diff options
Diffstat (limited to 'sql/sql_show.cc')
| -rw-r--r-- | sql/sql_show.cc | 33 |
1 files changed, 28 insertions, 5 deletions
diff --git a/sql/sql_show.cc b/sql/sql_show.cc index 4485991cdaf..a65a2e40577 100644 --- a/sql/sql_show.cc +++ b/sql/sql_show.cc @@ -3573,6 +3573,10 @@ end: */ thd->temporary_tables= NULL; close_thread_tables(thd); + /* + Release metadata lock we might have acquired. + See comment in fill_schema_table_from_frm() for details. + */ thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp); thd->lex= old_lex; @@ -3755,6 +3759,9 @@ try_acquire_high_prio_shared_mdl_lock(THD *thd, TABLE_LIST *table, @param[in] db_name database name @param[in] table_name table name @param[in] schema_table_idx I_S table index + @param[in] open_tables_state_backup Open_tables_state object which is used + to save/restore original state of metadata + locks. @param[in] can_deadlock Indicates that deadlocks are possible due to metadata locks, so to avoid them we should not wait in case if @@ -3772,6 +3779,7 @@ static int fill_schema_table_from_frm(THD *thd, TABLE_LIST *tables, LEX_STRING *db_name, LEX_STRING *table_name, enum enum_schema_tables schema_table_idx, + Open_tables_backup *open_tables_state_backup, bool can_deadlock) { TABLE *table= tables->table; @@ -3916,13 +3924,27 @@ end_share: end_unlock: mysql_mutex_unlock(&LOCK_open); - /* - Don't release the MDL lock, it can be part of a transaction. - If it is not, it will be released by the call to - MDL_context::rollback_to_savepoint() in the caller. - */ end: + /* + Release metadata lock we might have acquired. + + Without this step metadata locks acquired for each table processed + will be accumulated. In situation when a lot of tables are processed + by I_S query this will result in transaction with too many metadata + locks. As result performance of acquisition of new lock will suffer. + + Of course, the fact that we don't hold metadata lock on tables which + were processed till the end of I_S query makes execution less isolated + from concurrent DDL. Consequently one might get 'dirty' results from + such a query. But we have never promised serializability of I_S queries + anyway. + + We don't have any tables open since we took backup, so rolling back to + savepoint is safe. + */ + DBUG_ASSERT(thd->open_tables == NULL); + thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp); thd->clear_error(); return res; } @@ -4173,6 +4195,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond) int res= fill_schema_table_from_frm(thd, tables, schema_table, db_name, table_name, schema_table_idx, + &open_tables_state_backup, can_deadlock); thd->pop_internal_handler(); |