mariadb/sql/temporary_tables.cc

/*
  Copyright (c) 2016, 2021, MariaDB Corporation.

  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
*/

/**
  All methods pertaining to temporary tables.
*/

#include "mariadb.h"
#include "sql_acl.h"                            /* TMP_TABLE_ACLS */
#include "sql_base.h"                           /* tdc_create_key */
#include "lock.h"                               /* mysql_lock_remove */
#include "log_event.h"                          /* Query_log_event */
#include "sql_show.h"                           /* append_identifier */
#include "sql_handler.h"                        /* mysql_ha_rm_temporary_tables */
#include "rpl_rli.h"                            /* rpl_group_info */

#define IS_USER_TABLE(A) ((A->tmp_table == TRANSACTIONAL_TMP_TABLE) || \
                          (A->tmp_table == NON_TRANSACTIONAL_TMP_TABLE))

/**
  Check whether temporary tables exist. The decision is made based on the
  existence of TMP_TABLE_SHAREs in Open_tables_state::temporary_tables list.

  @return false                       Temporary tables exist
          true                        No temporary table exist
*/
bool THD::has_thd_temporary_tables()
{
  DBUG_ENTER("THD::has_thd_temporary_tables");
  bool result= (temporary_tables && !temporary_tables->is_empty());
  DBUG_RETURN(result);
}


/**
  Create a temporary table, open it and return the TABLE handle.

  @param frm  [IN]                    Binary frm image
  @param path [IN]                    File path (without extension)
  @param db   [IN]                    Schema name
  @param table_name [IN]              Table name

  @return Success                     A pointer to table object
          Failure                     NULL
*/
TABLE *THD::create_and_open_tmp_table(LEX_CUSTRING *frm,
                                      const char *path,
                                      const char *db,
                                      const char *table_name,
                                      bool open_internal_tables)
{
  DBUG_ENTER("THD::create_and_open_tmp_table");

  TMP_TABLE_SHARE *share;
  TABLE *table= NULL;

  if ((share= create_temporary_table(frm, path, db, table_name)))
  {
    open_options|= HA_OPEN_FOR_CREATE;
    table= open_temporary_table(share, table_name);
    open_options&= ~HA_OPEN_FOR_CREATE;

    /*
      Failed to open a temporary table instance. As we are not passing
      the created TMP_TABLE_SHARE to the caller, we must remove it from
      the list and free it here.
    */
    if (!table)
    {
      /* Remove the TABLE_SHARE from the list of temporary tables. */
      temporary_tables->remove(share);

      /* Free the TMP_TABLE_SHARE. */
      free_tmp_table_share(share, false);
      DBUG_RETURN(0);
    }

    /* Open any related tables */
    if (open_internal_tables && table->internal_tables &&
        open_and_lock_internal_tables(table, true))
    {
      drop_temporary_table(table, NULL, false);
      DBUG_RETURN(0);
    }
  }

  DBUG_RETURN(table);
}


/**
  Check whether an open table with db/table name is in use.

  @param db [IN]                      Database name
  @param table_name [IN]              Table name
  @param state [IN]                   State of temp table to open

  @return Success                     Pointer to first used table instance.
          Failure                     NULL
*/
TABLE *THD::find_temporary_table(const char *db,
                                 const char *table_name,
                                 Temporary_table_state state)
{
  DBUG_ENTER("THD::find_temporary_table");

  TABLE *table;
  char key[MAX_DBKEY_LENGTH];
  uint key_length;
  bool locked;

  if (!has_temporary_tables())
  {
    DBUG_RETURN(NULL);
  }

  key_length= create_tmp_table_def_key(key, db, table_name);

  locked= lock_temporary_tables();
  table=  find_temporary_table(key, key_length, state);
  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(table);
}


/**
  Check whether an open table specified in TABLE_LIST is in use.

  @return tl [IN]                     TABLE_LIST

  @return Success                     Pointer to first used table instance.
          Failure                     NULL
*/
TABLE *THD::find_temporary_table(const TABLE_LIST *tl,
                                 Temporary_table_state state)
{
  DBUG_ENTER("THD::find_temporary_table");
  TABLE *table= find_temporary_table(tl->get_db_name().str,
                                     tl->get_table_name().str,
                                     state);
  DBUG_RETURN(table);
}


/**
  Check whether a temporary table exists with the specified key.
  The key, in this case, is not the usual key used for temporary tables.
  It does not contain server_id & pseudo_thread_id. This function is
  essentially used use to check whether there is any temporary table
  which _shadows_ a base table.
  (see: Query_cache::send_result_to_client())

  @return Success                     A pointer to table share object
          Failure                     NULL
*/
TMP_TABLE_SHARE *THD::find_tmp_table_share_w_base_key(const char *key,
                                                      uint key_length)
{
  DBUG_ENTER("THD::find_tmp_table_share_w_base_key");

  TMP_TABLE_SHARE *share;
  TMP_TABLE_SHARE *result= NULL;
  bool locked;

  if (!has_temporary_tables())
  {
    DBUG_RETURN(NULL);
  }

  locked= lock_temporary_tables();

  All_tmp_tables_list::Iterator it(*temporary_tables);
  while ((share= it++))
  {
    if ((share->table_cache_key.length - TMP_TABLE_KEY_EXTRA) == key_length
        && !memcmp(share->table_cache_key.str, key, key_length))
    {
      result= share;
    }
  }

  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(result);
}


/**
  Lookup the TMP_TABLE_SHARE using the given db/table_name.The server_id and
  pseudo_thread_id used to generate table definition key is taken from THD
  (see create_tmp_table_def_key()). Return NULL is none found.

  @return Success                     A pointer to table share object
          Failure                     NULL
*/
TMP_TABLE_SHARE *THD::find_tmp_table_share(const char *db,
                                           const char *table_name)
{
  DBUG_ENTER("THD::find_tmp_table_share");

  TMP_TABLE_SHARE *share;
  char key[MAX_DBKEY_LENGTH];
  uint key_length;

  key_length= create_tmp_table_def_key(key, db, table_name);
  share= find_tmp_table_share(key, key_length);

  DBUG_RETURN(share);
}


/**
  Lookup TMP_TABLE_SHARE using the specified TABLE_LIST element.
  Return NULL is none found.

  @param tl [IN]                      Table

  @return Success                     A pointer to table share object
          Failure                     NULL
*/
TMP_TABLE_SHARE *THD::find_tmp_table_share(const TABLE_LIST *tl)
{
  DBUG_ENTER("THD::find_tmp_table_share");
  TMP_TABLE_SHARE *share= find_tmp_table_share(tl->get_db_name().str,
                                               tl->get_table_name().str);
  DBUG_RETURN(share);
}


/**
  Lookup TMP_TABLE_SHARE using the specified table definition key.
  Return NULL is none found.

  @return Success                     A pointer to table share object
          Failure                     NULL
*/
TMP_TABLE_SHARE *THD::find_tmp_table_share(const char *key, size_t key_length)
{
  DBUG_ENTER("THD::find_tmp_table_share");

  TMP_TABLE_SHARE *share;
  TMP_TABLE_SHARE *result= NULL;
  bool locked;

  if (!has_temporary_tables())
  {
    DBUG_RETURN(NULL);
  }

  locked= lock_temporary_tables();

  All_tmp_tables_list::Iterator it(*temporary_tables);
  while ((share= it++))
  {
    if (share->table_cache_key.length == key_length &&
        !(memcmp(share->table_cache_key.str, key, key_length)))
    {
      result= share;
      break;
    }
  }

  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(result);
}


/**
  Find a temporary table specified by TABLE_LIST instance in the open table
  list and prepare its TABLE instance for use. If

  This function tries to resolve this table in the list of temporary tables
  of this thread. Temporary tables are thread-local and "shadow" base
  tables with the same name.

  @note In most cases one should use THD::open_tables() instead
        of this call.

  @note One should finalize process of opening temporary table for table
        list element by calling open_and_process_table(). This function
        is responsible for table version checking and handling of merge
        tables.

  @note We used to check global_read_lock before opening temporary tables.
        However, that limitation was artificial and is removed now.

  @param tl [IN]                      TABLE_LIST

  @return Error status.
    @retval false                     On success. If a temporary table exists
                                      for the given key, tl->table is set.
    @retval true                      On error. my_error() has been called.
*/
bool THD::open_temporary_table(TABLE_LIST *tl)
{
  DBUG_ENTER("THD::open_temporary_table");
  DBUG_PRINT("enter", ("table: '%s'.'%s'", tl->db.str, tl->table_name.str));

  TMP_TABLE_SHARE *share;
  TABLE *table= NULL;

  /*
    Code in open_table() assumes that TABLE_LIST::table can be non-zero only
    for pre-opened temporary tables.
  */
  DBUG_ASSERT(tl->table == NULL);

  /*
    This function should not be called for cases when derived or I_S
    tables can be met since table list elements for such tables can
    have invalid db or table name.
    Instead THD::open_tables() should be used.
  */
  DBUG_ASSERT(!tl->derived);
  DBUG_ASSERT(!tl->schema_table);
  DBUG_ASSERT(has_temporary_tables() ||
              (rgi_slave && rgi_slave->is_parallel_exec));

  if (tl->open_type == OT_BASE_ONLY)
  {
    DBUG_PRINT("info", ("skip_temporary is set or no temporary tables"));
    DBUG_RETURN(false);
  }

  if (!tl->db.str)
  {
    DBUG_PRINT("info",
               ("Table reference to a temporary table must have database set"));
    DBUG_RETURN(false);
  }

  /*
    Temporary tables are not safe for parallel replication. They were
    designed to be visible to one thread only, so have no table locking.
    Thus there is no protection against two conflicting transactions
    committing in parallel and things like that.

    So for now, anything that uses temporary tables will be serialised
    with anything before it, when using parallel replication.
  */

  if (rgi_slave &&
      rgi_slave->is_parallel_exec &&
      find_temporary_table(tl) &&
      wait_for_prior_commit())
    DBUG_RETURN(true);

  /*
    First check if there is a reusable open table available in the
    open table list.
  */
  if (find_and_use_tmp_table(tl, &table))
  {
    DBUG_RETURN(true);                          /* Error */
  }

  /*
    No reusable table was found. We will have to open a new instance.
  */
  if (!table && (share= find_tmp_table_share(tl)))
  {
    table= open_temporary_table(share, tl->get_table_name().str);
    /*
       Temporary tables are not safe for parallel replication. They were
       designed to be visible to one thread only, so have no table locking.
       Thus there is no protection against two conflicting transactions
       committing in parallel and things like that.

       So for now, anything that uses temporary tables will be serialised
       with anything before it, when using parallel replication.
    */
    if (table && rgi_slave &&
        rgi_slave->is_parallel_exec &&
        wait_for_prior_commit())
      DBUG_RETURN(true);

    if (!table && is_error())
      DBUG_RETURN(true);                        // Error when opening table
  }

  if (!table)
  {
    if (tl->open_type == OT_TEMPORARY_ONLY &&
        tl->open_strategy == TABLE_LIST::OPEN_NORMAL)
    {
      my_error(ER_NO_SUCH_TABLE, MYF(0), tl->db.str, tl->table_name.str);
      DBUG_RETURN(true);
    }
    DBUG_RETURN(false);
  }

#ifdef WITH_PARTITION_STORAGE_ENGINE
  if (tl->partition_names)
  {
    /* Partitioned temporary tables is not supported. */
    DBUG_ASSERT(!table->part_info);
    my_error(ER_PARTITION_CLAUSE_ON_NONPARTITIONED, MYF(0));
    DBUG_RETURN(true);
  }
#endif

  table->query_id= query_id;
  used|= THREAD_SPECIFIC_USED;

  /* It is neither a derived table nor non-updatable view. */
  tl->updatable= true;
  tl->table= table;

  table->init(this, tl);

  DBUG_PRINT("info", ("Using temporary table"));
  DBUG_RETURN(false);
}


/**
  Pre-open temporary tables corresponding to table list elements.

  @note One should finalize process of opening temporary tables
        by calling open_tables(). This function is responsible
        for table version checking and handling of merge tables.

  @param tl [IN]                      TABLE_LIST

  @return false                       On success. If a temporary table exists
                                      for the given element, tl->table is set.
          true                        On error. my_error() has been called.
*/
bool THD::open_temporary_tables(TABLE_LIST *tl)
{
  TABLE_LIST *first_not_own;
  DBUG_ENTER("THD::open_temporary_tables");

  if (!has_temporary_tables())
    DBUG_RETURN(0);

  first_not_own= lex->first_not_own_table();
  for (TABLE_LIST *table= tl; table && table != first_not_own;
       table= table->next_global)
  {
    if (table->derived || table->schema_table)
    {
      /*
        Derived and I_S tables will be handled by a later call to open_tables().
      */
      continue;
    }

    if (open_temporary_table(table))
    {
      DBUG_RETURN(true);
    }
  }

  DBUG_RETURN(false);
}


/**
  Close all temporary tables created by 'CREATE TEMPORARY TABLE' for thread
  creates one DROP TEMPORARY TABLE binlog event for each pseudo-thread.

  Temporary tables created in a sql slave is closed by
  Relay_log_info::close_temporary_tables().

  @return false                       Success
          true                        Failure
*/
bool THD::close_temporary_tables()
{
  DBUG_ENTER("THD::close_temporary_tables");

  TMP_TABLE_SHARE *share;
  TABLE *table;

  bool error= false;

  if (!has_thd_temporary_tables())
  {
    if (temporary_tables)
    {
      my_free(temporary_tables);
      temporary_tables= NULL;
    }
    DBUG_RETURN(false);
  }

  DBUG_ASSERT(!rgi_slave);

  /*
    Ensure we don't have open HANDLERs for tables we are about to close.
    This is necessary when THD::close_temporary_tables() is called as
    part of execution of BINLOG statement (e.g. for format description event).
  */
  mysql_ha_rm_temporary_tables(this);

  /* Close all open temporary tables. */
  All_tmp_tables_list::Iterator it(*temporary_tables);
  while ((share= it++))
  {
    /* Traverse the table list. */
    while ((table= share->all_tmp_tables.pop_front()))
    {
      table->file->extra(HA_EXTRA_PREPARE_FOR_DROP);
      free_temporary_table(table);
    }
  }

  // Write DROP TEMPORARY TABLE query log events to binary log.
  if (mysql_bin_log.is_open())
  {
    error= log_events_and_free_tmp_shares();
  }
  else
  {
    while ((share= temporary_tables->pop_front()))
    {
      free_tmp_table_share(share, true);
    }
  }

  /* By now, there mustn't be any elements left in the list. */
  DBUG_ASSERT(temporary_tables->is_empty());

  my_free(temporary_tables);
  temporary_tables= NULL;

  DBUG_RETURN(error);
}


/**
  Rename a temporary table.

  @param table [IN]                   Table handle
  @param db [IN]                      New schema name
  @param table_name [IN]              New table name

  @return false                       Success
          true                        Error
*/
bool THD::rename_temporary_table(TABLE *table,
                                 const LEX_CSTRING *db,
                                 const LEX_CSTRING *table_name)
{
  char *key;
  uint key_length;
  TABLE_SHARE *share= table->s;
  DBUG_ENTER("THD::rename_temporary_table");

  if (!(key= (char *) alloc_root(&share->mem_root, MAX_DBKEY_LENGTH)))
    DBUG_RETURN(true);

  /*
    Temporary tables are renamed by simply changing their table definition key.
  */
  key_length= create_tmp_table_def_key(key, db->str, table_name->str);
  share->set_table_cache_key(key, key_length);

  DBUG_RETURN(false);
}


/**
  Drop a temporary table.

  Try to locate the table in the list of open temporary tables.
  If the table is found:
   - If the table is locked with LOCK TABLES or by prelocking,
     unlock it and remove it from the list of locked tables
     (THD::lock). Currently only transactional temporary tables
     are locked.
   - Close the temporary table, remove its .FRM.
   - Remove the table share from the list of temporary table shares.

  This function is used to drop user temporary tables, as well as
  internal tables created in CREATE TEMPORARY TABLE ... SELECT
  or ALTER TABLE.

  @param table [IN]                   Temporary table to be deleted
  @param is_trans [OUT]               Is set to the type of the table:
                                      transactional (e.g. innodb) as true or
                                      non-transactional (e.g. myisam) as false.
  @paral delete_table [IN]            Whether to delete the table files?

  @return false                       Table was dropped
          true                        Error
*/
bool THD::drop_temporary_table(TABLE *table, bool *is_trans, bool delete_table)
{
  DBUG_ENTER("THD::drop_temporary_table");

  TMP_TABLE_SHARE *share;
  TABLE *tab;
  bool result= false;
  bool locked;

  DBUG_ASSERT(table);
  DBUG_PRINT("tmptable", ("Dropping table: '%s'.'%s'",
                          table->s->db.str, table->s->table_name.str));

  // close all handlers in case it is statement abort and some can be left
  if (is_error())
    table->file->ha_reset();

  locked= lock_temporary_tables();

  share= tmp_table_share(table);

  /* Table might be in use by some outer statement. */
  All_share_tables_list::Iterator it(share->all_tmp_tables);
  while ((tab= it++))
  {
    if (tab != table && tab->query_id != 0)
    {
      /* Found a table instance in use. This table cannot be be dropped. */
      my_error(ER_CANT_REOPEN_TABLE, MYF(0), table->alias.c_ptr());
      result= true;
      goto end;
    }
  }

  if (is_trans)
    *is_trans= table->file->has_transactions();

  /*
    Iterate over the list of open tables and close them.
  */
  while ((tab= share->all_tmp_tables.pop_front()))
  {
    /*
      We need to set the THD as it may be different in case of
      parallel replication
    */
    tab->in_use= this;
    if (delete_table)
      tab->file->extra(HA_EXTRA_PREPARE_FOR_DROP);
    free_temporary_table(tab);
  }

  DBUG_ASSERT(temporary_tables);

  /* Remove the TABLE_SHARE from the list of temporary tables. */
  temporary_tables->remove(share);

  /* Free the TABLE_SHARE and/or delete the files. */
  result= free_tmp_table_share(share, delete_table);

end:
  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(result);
}


/**
  Delete the temporary table files.

  @param base [IN]                    Handlerton for table to be deleted.
  @param path [IN]                    Path to the table to be deleted (i.e. path
                                      to its .frm without an extension).

  @return false                       Success
          true                        Error
*/
bool THD::rm_temporary_table(handlerton *base, const char *path)
{
  DBUG_ENTER("THD::rm_temporary_table");

  bool error= false;
  char frm_path[FN_REFLEN + 1];

  strxnmov(frm_path, sizeof(frm_path) - 1, path, reg_ext, NullS);

  if (base->drop_table(base, path) > 0)
  {
    error= true;
    sql_print_warning("Could not remove temporary table: '%s', error: %d",
                      path, my_errno);
  }

  if (mysql_file_delete(key_file_frm, frm_path,
                        MYF(MY_WME | MY_IGNORE_ENOENT)))
    error= true;

  DBUG_RETURN(error);
}


/**
  Mark all temporary tables which were used by the current statement or
  sub-statement as free for reuse, but only if the query_id can be cleared.

  @remark For temp tables associated with a open SQL HANDLER the query_id
          is not reset until the HANDLER is closed.
*/
void THD::mark_tmp_tables_as_free_for_reuse()
{
  DBUG_ENTER("THD::mark_tmp_tables_as_free_for_reuse");

  TMP_TABLE_SHARE *share;
  TABLE *table;
  bool locked;

  if (query_id == 0)
  {
    /*
      Thread has not executed any statement and has not used any
      temporary tables.
    */
    DBUG_VOID_RETURN;
  }

  if (!has_temporary_tables())
  {
    DBUG_VOID_RETURN;
  }

  locked= lock_temporary_tables();

  All_tmp_tables_list::Iterator it(*temporary_tables);
  while ((share= it++))
  {
    All_share_tables_list::Iterator tables_it(share->all_tmp_tables);
    while ((table= tables_it++))
    {
      if ((table->query_id == query_id) && !table->open_by_handler)
        mark_tmp_table_as_free_for_reuse(table);
    }
  }

  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  if (rgi_slave)
  {
    /*
      Temporary tables are shared with other by sql execution threads.
      As a safety measure, clear the pointer to the common area.
    */
    temporary_tables= NULL;
  }

  DBUG_VOID_RETURN;
}


/**
  Reset a single temporary table. Effectively this "closes" one temporary
  table in a session.

  @param table              Temporary table

  @return void
*/
void THD::mark_tmp_table_as_free_for_reuse(TABLE *table)
{
  DBUG_ENTER("THD::mark_tmp_table_as_free_for_reuse");

  DBUG_ASSERT(table->s->tmp_table);

  table->query_id= 0;
  table->file->ha_reset();

  /* Detach temporary MERGE children from temporary parent. */
  DBUG_ASSERT(table->file);
  table->file->extra(HA_EXTRA_DETACH_CHILDREN);

  /*
    Reset temporary table lock type to it's default value (TL_WRITE).

    Statements such as INSERT INTO .. SELECT FROM tmp, CREATE TABLE
    .. SELECT FROM tmp and UPDATE may under some circumstances modify
    the lock type of the tables participating in the statement. This
    isn't a problem for non-temporary tables since their lock type is
    reset at every open, but the same does not occur for temporary
    tables for historical reasons.

    Furthermore, the lock type of temporary tables is not really that
    important because they can only be used by one query at a time.
    Nonetheless, it's safer from a maintenance point of view to reset
    the lock type of this singleton TABLE object as to not cause problems
    when the table is reused.

    Even under LOCK TABLES mode its okay to reset the lock type as
    LOCK TABLES is allowed (but ignored) for a temporary table.
  */
  table->reginfo.lock_type= TL_WRITE;
  DBUG_VOID_RETURN;
}


/**
  Remove and return the specified table's TABLE_SHARE from the temporary
  tables list.

  @param table [IN]                   Table

  @return TMP_TABLE_SHARE of the specified table.
*/
TMP_TABLE_SHARE *THD::save_tmp_table_share(TABLE *table)
{
  DBUG_ENTER("THD::save_tmp_table_share");

  TMP_TABLE_SHARE *share;

  lock_temporary_tables();
  DBUG_ASSERT(temporary_tables);
  share= tmp_table_share(table);
  temporary_tables->remove(share);
  unlock_temporary_tables();

  DBUG_RETURN(share);
}


/**
  Add the specified TMP_TABLE_SHARE to the temporary tables list.

  @param share [IN]                   Table share

  @return void
*/
void THD::restore_tmp_table_share(TMP_TABLE_SHARE *share)
{
  DBUG_ENTER("THD::restore_tmp_table_share");

  lock_temporary_tables();
  DBUG_ASSERT(temporary_tables);
  temporary_tables->push_front(share);
  unlock_temporary_tables();

  DBUG_VOID_RETURN;
}


/**
  If its a replication slave, report whether slave temporary tables
  exist (Relay_log_info::save_temporary_tables) or report about THD
  temporary table (Open_tables_state::temporary_tables) otherwise.

  @return false                       Temporary tables exist
          true                        No temporary table exist
*/
bool THD::has_temporary_tables()
{
  DBUG_ENTER("THD::has_temporary_tables");
  bool result;
#ifdef HAVE_REPLICATION
  if (rgi_slave)
  {
    mysql_mutex_lock(&rgi_slave->rli->data_lock);
    result= rgi_slave->rli->save_temporary_tables &&
      !rgi_slave->rli->save_temporary_tables->is_empty();
    mysql_mutex_unlock(&rgi_slave->rli->data_lock);
  }
  else
#endif
  {
    result= has_thd_temporary_tables();
  }
  DBUG_RETURN(result);
}


/**
  Create a table definition key.

  @param key [OUT]                    Buffer for the key to be created (must
                                      be of size MAX_DBKRY_LENGTH)
  @param db [IN]                      Database name
  @param table_name [IN]              Table name

  @return                             Key length.

  @note
    The table key is create from:
    db + \0
    table_name + \0

    Additionally, we add the following to make each temporary table unique on
    the slave.

    4 bytes of master thread id
    4 bytes of pseudo thread id
*/
uint THD::create_tmp_table_def_key(char *key, const char *db,
                                    const char *table_name)
{
  uint key_length;
  DBUG_ENTER("THD::create_tmp_table_def_key");

  key_length= tdc_create_key(key, db, table_name);
  int4store(key + key_length, variables.server_id);
  int4store(key + key_length + 4, variables.pseudo_thread_id);
  key_length += TMP_TABLE_KEY_EXTRA;

  DBUG_RETURN(key_length);
}


/**
  Create a temporary table.

  @param frm  [IN]                    Binary frm image
  @param path [IN]                    File path (without extension)
  @param db   [IN]                    Schema name
  @param table_name [IN]              Table name

  @return Success                     A pointer to table share object
          Failure                     NULL
*/
TMP_TABLE_SHARE *THD::create_temporary_table(LEX_CUSTRING *frm,
                                             const char *path,
                                             const char *db,
                                             const char *table_name)
{
  DBUG_ENTER("THD::create_temporary_table");

  TMP_TABLE_SHARE *share;
  char key_cache[MAX_DBKEY_LENGTH];
  char *saved_key_cache;
  char *tmp_path;
  uint key_length;
  bool locked;
  int res;

  /* Temporary tables are not safe for parallel replication. */
  if (rgi_slave &&
      rgi_slave->is_parallel_exec &&
      wait_for_prior_commit())
    DBUG_RETURN(NULL);

  /* Create the table definition key for the temporary table. */
  key_length= create_tmp_table_def_key(key_cache, db, table_name);

  if (!(share= (TMP_TABLE_SHARE *) my_malloc(key_memory_table_share,
                                             sizeof(TMP_TABLE_SHARE) +
                                             strlen(path) + 1 + key_length,
                                             MYF(MY_WME))))
  {
    DBUG_RETURN(NULL);                          /* Out of memory */
  }

  tmp_path= (char *)(share + 1);
  saved_key_cache= strmov(tmp_path, path) + 1;
  memcpy(saved_key_cache, key_cache, key_length);

  init_tmp_table_share(this, share, saved_key_cache, key_length,
                       strend(saved_key_cache) + 1, tmp_path);

  /*
    Prefer using frm image over file. The image might not be available in
    ALTER TABLE, when the discovering engine took over the ownership (see
    TABLE::read_frm_image).
  */
  res= (frm->str)
    ? share->init_from_binary_frm_image(this, false, frm->str, frm->length)
    : open_table_def(this, share, GTS_TABLE | GTS_USE_DISCOVERY);

  if (res)
  {
    /*
      No need to lock share->mutex as this is not needed for temporary tables.
    */
    free_table_share(share);
    my_free(share);
    DBUG_RETURN(NULL);
  }

  share->m_psi= PSI_CALL_get_table_share(true, share);

  locked= lock_temporary_tables();

  /* Initialize the all_tmp_tables list. */
  share->all_tmp_tables.empty();

  /*
    We need to alloc & initialize temporary_tables if this happens
    to be the very first temporary table.
  */
  if (!temporary_tables)
  {
    if ((temporary_tables=
         (All_tmp_tables_list *) my_malloc(key_memory_table_share,
                                           sizeof(All_tmp_tables_list),
                                           MYF(MY_WME))))
    {
      temporary_tables->empty();
    }
    else
    {
      DBUG_RETURN(NULL);                        /* Out of memory */
    }
  }

  /* Add share to the head of the temporary table share list. */
  temporary_tables->push_front(share);

  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(share);
}


/**
  Find a table with the specified key.

  @param key [IN]                     Key
  @param key_length [IN]              Key length
  @param state [IN]                   Open table state to look for

  @return Success                     Pointer to the table instance.
          Failure                     NULL
*/
TABLE *THD::find_temporary_table(const char *key, uint key_length,
                                 Temporary_table_state state)
{
  DBUG_ENTER("THD::find_temporary_table");

  TMP_TABLE_SHARE *share;
  TABLE *table;
  TABLE *result= NULL;
  bool locked;

  locked= lock_temporary_tables();

  All_tmp_tables_list::Iterator it(*temporary_tables);
  while ((share= it++))
  {
    if (share->table_cache_key.length == key_length &&
        !(memcmp(share->table_cache_key.str, key, key_length)))
    {
      /* A matching TMP_TABLE_SHARE is found. */
      All_share_tables_list::Iterator tables_it(share->all_tmp_tables);

      bool found= false;
      while (!found && (table= tables_it++))
      {
        switch (state)
        {
        case TMP_TABLE_IN_USE:     found= table->query_id > 0;  break;
        case TMP_TABLE_NOT_IN_USE: found= table->query_id == 0; break;
        case TMP_TABLE_ANY:        found= true;                 break;
        }
      }
      if (table && unlikely(table->needs_reopen()))
      {
        share->all_tmp_tables.remove(table);
        free_temporary_table(table);
        it.rewind();
        continue;
      }
      result= table;
      break;
    }
  }

  if (locked)
  {
    DBUG_ASSERT(m_tmp_tables_locked);
    unlock_temporary_tables();
  }

  DBUG_RETURN(result);
}



/**
  Open a table from the specified TABLE_SHARE with the given alias.

  @param share [IN]                   Table share
  @param alias [IN]                   Table alias

  @return Success                     A pointer to table object
          Failure                     NULL
*/
TABLE *THD::open_temporary_table(TMP_TABLE_SHARE *share,
                                 const char *alias_arg)
{
  TABLE *table;
  LEX_CSTRING alias= {alias_arg, strlen(alias_arg) };
  DBUG_ENTER("THD::open_temporary_table");


  if (!(table= (TABLE *) my_malloc(key_memory_TABLE, sizeof(TABLE),
                                   MYF(MY_WME))))
  {
    DBUG_RETURN(NULL);                          /* Out of memory */
  }

  uint flags= ha_open_options | (open_options & HA_OPEN_FOR_CREATE);
  /*
    In replication, temporary tables are not confined to a single
    thread/THD.
  */
  if (slave_thread)
    flags|= HA_OPEN_GLOBAL_TMP_TABLE;
  if (open_table_from_share(this, share, &alias,
                            (uint) HA_OPEN_KEYFILE,
                            EXTRA_RECORD, flags,
                            table, false))
  {
    my_free(table);
    DBUG_RETURN(NULL);
  }

  table->reginfo.lock_type= TL_WRITE;           /* Simulate locked */
  table->grant.privilege= TMP_TABLE_ACLS;
  table->query_id= query_id;
  share->tmp_table= (table->file->has_transaction_manager() ?
                     TRANSACTIONAL_TMP_TABLE : NON_TRANSACTIONAL_TMP_TABLE);
  share->not_usable_by_query_cache= 1;

  /* Add table to the head of table list. */
  share->all_tmp_tables.push_front(table);

  /* Increment Slave_open_temp_table_definitions status variable count. */
  if (rgi_slave)
    slave_open_temp_tables++;

  DBUG_PRINT("tmptable", ("Opened table: '%s'.'%s  table: %p",
                          table->s->db.str,
                          table->s->table_name.str, table));
  DBUG_RETURN(table);
}


/**
  Find a reusable table in the open table list using the specified TABLE_LIST.

  @param tl [IN]                      Table list
  @param out_table [OUT]              Pointer to the requested TABLE object

  @return Success                     false
          Failure                     true
*/
bool THD::find_and_use_tmp_table(const TABLE_LIST *tl, TABLE **out_table)
{
  char key[MAX_DBKEY_LENGTH];
  uint key_length;
  bool result;
  DBUG_ENTER("THD::find_and_use_tmp_table");

  key_length= create_tmp_table_def_key(key, tl->get_db_name().str,
                                        tl->get_table_name().str);
  result= use_temporary_table(find_temporary_table(key, key_length,
                                                   TMP_TABLE_NOT_IN_USE),
                              out_table);
  DBUG_RETURN(result);
}

/**
  Mark table as in-use.

  @param table [IN]                   Table to be marked in-use
  @param out_table [OUT]              Pointer to the specified table

  @return false                       Success
          true                        Error
*/
bool THD::use_temporary_table(TABLE *table, TABLE **out_table)
{
  DBUG_ENTER("THD::use_temporary_table");

  *out_table= table;

  /* The following can happen if find_temporary_table() returns NULL */
  if (!table)
    DBUG_RETURN(false);

  /*
    Temporary tables are not safe for parallel replication. They were
    designed to be visible to one thread only, so have no table locking.
    Thus there is no protection against two conflicting transactions
    committing in parallel and things like that.

    So for now, anything that uses temporary tables will be serialised
    with anything before it, when using parallel replication.

    TODO: We might be able to introduce a reference count or something
    on temp tables, and have slave worker threads wait for it to reach
    zero before being allowed to use the temp table. Might not be worth
    it though, as statement-based replication using temporary tables is
    in any case rather fragile.
  */
  if (rgi_slave &&
      rgi_slave->is_parallel_exec &&
      wait_for_prior_commit())
    DBUG_RETURN(true);

  /*
    We need to set the THD as it may be different in case of
    parallel replication
  */
  table->in_use= this;

  DBUG_RETURN(false);
}


/**
  Close a temporary table.

  @param table [IN]                   Table handle

  @return void
*/
void THD::close_temporary_table(TABLE *table)
{
  DBUG_ENTER("THD::close_temporary_table");

  DBUG_PRINT("tmptable", ("closing table: '%s'.'%s'%p  alias: '%s'",
                          table->s->db.str, table->s->table_name.str,
                          table, table->alias.c_ptr()));

  closefrm(table);
  my_free(table);

  if (rgi_slave)
  {
    /* Natural invariant of temporary_tables */
    DBUG_ASSERT(slave_open_temp_tables || !temporary_tables);
    /* Decrement Slave_open_temp_table_definitions status variable count. */
    slave_open_temp_tables--;
  }

  DBUG_VOID_RETURN;
}


/**
  Write query log events with "DROP TEMPORARY TABLES .." for each pseudo
  thread to the binary log.

  @return false                       Success
          true                        Error
*/
bool THD::log_events_and_free_tmp_shares()
{
  DBUG_ENTER("THD::log_events_and_free_tmp_shares");

  DBUG_ASSERT(!rgi_slave);

  TMP_TABLE_SHARE *share;
  TMP_TABLE_SHARE *sorted;
  TMP_TABLE_SHARE *prev_sorted;
  // Assume thd->variables.option_bits has OPTION_QUOTE_SHOW_CREATE.
  bool was_quote_show= true;
  bool error= false;
  bool found_user_tables= false;
  // Better add "IF EXISTS" in case a RESET MASTER has been done.
  const char stub[]= "DROP /*!40005 TEMPORARY */ TABLE IF EXISTS ";
  char buf[FN_REFLEN];

  String s_query(buf, sizeof(buf), system_charset_info);
  s_query.copy(stub, sizeof(stub) - 1, system_charset_info);

  /*
    Insertion sort of temporary tables by pseudo_thread_id to build ordered
    list of sublists of equal pseudo_thread_id.
  */
  All_tmp_tables_list::Iterator it_sorted(*temporary_tables);
  All_tmp_tables_list::Iterator it_unsorted(*temporary_tables);
  uint sorted_count= 0;
  while((share= it_unsorted++))
  {
    if (IS_USER_TABLE(share))
    {
      prev_sorted= NULL;

      if (!found_user_tables) found_user_tables= true;

      for (uint i= 0; i < sorted_count; i ++)
      {
        sorted= it_sorted ++;

        if (!IS_USER_TABLE(sorted) ||
            (tmpkeyval(sorted) > tmpkeyval(share)))
        {
          /*
            Insert this share before the current element in
            the sorted part of the list.
          */
          temporary_tables->remove(share);

          if (prev_sorted)
          {
            temporary_tables->insert_after(prev_sorted, share);
          }
          else
          {
            temporary_tables->push_front(share);
          }
          break;
        }
        prev_sorted= sorted;
      }
      it_sorted.rewind();
    }
    sorted_count ++;
  }

  /*
    We always quote db & table names.
  */
  if (found_user_tables &&
      !(was_quote_show= MY_TEST(variables.option_bits &
                                OPTION_QUOTE_SHOW_CREATE)))
  {
    variables.option_bits |= OPTION_QUOTE_SHOW_CREATE;
  }

  /*
    Scan sorted temporary tables to generate sequence of DROP.
  */
  share= temporary_tables->pop_front();
  while (share)
  {
    if (IS_USER_TABLE(share))
    {
      used_t save_thread_specific_used= used & THREAD_SPECIFIC_USED;
      my_thread_id save_pseudo_thread_id= variables.pseudo_thread_id;
      char db_buf[FN_REFLEN];
      String db(db_buf, sizeof(db_buf), system_charset_info);
      bool at_least_one_create_logged;

      /*
        Set pseudo_thread_id to be that of the processed table.
      */
      variables.pseudo_thread_id= tmpkeyval(share);

      db.copy(share->db.str, share->db.length, system_charset_info);
      /*
        Reset s_query() if changed by previous loop.
      */
      s_query.length(sizeof(stub) - 1);

      /*
        Loop forward through all tables that belong to a common database
        within the sublist of common pseudo_thread_id to create single
        DROP query.
      */
      for (at_least_one_create_logged= false;
           share && IS_USER_TABLE(share) &&
           tmpkeyval(share) == variables.pseudo_thread_id &&
           share->db.length == db.length() &&
           memcmp(share->db.str, db.ptr(), db.length()) == 0;
           /* Get the next TABLE_SHARE in the list. */
           share= temporary_tables->pop_front())
      {
        if (share->table_creation_was_logged)
        {
          at_least_one_create_logged= true;
          /*
             We are going to add ` around the table names and possible more
             due to special characters.
          */
          append_identifier(this, &s_query, &share->table_name);
          s_query.append(',');
        }
        rm_temporary_table(share->db_type(), share->path.str);
        free_table_share(share);
        my_free(share);
      }

      if (at_least_one_create_logged)
      {
        clear_error();
        CHARSET_INFO *cs_save= variables.character_set_client;
        variables.character_set_client= system_charset_info;
        used|= THREAD_SPECIFIC_USED;

        Query_log_event qinfo(this, s_query.ptr(),
            s_query.length() - 1 /* to remove trailing ',' */,
            false, true, false, 0);
        qinfo.db= db.ptr();
        qinfo.db_len= db.length();
        variables.character_set_client= cs_save;

        get_stmt_da()->set_overwrite_status(true);
        transaction->stmt.mark_dropped_temp_table();
        bool error2= mysql_bin_log.write(&qinfo);
        if (unlikely(error|= error2))
        {
          /*
             If we're here following THD::cleanup, thence the connection
             has been closed already. So lets print a message to the
             error log instead of pushing yet another error into the
             stmt_da.

             Also, we keep the error flag so that we propagate the error
             up in the stack. This way, if we're the SQL thread we notice
             that THD::close_tables failed. (Actually, the SQL
             thread only calls THD::close_tables while applying
             old Start_log_event_v3 events.)
          */
          sql_print_error("Failed to write the DROP statement for "
              "temporary tables to binary log");
        }

        get_stmt_da()->set_overwrite_status(false);
      }
      variables.pseudo_thread_id= save_pseudo_thread_id;
      used = (used & ~THREAD_SPECIFIC_USED) | save_thread_specific_used;
    }
    else
    {
      free_tmp_table_share(share, true);
      /* Get the next TABLE_SHARE in the list. */
      share= temporary_tables->pop_front();
    }
  }

  if (!was_quote_show)
  {
    /*
      Restore option.
    */
    variables.option_bits&= ~OPTION_QUOTE_SHOW_CREATE;
  }

  DBUG_RETURN(error);
}


/**
  Delete the files and free the specified table share.

  @param share [IN]                   TABLE_SHARE to free
  @param delete_table [IN]            Whether to delete the table files?

  @return false                       Success
          true                        Error
*/
bool THD::free_tmp_table_share(TMP_TABLE_SHARE *share, bool delete_table)
{
  bool error= false;
  DBUG_ENTER("THD::free_tmp_table_share");

  if (delete_table)
  {
    error= rm_temporary_table(share->db_type(), share->path.str);
  }
  free_table_share(share);
  my_free(share);
  DBUG_RETURN(error);
}


/**
  Free the specified table object.

  @param table [IN]                   Table object to free.

  @return void
*/
void THD::free_temporary_table(TABLE *table)
{
  DBUG_ENTER("THD::free_temporary_table");

  /*
    If LOCK TABLES list is not empty and contains this table, unlock the table
    and remove the table from this list.
  */
  mysql_lock_remove(this, lock, table);

  close_temporary_table(table);

  DBUG_VOID_RETURN;
}


/**
  On replication slave, acquire the Relay_log_info's data_lock and use slave
  temporary tables.

  @return true                        Lock acquired
          false                       Lock wasn't acquired
*/
bool THD::lock_temporary_tables()
{
  DBUG_ENTER("THD::lock_temporary_tables");

  /* Do not proceed if a lock has already been taken. */
  if (m_tmp_tables_locked)
  {
    DBUG_RETURN(false);
  }

#ifdef HAVE_REPLICATION
  if (rgi_slave)
  {
    mysql_mutex_lock(&rgi_slave->rli->data_lock);
    temporary_tables= rgi_slave->rli->save_temporary_tables;
    m_tmp_tables_locked= true;
  }
#endif

  DBUG_RETURN(m_tmp_tables_locked);
}


/**
  On replication slave, release the Relay_log_info::data_lock previously
  acquired to use slave temporary tables.

  @return void
*/
void THD::unlock_temporary_tables()
{
  DBUG_ENTER("THD::unlock_temporary_tables");

  if (!m_tmp_tables_locked)
  {
    DBUG_VOID_RETURN;
  }

#ifdef HAVE_REPLICATION
  if (rgi_slave)
  {
    rgi_slave->rli->save_temporary_tables= temporary_tables;
    temporary_tables= NULL;                     /* Safety */
    mysql_mutex_unlock(&rgi_slave->rli->data_lock);
    m_tmp_tables_locked= false;
  }
#endif

  DBUG_VOID_RETURN;
}


/**
  Close unused TABLE instances for given temporary table.

  @param tl [IN]                      TABLE_LIST

  Initial use case was TRUNCATE, which expects only one instance (which is used
  by TRUNCATE itself) to be open. Most probably some ALTER TABLE variants and
  REPAIR may have similar expectations.
*/

void THD::close_unused_temporary_table_instances(const TABLE_LIST *tl)
{
  TMP_TABLE_SHARE *share= find_tmp_table_share(tl);

  if (share)
  {
    All_share_tables_list::Iterator tables_it(share->all_tmp_tables);

     while (TABLE *table= tables_it++)
     {
       if (table->query_id == 0)
       {
         /* Note: removing current list element doesn't invalidate iterator. */
         share->all_tmp_tables.remove(table);
         /*
           At least one instance should be left (guaratead by calling this
           function for table which is opened and the table is under processing)
         */
         DBUG_ASSERT(share->all_tmp_tables.front());
         free_temporary_table(table);
       }
     }
  }
}