Method handler_truncate

sql/sql_truncate.cc:185–283

*/

enum Sql_cmd_truncate_table::truncate_result
Sql_cmd_truncate_table::handler_truncate(THD *thd, TABLE_LIST *table_ref,
                                         bool is_tmp_table)
{
  int error= 0;
  uint flags= 0;
  TABLE *table;
  DBUG_ENTER("Sql_cmd_truncate_table::handler_truncate");

  /*
    Can't recreate, the engine must mechanically delete all rows
    in the table. Use open_and_lock_tables() to open a write cursor.
  */

  /* If it is a temporary table, no need to take locks. */
  if (!is_tmp_table)
  {
    /* We don't need to load triggers. */
    DBUG_ASSERT(table_ref->trg_event_map == 0);
    /*
      Our metadata lock guarantees that no transaction is reading
      or writing into the table. Yet, to open a write cursor we need
      a thr_lock lock. Allow to open base tables only.
    */
    table_ref->required_type= TABLE_TYPE_NORMAL;
    /*
      Ignore pending FLUSH TABLES since we don't want to release
      the MDL lock taken above and otherwise there is no way to
      wait for FLUSH TABLES in deadlock-free fashion.
    */
    flags= MYSQL_OPEN_IGNORE_FLUSH;
    /*
      Even though we have an MDL lock on the table here, we don't
      pass MYSQL_OPEN_HAS_MDL_LOCK to open_and_lock_tables
      since to truncate a MERGE table, we must open and lock
      merge children, and on those we don't have an MDL lock.
      Thus clear the ticket to satisfy MDL asserts.
    */
    table_ref->mdl_request.ticket= NULL;
  }

  /* Open the table as it will handle some required preparations. */
  if (open_and_lock_tables(thd, table_ref, FALSE, flags))
    DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);

  /* Whether to truncate regardless of foreign keys. */
  if (! (thd->variables.option_bits & OPTION_NO_FOREIGN_KEY_CHECKS))
    if (fk_truncate_illegal_if_parent(thd, table_ref->table))
      DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);

  table= table_ref->table;

  if ((table->file->ht->flags & HTON_TRUNCATE_REQUIRES_EXCLUSIVE_USE) &&
      !is_tmp_table)
  {
    if (wait_while_table_is_used(thd, table, HA_EXTRA_FORCE_REOPEN))
      DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);
    /*