Method lock_table

sql/sql_truncate.cc:299–606

*/

bool Sql_cmd_truncate_table::lock_table(THD *thd, TABLE_LIST *table_ref,
                                        bool *hton_can_recreate)
{
  const handlerton *hton;
  bool versioned;
  bool sequence= false;
  TABLE *table= NULL;
  DBUG_ENTER("Sql_cmd_truncate_table::lock_table");

  /* Lock types are set in the parser. */
  DBUG_ASSERT(table_ref->lock_type == TL_WRITE);
  /* The handler truncate protocol dictates a exclusive lock. */
  DBUG_ASSERT(table_ref->mdl_request.type == MDL_EXCLUSIVE);

  /*
    Before doing anything else, acquire a metadata lock on the table,
    or ensure we have one.  We don't use open_and_lock_tables()
    right away because we want to be able to truncate (and recreate)
    corrupted tables, those that we can't fully open.

    MySQL manual documents that TRUNCATE can be used to repair a
    damaged table, i.e. a table that can not be fully "opened".
    In particular MySQL manual says: As long as the table format
    file tbl_name.frm is valid, the table can be re-created as
    an empty table with TRUNCATE TABLE, even if the data or index
    files have become corrupted.
  */
  if (thd->locked_tables_mode)
  {
    if (!(table= find_table_for_mdl_upgrade(thd, table_ref->db.str,
                                            table_ref->table_name.str, NULL)))
      DBUG_RETURN(TRUE);

    versioned= table->versioned();
    hton= table->file->ht;
#ifdef WITH_WSREP
    /* Resolve should we replicate truncate. It should
       be replicated if storage engine(s) associated
       are replicated by Galera. If this is partitioned
       table we need to find out default partition
       handlerton.
    */
    if (WSREP(thd) &&
        !wsrep_should_replicate_ddl(thd, table->file->partition_ht() ?
                                    table->file->partition_ht() : hton))
      DBUG_RETURN(TRUE);
#endif

    table_ref->mdl_request.ticket= table->mdl_ticket;
  }
  else
  {
    DBUG_ASSERT(table_ref->next_global == NULL);
    if (lock_table_names(thd, table_ref, NULL,
                         thd->variables.lock_wait_timeout, 0))
      DBUG_RETURN(TRUE);

    TABLE_SHARE *share= tdc_acquire_share(thd, table_ref, GTS_TABLE | GTS_VIEW);