~ubuntu-branches/ubuntu/trusty/drizzle/trusty

/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
 *  vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
 *
 *  Copyright (C) 2008 Sun Microsystems, Inc.
 *
 *  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  02110-1301  USA
 */

/**
  @file Handling of MySQL SQL variables

  @details
  To add a new variable, one has to do the following:

  - Use one of the 'sys_var... classes from set_var.h or write a specific
    one for the variable type.
  - Define it in the 'variable definition list' in this file.
  - If the variable is thread specific, add it to 'system_variables' struct.
    If not, add it to mysqld.cc and an declaration in 'mysql_priv.h'
  - If the variable should be changed from the command line, add a definition
    of it in the option structure list in mysqld.cc
  - Don't forget to initialize new fields in global_system_variables and
    max_system_variables!

  @todo
    Add full support for the variable character_set (for 4.1)

*/

#include <config.h>
#include <drizzled/option.h>
#include <drizzled/error.h>
#include <drizzled/gettext.h>
#include <drizzled/data_home.h>
#include <drizzled/set_var.h>
#include <drizzled/session.h>
#include <drizzled/session/times.h>
#include <drizzled/sql_base.h>
#include <drizzled/lock.h>
#include <drizzled/item/uint.h>
#include <drizzled/item/null.h>
#include <drizzled/item/float.h>
#include <drizzled/item/string.h>
#include <drizzled/plugin.h>
#include <drizzled/version.h>
#include <drizzled/internal/m_string.h>
#include <drizzled/pthread_globals.h>
#include <drizzled/charset.h>
#include <drizzled/transaction_services.h>
#include <drizzled/constrained_value.h>
#include <drizzled/visibility.h>
#include <drizzled/typelib.h>
#include <drizzled/plugin/storage_engine.h>
#include <drizzled/system_variables.h>
#include <drizzled/catalog/instance.h>

#include <cstdio>
#include <map>
#include <vector>
#include <algorithm>

using namespace std;

namespace drizzled {

namespace internal
{
	extern bool timed_mutexes;
}

extern plugin::StorageEngine *myisam_engine;
extern bool timed_mutexes;

extern struct option my_long_options[];
extern const charset_info_st *character_set_filesystem;
extern size_t my_thread_stack_size;

typedef map<string, sys_var *> SystemVariableMap;
static SystemVariableMap system_variable_map;
extern char *opt_drizzle_tmpdir;

extern TYPELIB tx_isolation_typelib;

namespace
{
  static size_t revno= DRIZZLE_VC_REVNO;
  static size_t release_id= DRIZZLE_RELEASE_ID;
}

const char *bool_type_names[]= { "OFF", "ON", NULL };
TYPELIB bool_typelib=
{
  array_elements(bool_type_names)-1, "", bool_type_names, NULL
};

static bool set_option_bit(Session*, set_var*);
static bool set_option_autocommit(Session*, set_var*);
static int  check_pseudo_thread_id(Session*, set_var*);
static int check_tx_isolation(Session*, set_var*);
static void fix_tx_isolation(Session*, sql_var_t);
static int check_completion_type(Session*, set_var*);
static void fix_max_join_size(Session*, sql_var_t);
static void fix_session_mem_root(Session*, sql_var_t);
void throw_bounds_warning(Session*, bool fixed, bool unsignd, const std::string &name, int64_t);
static unsigned char *get_error_count(Session*);
static unsigned char *get_warning_count(Session*);
static unsigned char *get_tmpdir(Session*);

/*
  Variable definition list

  These are variables that can be set from the command line, in
  alphabetic order.

  The variables are linked into the list. A variable is added to
  it in the constructor (see sys_var class for details).
*/
static sys_var_session_uint64_t
sys_auto_increment_increment("auto_increment_increment", &drizzle_system_variables::auto_increment_increment);
static sys_var_session_uint64_t
sys_auto_increment_offset("auto_increment_offset", &drizzle_system_variables::auto_increment_offset);

static sys_var_fs_path sys_basedir("basedir", basedir);
static sys_var_fs_path sys_pid_file("pid_file", pid_file);
static sys_var_fs_path sys_plugin_dir("plugin_dir", plugin_dir);

static sys_var_size_t_ptr sys_thread_stack_size("thread_stack", &my_thread_stack_size);
static sys_var_constrained_value_readonly<uint32_t> sys_back_log("back_log", back_log);

static sys_var_session_uint64_t	sys_bulk_insert_buff_size("bulk_insert_buffer_size", &drizzle_system_variables::bulk_insert_buff_size);
static sys_var_session_uint32_t	sys_completion_type("completion_type", &drizzle_system_variables::completion_type, check_completion_type);
static sys_var_collation_sv
sys_collation_server("collation_server", &drizzle_system_variables::collation_server, &default_charset_info);
static sys_var_fs_path sys_datadir("datadir", getDataHome());

static sys_var_session_uint64_t	sys_join_buffer_size("join_buffer_size", &drizzle_system_variables::join_buff_size);
static sys_var_session_uint32_t	sys_max_allowed_packet("max_allowed_packet", &drizzle_system_variables::max_allowed_packet);
static sys_var_session_uint64_t	sys_max_error_count("max_error_count", &drizzle_system_variables::max_error_count);
static sys_var_session_uint64_t	sys_max_heap_table_size("max_heap_table_size", &drizzle_system_variables::max_heap_table_size);
static sys_var_session_uint64_t sys_pseudo_thread_id("pseudo_thread_id", &drizzle_system_variables::pseudo_thread_id, 0, check_pseudo_thread_id);
static sys_var_session_ha_rows	sys_max_join_size("max_join_size", &drizzle_system_variables::max_join_size, fix_max_join_size);
static sys_var_session_uint64_t	sys_max_seeks_for_key("max_seeks_for_key", &drizzle_system_variables::max_seeks_for_key);
static sys_var_session_uint64_t sys_max_length_for_sort_data("max_length_for_sort_data", &drizzle_system_variables::max_length_for_sort_data);
static sys_var_session_size_t	sys_max_sort_length("max_sort_length", &drizzle_system_variables::max_sort_length);
static sys_var_uint64_t_ptr	sys_max_write_lock_count("max_write_lock_count", &max_write_lock_count);
static sys_var_session_uint64_t sys_min_examined_row_limit("min_examined_row_limit", &drizzle_system_variables::min_examined_row_limit);

static sys_var_session_bool sys_optimizer_prune_level("optimizer_prune_level", &drizzle_system_variables::optimizer_prune_level);
static sys_var_session_uint32_t sys_optimizer_search_depth("optimizer_search_depth", &drizzle_system_variables::optimizer_search_depth);

static sys_var_session_uint64_t sys_preload_buff_size("preload_buffer_size", &drizzle_system_variables::preload_buff_size);
static sys_var_session_uint32_t sys_read_buff_size("read_buffer_size", &drizzle_system_variables::read_buff_size);
static sys_var_session_uint32_t	sys_read_rnd_buff_size("read_rnd_buffer_size", &drizzle_system_variables::read_rnd_buff_size);
static sys_var_session_uint32_t	sys_div_precincrement("div_precision_increment", &drizzle_system_variables::div_precincrement);

static sys_var_session_size_t	sys_range_alloc_block_size("range_alloc_block_size", &drizzle_system_variables::range_alloc_block_size);

static sys_var_session_bool sys_replicate_query("replicate_query", &drizzle_system_variables::replicate_query);

static sys_var_session_uint32_t	sys_query_alloc_block_size("query_alloc_block_size", &drizzle_system_variables::query_alloc_block_size, NULL, fix_session_mem_root);
static sys_var_session_uint32_t	sys_query_prealloc_size("query_prealloc_size", &drizzle_system_variables::query_prealloc_size, NULL, fix_session_mem_root);
static sys_var_readonly sys_tmpdir("tmpdir", OPT_GLOBAL, SHOW_CHAR, get_tmpdir);

static sys_var_fs_path sys_secure_file_priv("secure_file_priv", secure_file_priv);
static sys_var_const_str_ptr sys_scheduler("scheduler", (char**)&opt_scheduler);

static sys_var_uint32_t_ptr  sys_server_id("server_id", &server_id);

static sys_var_const_string sys_server_uuid("server_uuid", server_uuid);

static sys_var_session_size_t	sys_sort_buffer("sort_buffer_size", &drizzle_system_variables::sortbuff_size);

static sys_var_size_t_ptr_readonly sys_transaction_message_threshold("transaction_message_threshold", &transaction_message_threshold);

static sys_var_session_storage_engine sys_storage_engine("storage_engine", &drizzle_system_variables::storage_engine);
static sys_var_size_t_ptr	sys_table_def_size("table_definition_cache", &table_def_size);
static sys_var_uint64_t_ptr	sys_table_cache_size("table_open_cache", &table_cache_size);
static sys_var_uint64_t_ptr	sys_table_lock_wait_timeout("table_lock_wait_timeout", &table_lock_wait_timeout);
static sys_var_session_enum	sys_tx_isolation("tx_isolation",
                                             &drizzle_system_variables::tx_isolation,
                                             &tx_isolation_typelib,
                                             fix_tx_isolation,
                                             check_tx_isolation);
static sys_var_session_uint64_t	sys_tmp_table_size("tmp_table_size",
					   &drizzle_system_variables::tmp_table_size);
static sys_var_bool_ptr  sys_timed_mutexes("timed_mutexes", &internal::timed_mutexes);
static sys_var_const_str  sys_version("version", version().c_str());

static sys_var_const_str sys_version_comment("version_comment", COMPILATION_COMMENT);
static sys_var_const_str sys_version_compile_machine("version_compile_machine", HOST_CPU);
static sys_var_const_str sys_version_compile_os("version_compile_os", HOST_OS);
static sys_var_const_str sys_version_compile_vendor("version_compile_vendor", HOST_VENDOR);

/* Variables that are bits in Session */

sys_var_session_bit sys_autocommit("autocommit", 0, set_option_autocommit, OPTION_NOT_AUTOCOMMIT, 1);
static sys_var_session_bit sys_big_selects("sql_big_selects", 0, set_option_bit, OPTION_BIG_SELECTS);
static sys_var_session_bit sys_sql_warnings("sql_warnings", 0, set_option_bit, OPTION_WARNINGS);
static sys_var_session_bit sys_sql_notes("sql_notes", 0, set_option_bit, OPTION_SQL_NOTES);
static sys_var_session_bit sys_buffer_results("sql_buffer_result", 0, set_option_bit, OPTION_BUFFER_RESULT);
static sys_var_session_bit sys_foreign_key_checks("foreign_key_checks", 0, set_option_bit, OPTION_NO_FOREIGN_KEY_CHECKS, 1);
static sys_var_session_bit sys_unique_checks("unique_checks", 0, set_option_bit, OPTION_RELAXED_UNIQUE_CHECKS, 1);
/* Local state variables */

static sys_var_session_ha_rows	sys_select_limit("sql_select_limit", &drizzle_system_variables::select_limit);
static sys_var_timestamp sys_timestamp("timestamp");
static sys_var_last_insert_id
sys_last_insert_id("last_insert_id");
/*
  identity is an alias for last_insert_id(), so that we are compatible
  with Sybase
*/
static sys_var_last_insert_id sys_identity("identity");

static sys_var_session_lc_time_names sys_lc_time_names("lc_time_names");

/*
  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 sys_var_readonly sys_error_count("error_count", OPT_SESSION, SHOW_INT, get_error_count);
static sys_var_readonly sys_warning_count("warning_count", OPT_SESSION, SHOW_INT, get_warning_count);

sys_var_session_uint64_t sys_group_concat_max_len("group_concat_max_len", &drizzle_system_variables::group_concat_max_len);

/* Global read-only variable containing hostname */
static sys_var_const_string sys_hostname("hostname", getServerHostname());

static sys_var_const_str sys_revid("vc_revid", DRIZZLE_VC_REVID);
static sys_var_const_str sys_branch("vc_branch", DRIZZLE_VC_BRANCH);
static sys_var_size_t_ptr_readonly sys_revno("vc_revno", &revno);
static sys_var_size_t_ptr_readonly sys_release_id("vc_release_id", &release_id);

bool sys_var::check(Session *session, set_var *var)
{
  if (check_func)
  {
    int res= (*check_func)(session, var);
    if (res < 0)
      my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), getName().c_str(), var->value->str_value.ptr());
    return res;
  }
  var->updateValue();
  return 0;
}

bool sys_var_str::check(Session *session, set_var *var)
{
  if (not check_func)
    return 0;

  int res= (*check_func)(session, var);
  if (res < 0)
    my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), getName().c_str(), var->value->str_value.ptr());
  return res;
}

bool sys_var_std_string::check(Session *session, set_var *var)
{
  if (not check_func)
    return false;

  if ((*check_func)(session, var))
  {
    my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), getName().c_str(), var->value->str_value.ptr());
    return true;
  }
  return false;
}

/*
  Functions to check and update variables
*/


/**
  Set the OPTION_BIG_SELECTS flag if max_join_size == HA_POS_ERROR.
*/

static void fix_max_join_size(Session *session, sql_var_t type)
{
  if (type != OPT_GLOBAL)
  {
    if (session->variables.max_join_size == HA_POS_ERROR)
      session->options|= OPTION_BIG_SELECTS;
    else
      session->options&= ~OPTION_BIG_SELECTS;
  }
}


/**
  Can't change the 'next' tx_isolation while we are already in
  a transaction
*/
static int check_tx_isolation(Session *session, set_var *var)
{
  if (var->type == OPT_DEFAULT && (session->server_status & SERVER_STATUS_IN_TRANS))
  {
    my_error(ER_CANT_CHANGE_TX_ISOLATION, MYF(0));
    return 1;
  }
  return 0;
}

/*
  If one doesn't use the SESSION modifier, the isolation level
  is only active for the next command.
*/
static void fix_tx_isolation(Session *session, sql_var_t type)
{
  if (type == OPT_SESSION)
    session->session_tx_isolation= (enum_tx_isolation) session->variables.tx_isolation;
}

static int check_completion_type(Session *, set_var *var)
{
  int64_t val= var->value->val_int();
  if (val < 0 || val > 2)
  {
    char buf[64];
    my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), var->var->getName().c_str(), internal::llstr(val, buf));
    return 1;
  }
  return 0;
}


static void fix_session_mem_root(Session *session, sql_var_t type)
{
  if (type != OPT_GLOBAL)
    session->mem.reset_defaults(session->variables.query_alloc_block_size, session->variables.query_prealloc_size);
}


void throw_bounds_warning(Session *session, bool fixed, bool unsignd, const std::string &name, int64_t val)
{
  if (not fixed)
    return;
  char buf[DECIMAL_LONGLONG_DIGITS];

  if (unsignd)
    internal::ullstr((uint64_t) val, buf);
  else
    internal::llstr(val, buf);

  push_warning_printf(session, DRIZZLE_ERROR::WARN_LEVEL_ERROR,
    ER_TRUNCATED_WRONG_VALUE, ER(ER_TRUNCATED_WRONG_VALUE), name.c_str(), buf);
}

uint64_t fix_unsigned(Session *session, uint64_t num, const option& option_limits)
{
  bool fixed= false;
  uint64_t out= getopt_ull_limit_value(num, option_limits, &fixed);

  throw_bounds_warning(session, fixed, true, option_limits.name, (int64_t) num);
  return out;
}


static size_t fix_size_t(Session *session, size_t num, const option& option_limits)
{
  bool fixed= false;
  size_t out= (size_t)getopt_ull_limit_value(num, option_limits, &fixed);

  throw_bounds_warning(session, fixed, true, option_limits.name, (int64_t) num);
  return out;
}

bool sys_var_uint32_t_ptr::check(Session *, set_var *var)
{
  var->updateValue();
  return 0;
}

bool sys_var_uint32_t_ptr::update(Session *session, set_var *var)
{
  uint64_t tmp= var->getInteger();
  boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());

  if (option_limits)
  {
    uint32_t newvalue= (uint32_t) fix_unsigned(session, tmp, *option_limits);
    if (static_cast<uint64_t>(newvalue) == tmp)
      *value= newvalue;
  }
  else
  {
    *value= static_cast<uint32_t>(tmp);
  }

  return 0;
}


void sys_var_uint32_t_ptr::set_default(Session *session, sql_var_t)
{
  bool not_used;
  boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
  *value= (uint32_t)getopt_ull_limit_value((uint32_t) option_limits->def_value, *option_limits, &not_used);
}


bool sys_var_uint64_t_ptr::update(Session *session, set_var *var)
{
  uint64_t tmp= var->getInteger();
  boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());

  if (option_limits)
  {
    uint64_t newvalue= fix_unsigned(session, tmp, *option_limits);
    if (newvalue==tmp)
      *value= newvalue;
  }
  else
  {
    *value= tmp;
  }

  return 0;
}


void sys_var_uint64_t_ptr::set_default(Session *session, sql_var_t)
{
  if (have_default_value)
  {
    *value= default_value;
  }
  else
  {
    bool not_used;
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    *value= getopt_ull_limit_value((uint64_t) option_limits->def_value, *option_limits, &not_used);
  }
}


bool sys_var_size_t_ptr::update(Session *session, set_var *var)
{
  size_t tmp= size_t(var->getInteger());

  boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());

  if (option_limits)
    *value= fix_size_t(session, tmp, *option_limits);
  else
    *value= tmp;

  return 0;
}


void sys_var_size_t_ptr::set_default(Session *session, sql_var_t)
{
  bool not_used;
  boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
  *value= (size_t)getopt_ull_limit_value((size_t) option_limits->def_value, *option_limits, &not_used);
}

bool sys_var_bool_ptr::check(Session *session, set_var *var)
{
  return check_enum(session, var, &bool_typelib);
}

bool sys_var_bool_ptr::update(Session *, set_var *var)
{
  *value= bool(var->getInteger());
  return 0;
}


void sys_var_bool_ptr::set_default(Session *, sql_var_t)
{
  *value= default_value;
}


/*
  32 bit types for session variables
*/
bool sys_var_session_uint32_t::check(Session *session, set_var *var)
{
  var->updateValue();
  return (check_func && (*check_func)(session, var));
}

bool sys_var_session_uint32_t::update(Session *session, set_var *var)
{
  uint64_t tmp= var->getInteger();

  /* Don't use bigger value than given with --maximum-variable-name=.. */
  if ((uint32_t) tmp > max_system_variables.*offset)
  {
    throw_bounds_warning(session, true, true, getName(), (int64_t) tmp);
    tmp= max_system_variables.*offset;
  }

  if (option_limits)
    tmp= (uint32_t) fix_unsigned(session, tmp, *option_limits);
  else if (tmp > UINT32_MAX)
  {
    tmp= UINT32_MAX;
    throw_bounds_warning(session, true, true, getName(), int64_t(var->getInteger()));
  }

  if (var->type == OPT_GLOBAL)
     global_system_variables.*offset= (uint32_t) tmp;
   else
     session->variables.*offset= (uint32_t) tmp;

   return 0;
 }


 void sys_var_session_uint32_t::set_default(Session *session, sql_var_t type)
 {
   if (type == OPT_GLOBAL)
   {
     bool not_used;
     /* We will not come here if option_limits is not set */
     global_system_variables.*offset=
       (uint32_t) getopt_ull_limit_value((uint32_t) option_limits->def_value, *option_limits, &not_used);
   }
   else
     session->variables.*offset= global_system_variables.*offset;
 }


unsigned char *sys_var_session_uint32_t::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL
    ? (unsigned char*) &(global_system_variables.*offset)
    : (unsigned char*) &(session->variables.*offset);
}


bool sys_var_session_ha_rows::update(Session *session, set_var *var)
{
  uint64_t tmp= var->getInteger();

  /* Don't use bigger value than given with --maximum-variable-name=.. */
  if ((ha_rows) tmp > max_system_variables.*offset)
    tmp= max_system_variables.*offset;

  if (option_limits)
    tmp= (ha_rows) fix_unsigned(session, tmp, *option_limits);
  if (var->type == OPT_GLOBAL)
  {
    /* Lock is needed to make things safe on 32 bit systems */
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset= (ha_rows) tmp;
  }
  else
  {
    session->variables.*offset= (ha_rows) tmp;
  }

  return 0;
}


void sys_var_session_ha_rows::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
  {
    bool not_used;
    /* We will not come here if option_limits is not set */
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset=
      (ha_rows) getopt_ull_limit_value((ha_rows) option_limits->def_value, *option_limits, &not_used);
  }
  else
  {
    session->variables.*offset= global_system_variables.*offset;
  }
}


unsigned char *sys_var_session_ha_rows::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL
    ? (unsigned char*) &(global_system_variables.*offset)
    : (unsigned char*) &(session->variables.*offset);
}

bool sys_var_session_uint64_t::check(Session *session, set_var *var)
{
  var->updateValue();
  return (check_func && (*check_func)(session, var));
}

bool sys_var_session_uint64_t::update(Session *session,  set_var *var)
{
  uint64_t tmp= var->getInteger();

  if (tmp > max_system_variables.*offset)
  {
    throw_bounds_warning(session, true, true, getName(), (int64_t) tmp);
    tmp= max_system_variables.*offset;
  }

  if (option_limits)
    tmp= fix_unsigned(session, tmp, *option_limits);
  if (var->type == OPT_GLOBAL)
  {
    /* Lock is needed to make things safe on 32 bit systems */
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset= (uint64_t) tmp;
  }
  else
  {
    session->variables.*offset= (uint64_t) tmp;
  }

  return 0;
}


void sys_var_session_uint64_t::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
  {
    bool not_used;
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset=
      getopt_ull_limit_value((uint64_t) option_limits->def_value, *option_limits, &not_used);
  }
  else
  {
    session->variables.*offset= global_system_variables.*offset;
  }
}


unsigned char *sys_var_session_uint64_t::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL
    ? (unsigned char*) &(global_system_variables.*offset)
    : (unsigned char*) &(session->variables.*offset);
}

bool sys_var_session_size_t::check(Session *session, set_var *var)
{
  var->updateValue();
  return (check_func && (*check_func)(session, var));
}

bool sys_var_session_size_t::update(Session *session,  set_var *var)
{
  size_t tmp= size_t(var->getInteger());

  if (tmp > max_system_variables.*offset)
    tmp= max_system_variables.*offset;

  if (option_limits)
    tmp= fix_size_t(session, tmp, *option_limits);
  if (var->type == OPT_GLOBAL)
  {
    /* Lock is needed to make things safe on 32 bit systems */
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset= tmp;
  }
  else
  {
    session->variables.*offset= tmp;
  }

  return 0;
}


void sys_var_session_size_t::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
  {
    bool not_used;
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset=
      (size_t)getopt_ull_limit_value((size_t) option_limits->def_value, *option_limits, &not_used);
  }
  else
  {
    session->variables.*offset= global_system_variables.*offset;
  }
}


unsigned char *sys_var_session_size_t::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL
    ? (unsigned char*) &(global_system_variables.*offset) 
    : (unsigned char*) &(session->variables.*offset);
}

bool sys_var_session_bool::check(Session *session, set_var *var)
{
  return check_enum(session, var, &bool_typelib);
}

bool sys_var_session_bool::update(Session *session,  set_var *var)
{
  if (var->type == OPT_GLOBAL)
    global_system_variables.*offset= bool(var->getInteger());
  else
    session->variables.*offset= bool(var->getInteger());

  return 0;
}


void sys_var_session_bool::set_default(Session *session,  sql_var_t type)
{
  if (type == OPT_GLOBAL)
    global_system_variables.*offset= (bool) option_limits->def_value;
  else
    session->variables.*offset= global_system_variables.*offset;
}


unsigned char *sys_var_session_bool::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL
    ? (unsigned char*) &(global_system_variables.*offset)
    : (unsigned char*) &(session->variables.*offset);
}


bool sys_var::check_enum(Session *, set_var *var, const TYPELIB *enum_names)
{
  char buff[STRING_BUFFER_USUAL_SIZE];
  const char *value;
  String str(buff, sizeof(buff), system_charset_info), *res;

  if (var->value->result_type() == STRING_RESULT)
  {
    res= var->value->val_str(&str);
    if (res == NULL)
    {
      value= "NULL";
      goto err;
    }

    uint64_t tmp_val= enum_names->find_type(res->ptr(), res->length(), true);
    if (tmp_val == 0)
    {
      value= res->c_ptr();
      goto err;
    }
    var->setValue(tmp_val-1);
  }
  else
  {
    uint64_t tmp= var->value->val_int();
    if (tmp >= enum_names->count)
    {
      internal::llstr(tmp,buff);
      value=buff;				// Wrong value is here
      goto err;
    }
    var->setValue(tmp);	// Save for update
  }
  return 0;

err:
  my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name.c_str(), value);
  return 1;
}


/**
  Return an Item for a variable.

  Used with @@[global.]variable_name.

  If type is not given, return local value if exists, else global.
*/

Item *sys_var::item(Session *session, sql_var_t var_type)
{
  if (check_type(var_type))
  {
    if (var_type != OPT_DEFAULT)
    {
      my_error(ER_INCORRECT_GLOBAL_LOCAL_VAR, MYF(0), name.c_str(), var_type == OPT_GLOBAL ? "SESSION" : "GLOBAL");
      return 0;
    }
    /* As there was no local variable, return the global value */
    var_type= OPT_GLOBAL;
  }
  boost::mutex::scoped_lock lock(session->catalog().systemVariableLock());
  switch (show_type()) 
  {
  case SHOW_LONG:
  case SHOW_INT:
  {
    uint32_t value= *(uint*) value_ptr(session, var_type);
    return new Item_uint((uint64_t) value);
  }
  case SHOW_LONGLONG:
  {
    int64_t value= *(int64_t*) value_ptr(session, var_type);
    return new Item_int(value);
  }
  case SHOW_DOUBLE:
  {
    double value= *(double*) value_ptr(session, var_type);
    /* 6, as this is for now only used with microseconds */
    return new Item_float(value, 6);
  }
  case SHOW_HA_ROWS:
  {
    ha_rows value= *(ha_rows*) value_ptr(session, var_type);
    return new Item_int((uint64_t) value);
  }
  case SHOW_SIZE:
  {
    size_t value= *(size_t*) value_ptr(session, var_type);
    return new Item_int((uint64_t) value);
  }
  case SHOW_MY_BOOL:
  {
    int32_t value= *(bool*) value_ptr(session, var_type);
    return new Item_int(value, 1);
  }
  case SHOW_CHAR_PTR:
  {
    if (const char *str= *(char**) value_ptr(session, var_type))
    {
      uint32_t length= strlen(str);
      return new Item_string(session->mem.strdup(str, length), length, system_charset_info, DERIVATION_SYSCONST);
    }
    Item* tmp= new Item_null();
    tmp->collation.set(system_charset_info, DERIVATION_SYSCONST);
    return tmp;
  }
  case SHOW_CHAR:
  {
    if (const char* str= (char*) value_ptr(session, var_type))
      return new Item_string(str_ref(str), system_charset_info, DERIVATION_SYSCONST);
    Item* tmp= new Item_null();
    tmp->collation.set(system_charset_info, DERIVATION_SYSCONST);
    return tmp;
  }
  default:
    my_error(ER_VAR_CANT_BE_READ, MYF(0), name.c_str());
  }
  return NULL;
}


bool sys_var_session_enum::update(Session *session, set_var *var)
{
  if (var->type == OPT_GLOBAL)
    global_system_variables.*offset= var->getInteger();
  else
    session->variables.*offset= var->getInteger();
  return 0;
}


void sys_var_session_enum::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
    global_system_variables.*offset= (uint32_t) option_limits->def_value;
  else
    session->variables.*offset= global_system_variables.*offset;
}


unsigned char *sys_var_session_enum::value_ptr(Session *session, sql_var_t type)
{
  uint32_t tmp= type == OPT_GLOBAL ? global_system_variables.*offset : session->variables.*offset;
  return (unsigned char*) enum_names->type_names[tmp];
}

bool sys_var_session_bit::check(Session *session, set_var *var)
{
  return check_enum(session, var, &bool_typelib) || (check_func && (*check_func)(session, var));
}

bool sys_var_session_bit::update(Session *session, set_var *var)
{
  return (*update_func)(session, var);
}


unsigned char *sys_var_session_bit::value_ptr(Session *session, sql_var_t)
{
  /*
    If reverse is 0 (default) return 1 if bit is set.
    If reverse is 1, return 0 if bit is set
  */
  session->sys_var_tmp.bool_value= (session->options & bit_flag) ? !reverse : reverse;
  return (unsigned char*) &session->sys_var_tmp.bool_value;
}


bool sys_var_collation_sv::update(Session *session, set_var *var)
{
  const charset_info_st *tmp;

  if (var->value->result_type() == STRING_RESULT)
  {
    char buff[STRING_BUFFER_USUAL_SIZE];
    String str(buff,sizeof(buff), system_charset_info), *res;
    if (!(res=var->value->val_str(&str)))
    {
      boost::throw_exception(invalid_option_value(var->var->getName()) << invalid_value(std::string("NULL")));
      return 1;
    }
    if (!(tmp=get_charset_by_name(res->c_ptr())))
    {
      my_error(ER_UNKNOWN_COLLATION, MYF(0), res->c_ptr());
      boost::throw_exception(invalid_option_value(var->var->getName()) << invalid_value(std::string(res->c_ptr())));
      return 1;
    }
  }
  else // INT_RESULT
  {
    if (!(tmp=get_charset((int) var->value->val_int())))
    {
      char buf[20];
      internal::int10_to_str((int) var->value->val_int(), buf, -10);
      my_error(ER_UNKNOWN_COLLATION, MYF(0), buf);
      boost::throw_exception(invalid_option_value(var->var->getName()) << invalid_value(boost::lexical_cast<std::string>(var->value->val_int())));
      return 1;
    }
  }
  if (var->type == OPT_GLOBAL)
    global_system_variables.*offset= tmp;
  else
  {
    session->variables.*offset= tmp;
  }
  return 0;
}


void sys_var_collation_sv::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
    global_system_variables.*offset= *global_default;
  else
  {
    session->variables.*offset= global_system_variables.*offset;
  }
}


unsigned char *sys_var_collation_sv::value_ptr(Session *session, sql_var_t type)
{
  const charset_info_st *cs= type == OPT_GLOBAL ? global_system_variables.*offset : session->variables.*offset;
  return cs ? (unsigned char*) cs->name : (unsigned char*) "NULL";
}

/****************************************************************************/

bool sys_var_timestamp::update(Session *session,  set_var *var)
{
  session->times.set_time(time_t(var->getInteger()));
  return 0;
}


void sys_var_timestamp::set_default(Session *session, sql_var_t)
{
  session->times.resetUserTime();
}


unsigned char *sys_var_timestamp::value_ptr(Session *session, sql_var_t)
{
  session->sys_var_tmp.int32_t_value= (int32_t) session->times.getCurrentTimestampEpoch();
  return (unsigned char*) &session->sys_var_tmp.int32_t_value;
}


bool sys_var_last_insert_id::update(Session *session, set_var *var)
{
  session->first_successful_insert_id_in_prev_stmt= var->getInteger();
  return 0;
}


unsigned char *sys_var_last_insert_id::value_ptr(Session *session, sql_var_t)
{
  /*
    this tmp var makes it robust againt change of type of
    read_first_successful_insert_id_in_prev_stmt().
  */
  session->sys_var_tmp.uint64_t_value=
    session->read_first_successful_insert_id_in_prev_stmt();
  return (unsigned char*) &session->sys_var_tmp.uint64_t_value;
}

bool sys_var_session_lc_time_names::update(Session *session, set_var *var)
{
  MY_LOCALE *locale_match;

  if (var->value->result_type() == INT_RESULT)
  {
    if (!(locale_match= my_locale_by_number((uint32_t) var->value->val_int())))
    {
      char buf[DECIMAL_LONGLONG_DIGITS];
      internal::int10_to_str((int) var->value->val_int(), buf, -10);
      my_printf_error(ER_UNKNOWN_ERROR, "Unknown locale: '%s'", MYF(0), buf);
      return 1;
    }
  }
  else // STRING_RESULT
  {
    char buff[6];
    String str(buff, sizeof(buff), &my_charset_utf8_general_ci), *res;
    if (!(res=var->value->val_str(&str)))
    {
      my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name.c_str(), "NULL");
      return 1;
    }
    const char *locale_str= res->c_ptr();
    if (!(locale_match= my_locale_by_name(locale_str)))
    {
      my_printf_error(ER_UNKNOWN_ERROR,
                      "Unknown locale: '%s'", MYF(0), locale_str);
      return 1;
    }
  }

  if (var->type == OPT_GLOBAL)
    global_system_variables.lc_time_names= locale_match;
  else
    session->variables.lc_time_names= locale_match;
  return 0;
}


unsigned char *sys_var_session_lc_time_names::value_ptr(Session *session, sql_var_t type)
{
  return type == OPT_GLOBAL 
    ? (unsigned char *) global_system_variables.lc_time_names->name 
    : (unsigned char *) session->variables.lc_time_names->name;
}


void sys_var_session_lc_time_names::set_default(Session *session, sql_var_t type)
{
  if (type == OPT_GLOBAL)
    global_system_variables.lc_time_names= my_default_lc_time_names;
  else
    session->variables.lc_time_names= global_system_variables.lc_time_names;
}

/*
  Handling of microseoncds given as seconds.part_seconds

  NOTES
    The argument to long query time is in seconds in decimal
    which is converted to uint64_t integer holding microseconds for storage.
    This is used for handling long_query_time
*/

bool sys_var_microseconds::update(Session *session, set_var *var)
{
  double num= var->value->val_real();
  int64_t microseconds;
  if (num > (double) option_limits->max_value)
    num= (double) option_limits->max_value;
  if (num < (double) option_limits->min_value)
    num= (double) option_limits->min_value;
  microseconds= (int64_t) (num * 1000000.0 + 0.5);
  if (var->type == OPT_GLOBAL)
  {
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    (global_system_variables.*offset)= microseconds;
  }
  else
    session->variables.*offset= microseconds;
  return 0;
}


void sys_var_microseconds::set_default(Session *session, sql_var_t type)
{
  int64_t microseconds= (int64_t) (option_limits->def_value * 1000000.0);
  if (type == OPT_GLOBAL)
  {
    boost::mutex::scoped_lock scopedLock(session->catalog().systemVariableLock());
    global_system_variables.*offset= microseconds;
  }
  else
    session->variables.*offset= microseconds;
}

/*
  Functions to update session->options bits
*/

static bool set_option_bit(Session *session, set_var *var)
{
  sys_var_session_bit *sys_var= ((sys_var_session_bit*) var->var);
  if ((var->getInteger() != 0) == sys_var->reverse)
    session->options&= ~sys_var->bit_flag;
  else
    session->options|= sys_var->bit_flag;
  return 0;
}


static bool set_option_autocommit(Session *session, set_var *var)
{
  bool success= true;
  /* The test is negative as the flag we use is NOT autocommit */

  uint64_t org_options= session->options;
  uint64_t new_options= session->options;

  if (var->getInteger() != 0)
    new_options&= ~((sys_var_session_bit*) var->var)->bit_flag;
  else
    new_options|= ((sys_var_session_bit*) var->var)->bit_flag;

  if ((org_options ^ new_options) & OPTION_NOT_AUTOCOMMIT)
  {
    if ((org_options & OPTION_NOT_AUTOCOMMIT))
    {
      success= session->endActiveTransaction();
      /* We changed to auto_commit mode */
      session->options&= ~(uint64_t) (OPTION_BEGIN);
      session->server_status|= SERVER_STATUS_AUTOCOMMIT;
    }
    else
    {
      session->server_status&= ~SERVER_STATUS_AUTOCOMMIT;
    }
  }

  if (var->getInteger() != 0)
    session->options&= ~((sys_var_session_bit*) var->var)->bit_flag;
  else
    session->options|= ((sys_var_session_bit*) var->var)->bit_flag;

  return not success;
}

static int check_pseudo_thread_id(Session *, set_var *var)
{
  var->updateValue();
  return 0;
}

static unsigned char *get_warning_count(Session *session)
{
  session->sys_var_tmp.uint32_t_value=
    (session->warn_count[(uint32_t) DRIZZLE_ERROR::WARN_LEVEL_NOTE] +
     session->warn_count[(uint32_t) DRIZZLE_ERROR::WARN_LEVEL_ERROR] +
     session->warn_count[(uint32_t) DRIZZLE_ERROR::WARN_LEVEL_WARN]);
  return (unsigned char*) &session->sys_var_tmp.uint32_t_value;
}

static unsigned char *get_error_count(Session *session)
{
  session->sys_var_tmp.uint32_t_value=
    session->warn_count[(uint32_t) DRIZZLE_ERROR::WARN_LEVEL_ERROR];
  return (unsigned char*) &session->sys_var_tmp.uint32_t_value;
}


/**
  Get the tmpdir that was specified or chosen by default.

  This is necessary because if the user does not specify a temporary
  directory via the command line, one is chosen based on the environment
  or system defaults.  But we can't just always use drizzle_tmpdir, because
  that is actually a call to my_tmpdir() which cycles among possible
  temporary directories.

  @param session		thread handle

  @retval
    ptr		pointer to NUL-terminated string
*/
static unsigned char *get_tmpdir(Session *)
{
  assert(drizzle_tmpdir.size());
  return (unsigned char*)drizzle_tmpdir.c_str();
}

/****************************************************************************
  Main handling of variables:
  - Initialisation
  - Searching during parsing
  - Update loop
****************************************************************************/

/**
  Find variable name in option my_getopt structure used for
  command line args.

  @param opt	option structure array to search in
  @param name	variable name

  @retval
    0		Error
  @retval
    ptr		pointer to option structure
*/

static option* find_option(struct option *opt, const char *name)
{
  uint32_t length= strlen(name);
  for (; opt->name; opt++)
  {
    if (not getopt_compare_strings(opt->name, name, length) and not opt->name[length])
    {
      /*
      Only accept the option if one can set values through it.
      If not, there is no default value or limits in the option.
      */
      return opt->value ? opt : NULL;
    }
  }
  return NULL;
}





/*
  Constructs an array of system variables for display to the user.

  SYNOPSIS
    enumerate_sys_vars()
    session         current thread

  RETURN VALUES
    pointer     Array of drizzle_show_var elements for display
    NULL        FAILURE
*/

drizzle_show_var* enumerate_sys_vars(Session *session)
{
  drizzle_show_var *result= new (session->mem) drizzle_show_var[system_variable_map.size() + 1];
  drizzle_show_var *show= result;
  BOOST_FOREACH(SystemVariableMap::const_reference iter, system_variable_map)
  {
    sys_var *var= iter.second;
    show->name= var->getName().c_str();
    show->value= (char*) var;
    show->type= SHOW_SYS;
    ++show;
  }

  /* make last element empty */
  memset(show, 0, sizeof(drizzle_show_var));
  return result;
}

void add_sys_var_to_list(sys_var *var)
{
  string lower_name(var->getName());
  boost::to_lower(lower_name);

  /* this fails if there is a conflicting variable name. */
  if (system_variable_map.count(lower_name))
  {
    errmsg_printf(error::ERROR, _("Variable named %s already exists!\n"), var->getName().c_str());
    throw exception();
  } 

  pair<SystemVariableMap::iterator, bool> ret= system_variable_map.insert(make_pair(lower_name, var));
  if (ret.second == false)
  {
    errmsg_printf(error::ERROR, _("Could not add Variable: %s\n"), var->getName().c_str());
    throw exception();
  }
}

void add_sys_var_to_list(sys_var *var, struct option *long_options)
{
  add_sys_var_to_list(var);
  var->setOptionLimits(find_option(long_options, var->getName().c_str()));
}

/*
  Initialize the system variables

  SYNOPSIS
    sys_var_init()

  RETURN VALUES
    0           SUCCESS
    otherwise   FAILURE
*/

int sys_var_init()
{
  try
  {
    add_sys_var_to_list(&sys_auto_increment_increment, my_long_options);
    add_sys_var_to_list(&sys_auto_increment_offset, my_long_options);
    add_sys_var_to_list(&sys_autocommit, my_long_options);
    add_sys_var_to_list(&sys_back_log, my_long_options);
    add_sys_var_to_list(&sys_basedir, my_long_options);
    add_sys_var_to_list(&sys_big_selects, my_long_options);
    add_sys_var_to_list(&sys_branch, my_long_options);
    add_sys_var_to_list(&sys_buffer_results, my_long_options);
    add_sys_var_to_list(&sys_bulk_insert_buff_size, my_long_options);
    add_sys_var_to_list(&sys_collation_server, my_long_options);
    add_sys_var_to_list(&sys_completion_type, my_long_options);
    add_sys_var_to_list(&sys_datadir, my_long_options);
    add_sys_var_to_list(&sys_div_precincrement, my_long_options);
    add_sys_var_to_list(&sys_error_count, my_long_options);
    add_sys_var_to_list(&sys_foreign_key_checks, my_long_options);
    add_sys_var_to_list(&sys_group_concat_max_len, my_long_options);
    add_sys_var_to_list(&sys_hostname, my_long_options);
    add_sys_var_to_list(&sys_identity, my_long_options);
    add_sys_var_to_list(&sys_join_buffer_size, my_long_options);
    add_sys_var_to_list(&sys_last_insert_id, my_long_options);
    add_sys_var_to_list(&sys_lc_time_names, my_long_options);
    add_sys_var_to_list(&sys_max_allowed_packet, my_long_options);
    add_sys_var_to_list(&sys_max_error_count, my_long_options);
    add_sys_var_to_list(&sys_max_heap_table_size, my_long_options);
    add_sys_var_to_list(&sys_max_join_size, my_long_options);
    add_sys_var_to_list(&sys_max_length_for_sort_data, my_long_options);
    add_sys_var_to_list(&sys_max_seeks_for_key, my_long_options);
    add_sys_var_to_list(&sys_max_sort_length, my_long_options);
    add_sys_var_to_list(&sys_max_write_lock_count, my_long_options);
    add_sys_var_to_list(&sys_min_examined_row_limit, my_long_options);
    add_sys_var_to_list(&sys_optimizer_prune_level, my_long_options);
    add_sys_var_to_list(&sys_optimizer_search_depth, my_long_options);
    add_sys_var_to_list(&sys_pid_file, my_long_options);
    add_sys_var_to_list(&sys_plugin_dir, my_long_options);
    add_sys_var_to_list(&sys_preload_buff_size, my_long_options);
    add_sys_var_to_list(&sys_pseudo_thread_id, my_long_options);
    add_sys_var_to_list(&sys_query_alloc_block_size, my_long_options);
    add_sys_var_to_list(&sys_query_prealloc_size, my_long_options);
    add_sys_var_to_list(&sys_range_alloc_block_size, my_long_options);
    add_sys_var_to_list(&sys_read_buff_size, my_long_options);
    add_sys_var_to_list(&sys_read_rnd_buff_size, my_long_options);
    add_sys_var_to_list(&sys_release_id, my_long_options);
    add_sys_var_to_list(&sys_replicate_query, my_long_options);
    add_sys_var_to_list(&sys_revid, my_long_options);
    add_sys_var_to_list(&sys_revno, my_long_options);
    add_sys_var_to_list(&sys_scheduler, my_long_options);
    add_sys_var_to_list(&sys_secure_file_priv, my_long_options);
    add_sys_var_to_list(&sys_select_limit, my_long_options);
    add_sys_var_to_list(&sys_server_id, my_long_options);
    add_sys_var_to_list(&sys_server_uuid, my_long_options);
    add_sys_var_to_list(&sys_sort_buffer, my_long_options);
    add_sys_var_to_list(&sys_sql_notes, my_long_options);
    add_sys_var_to_list(&sys_sql_warnings, my_long_options);
    add_sys_var_to_list(&sys_storage_engine, my_long_options);
    add_sys_var_to_list(&sys_table_cache_size, my_long_options);
    add_sys_var_to_list(&sys_table_def_size, my_long_options);
    add_sys_var_to_list(&sys_table_lock_wait_timeout, my_long_options);
    add_sys_var_to_list(&sys_thread_stack_size, my_long_options);
    add_sys_var_to_list(&sys_timed_mutexes, my_long_options);
    add_sys_var_to_list(&sys_timestamp, my_long_options);
    add_sys_var_to_list(&sys_tmp_table_size, my_long_options);
    add_sys_var_to_list(&sys_tmpdir, my_long_options);
    add_sys_var_to_list(&sys_transaction_message_threshold, my_long_options);
    add_sys_var_to_list(&sys_tx_isolation, my_long_options);
    add_sys_var_to_list(&sys_unique_checks, my_long_options);
    add_sys_var_to_list(&sys_version, my_long_options);
    add_sys_var_to_list(&sys_version_comment, my_long_options);
    add_sys_var_to_list(&sys_version_compile_machine, my_long_options);
    add_sys_var_to_list(&sys_version_compile_os, my_long_options);
    add_sys_var_to_list(&sys_version_compile_vendor, my_long_options);
    add_sys_var_to_list(&sys_warning_count, my_long_options);
  }
  catch (std::exception&)
  {
    errmsg_printf(error::ERROR, _("Failed to initialize system variables"));
    return 1;
  }
  return 0;
}


/**
  Find a user set-table variable.

  @param name	   Name of system variable to find

  @retval
    pointer	pointer to variable definitions
  @retval
    0		Unknown variable (error message is given)
*/

sys_var *find_sys_var(const std::string &name)
{
  if (sys_var* ptr= find_ptr2(system_variable_map, boost::to_lower_copy(name)))
    return ptr;
  my_error(ER_UNKNOWN_SYSTEM_VARIABLE, MYF(0), name.c_str());
  return NULL;
}


/****************************************************************************
 Functions to handle table_type
****************************************************************************/

unsigned char *sys_var_session_storage_engine::value_ptr(Session *session, sql_var_t type)
{
  plugin::StorageEngine *engine= type == OPT_GLOBAL
    ? global_system_variables.*offset
    : session->variables.*offset;
  return (unsigned char *) session->mem.strdup(engine->getName());
}


void sys_var_session_storage_engine::set_default(Session *session, sql_var_t type)
{
  plugin::StorageEngine *new_value, **value;
  if (type == OPT_GLOBAL)
  {
    value= &(global_system_variables.*offset);
    new_value= myisam_engine;
  }
  else
  {
    value= &(session->variables.*offset);
    new_value= global_system_variables.*offset;
  }
  assert(new_value);
  *value= new_value;
}


bool sys_var_session_storage_engine::update(Session *session, set_var *var)
{
  char buff[STRING_BUFFER_USUAL_SIZE];
  const char *name_value;
  String str(buff, sizeof(buff), &my_charset_utf8_general_ci), *res;

  plugin::StorageEngine *tmp= NULL;
  plugin::StorageEngine **value= NULL;
    
  if (var->value->result_type() == STRING_RESULT)
  {
    res= var->value->val_str(&str);
    if (res == NULL || res->ptr() == NULL)
    {
      name_value= "NULL";
      goto err;
    }
    else
    {
      const std::string engine_name(res->ptr());
      tmp= plugin::StorageEngine::findByName(*session, engine_name);
      if (tmp == NULL)
      {
        name_value= res->c_ptr();
        goto err;
      }
    }
  }
  else
  {
    name_value= "unknown";
  }

  value= &(global_system_variables.*offset);
   if (var->type != OPT_GLOBAL)
     value= &(session->variables.*offset);
  if (*value != tmp)
  {
    *value= tmp;
  }
  return 0;
err:
  my_error(ER_UNKNOWN_STORAGE_ENGINE, MYF(0), name_value);
  return 1;
}

} /* namespace drizzled */