz), NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_charptr Sys_ignore_db_dirs(
       "ignore_db_dirs",
       "Specifies a directory to add to the ignore list when collecting "
       "database names from the datadir. Put a blank argument to reset "
       "the list accumulated so far.",
       READ_ONLY GLOBAL_VAR(opt_ignore_db_dirs), 
       CMD_LINE(REQUIRED_ARG, OPT_IGNORE_DB_DIRECTORY),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_ulong Sys_sp_cache_size(
       "stored_program_cache",
       "The soft upper limit for number of cached stored routines for "
       "one connection.",
       GLOBAL_VAR(stored_program_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 512 * 1024), DEFAULT(256), BLOCK_SIZE(1));

export const char *plugin_maturity_names[]=
{ "unknown", "experimental", "alpha", "beta", "gamma", "stable", 0 };
static Sys_var_enum Sys_plugin_maturity(
       "plugin_maturity",
       "The lowest desirable plugin maturity "
       "(unknown, experimental, alpha, beta, gamma, or stable). "
       "Plugins less mature than that will not be installed or loaded.",
       READ_ONLY GLOBAL_VAR(plugin_maturity), CMD_LINE(REQUIRED_ARG),
       plugin_maturity_names, DEFAULT(MariaDB_PLUGIN_MATURITY_UNKNOWN));

static Sys_var_ulong Sys_deadlock_search_depth_short(
       "deadlock_search_depth_short",
       "Short search depth for the two-step deadlock detection",
       SESSION_VAR(wt_deadlock_search_depth_short), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 32), DEFAULT(4), BLOCK_SIZE(1));

static Sys_var_ulong Sys_deadlock_search_depth_long(
       "deadlock_search_depth_long",
       "Long search depth for the two-step deadlock detection",
       SESSION_VAR(wt_deadlock_search_depth_long), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 33), DEFAULT(15), BLOCK_SIZE(1));

static Sys_var_ulong Sys_deadlock_timeout_depth_short(
       "deadlock_timeout_short",
       "Short timeout for the two-step deadlock detection (in microseconds)",
       SESSION_VAR(wt_timeout_short), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(10000), BLOCK_SIZE(1));

static Sys_var_ulong Sys_deadlock_timeout_depth_long(
       "deadlock_timeout_long",
       "Long timeout for the two-step deadlock detection (in microseconds)",
       SESSION_VAR(wt_timeout_long), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(50000000), BLOCK_SIZE(1));

#ifndef DBUG_OFF
static Sys_var_ulong Sys_debug_crc_break(
       "debug_crc_break",
       "Call my_debug_put_break_here() if crc matches this number (for debug)",
       GLOBAL_VAR(my_crc_dbug_check), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1));
#endif

static Sys_var_uint Sys_extra_port(
       "extra_port",
       "Extra port number to use for tcp connections in a "
       "one-thread-per-connection manner. 0 means don't use another port",
       READ_ONLY GLOBAL_VAR(mysqld_extra_port), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulong Sys_extra_max_connections(
       "extra_max_connections", "The number of connections on extra-port",
       GLOBAL_VAR(extra_max_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 100000), DEFAULT(1), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_max_connections));

#ifdef SAFE_MUTEX
static Sys_var_mybool Sys_mutex_deadlock_detector(
       "mutex_deadlock_detector", "Enable checking of wrong mutex usage",
       READ_ONLY GLOBAL_VAR(safe_mutex_deadlock_detector),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE));
#endif

static Sys_var_keycache Sys_key_cache_segments(
       "key_cache_segments", "The number of segments in a key cache",
       KEYCACHE_VAR(param_partitions),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_PARTITIONS),
       VALID_RANGE(0, MAX_KEY_CACHE_PARTITIONS),
       DEFAULT(DEFAULT_KEY_CACHE_PARTITIONS),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(repartition_keycache));

static const char *log_slow_filter_names[]= 
{ "admin", "filesort", "filesort_on_disk", "full_join", "full_scan",
  "query_cache", "query_cache_miss", "tmp_table", "tmp_table_on_disk", 0
};
static Sys_var_set Sys_log_slow_filter(
       "log_slow_filter",
       "Log only certain types of queries. Multiple "
       "flags can be specified, separated by commas. Valid values are admin, "
       "slave, filesort, filesort_on_disk, full_join, full_scan, query_cache, "
       "query_cache_miss, tmp_table, tmp_table_on_disk",
       SESSION_VAR(log_slow_filter), CMD_LINE(REQUIRED_ARG),
       log_slow_filter_names,
       DEFAULT(MAX_SET(array_elements(log_slow_filter_names)-1)));

static Sys_var_ulong Sys_log_slow_rate_limit(
       "log_slow_rate_limit",
       "Write to slow log every #th slow query. Set to 1 to log everything. "
       "Increase it to reduce the size of the slow or the performance impact "
       "of slow logging",
       SESSION_VAR(log_slow_rate_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, UINT_MAX), DEFAULT(1), BLOCK_SIZE(1));

static const char *log_slow_verbosity_names[]= { "innodb", "query_plan", 0 };
static Sys_var_set Sys_log_slow_verbosity(
       "log_slow_verbosity",
       "log-slow-verbosity=[value[,value ...]] where value is one of "
       "'innodb', 'query_plan'",
       SESSION_VAR(log_slow_verbosity), CMD_LINE(REQUIRED_ARG),
       log_slow_verbosity_names, DEFAULT(LOG_SLOW_VERBOSITY_INIT));

static Sys_var_ulong Sys_join_cache_level(
       "join_cache_level",
       "Controls what join operations can be executed with join buffers. Odd "
       "numbers are used for plain join buffers while even numbers are used "
       "for linked buffers",
       SESSION_VAR(join_cache_level), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 8), DEFAULT(2), BLOCK_SIZE(1));

static Sys_var_ulong Sys_mrr_buffer_size(
       "mrr_buffer_size",
       "Size of buffer to use when using MRR with range access",
       SESSION_VAR(mrr_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE*2, INT_MAX32), DEFAULT(256*1024), BLOCK_SIZE(1));

static Sys_var_ulong Sys_rowid_merge_buff_size(
       "rowid_merge_buff_size",
       "The size of the buffers used [NOT] IN evaluation via partial matching",
       SESSION_VAR(rowid_merge_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ((ulonglong)~(intptr)0)/2), DEFAULT(8*1024*1024),
       BLOCK_SIZE(1));

static Sys_var_mybool Sys_userstat(
       "userstat",
       "Enables statistics gathering for USER_STATISTICS, CLIENT_STATISTICS, "
       "INDEX_STATISTICS and TABLE_STATISTICS tables in the INFORMATION_SCHEMA",
       GLOBAL_VAR(opt_userstat_running),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_binlog_annotate_row_events(
       "binlog_annotate_row_events",
       "Tells the master to annotate RBR events with the statement that "
       "caused these events",
       SESSION_VAR(binlog_annotate_row_events), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

#ifdef HAVE_REPLICATION
static Sys_var_mybool Sys_replicate_annotate_row_events(
       "replicate_annotate_row_events",
       "Tells the slave to write annotate rows events recieved from the master "
       "to its own binary log. Ignored if log_slave_updates is not set",
       READ_ONLY GLOBAL_VAR(opt_replicate_annotate_row_events),
       CMD_LINE(OPT_ARG), DEFAULT(0));
#endif

static Sys_var_ulonglong Sys_join_buffer_space_limit(
       "join_buffer_space_limit",
       "The limit of the space for all join buffers used by a query",
       SESSION_VAR(join_buff_space_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(2048, ULONGLONG_MAX), DEFAULT(16*128*1024),
       BLOCK_SIZE(2048));

static Sys_var_ulong Sys_progress_report_time(
       "progress_report_time",
       "Seconds between sending progress reports to the client for "
       "time-consuming statements. Set to 0 to disable progress reporting.",
       SESSION_VAR(progress_report_time), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(5), BLOCK_SIZE(1));

static Sys_var_mybool Sys_no_thread_alarm(
       "debug_no_thread_alarm",
       "Disable system thread alarm calls. Disabling it may be useful "
       "in debugging or testing, never do it in production",
       READ_ONLY GLOBAL_VAR(my_disable_thr_alarm), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_mybool Sys_query_cache_strip_comments(
       "query_cache_strip_comments",
       "Strip all comments from a query before storing it "
       "in the query cache",
       SESSION_VAR(query_cache_strip_comments), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static ulonglong in_transaction(THD *thd)
{
  return test(thd->in_active_multi_stmt_transaction());
}
static Sys_var_session_special Sys_in_transaction(
       "in_transaction", "Whether there is an active transaction",
       READ_ONLY sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, 1), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), ON_READ(in_transaction));

#ifndef DBUG_OFF
static Sys_var_ulong Sys_debug_binlog_fsync_sleep(
       "debug_binlog_fsync_sleep",
       "Extra sleep (in microseconds) to add to binlog fsync(), for debugging",
       GLOBAL_VAR(opt_binlog_dbug_fsync_sleep),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));
#endif

static Sys_var_harows Sys_expensive_subquery_limit(
       "expensive_subquery_limit",
       "The maximum number of rows a subquery may examine in order to be "
       "executed during optimization and used for constant optimization",
       SESSION_VAR(expensive_subquery_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, HA_POS_ERROR), DEFAULT(100), BLOCK_SIZE(1));

static bool check_pseudo_slave_mode(sys_var *self, THD *thd, set_var *var)
{
  longlong previous_val= thd->variables.pseudo_slave_mode;
  longlong val= (longlong) var->save_result.ulonglong_value;
  bool rli_fake= false;

#ifndef EMBEDDED_LIBRARY
  rli_fake= thd->rli_fake ? true : false;
#endif

  if (rli_fake)
  {
    if (!val)
    {
#ifndef EMBEDDED_LIBRARY
      delete thd->rli_fake;
      thd->rli_fake= NULL;
#endif
    }
    else if (previous_val && val)
      goto ineffective;
    else if (!previous_val && val)
      push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                   ER_WRONG_VALUE_FOR_VAR,
                   "'pseudo_slave_mode' is already ON.");
  }
  else
  {
    if (!previous_val && !val)
      goto ineffective;
    else if (previous_val && !val)
      push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
                   ER_WRONG_VALUE_FOR_VAR,
                   "Slave applier execution mode not active, "
                   "statement ineffective.");
  }
  goto end;

ineffective:
  push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
               ER_WRONG_VALUE_FOR_VAR,
               "'pseudo_slave_mode' change was ineffective.");

end:
  return FALSE;
}
static Sys_var_mybool Sys_pseudo_slave_mode(
       "pseudo_slave_mode",
       "SET pseudo_slave_mode= 0,1 are commands that mysqlbinlog "
       "adds to beginning and end of binary log dumps. While zero "
       "value indeed disables, the actual enabling of the slave "
       "applier execution mode is done implicitly when a "
       "Format_description_event is sent through the session.",
       SESSION_ONLY(pseudo_slave_mode), NO_CMD_LINE, DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_pseudo_slave_mode));