Marko Mäkelä added a comment - 2021-07-21 05:35 The following patch has been used during some performance testing to remove the scalability bottleneck due to backup locks, so that we can better highlight scalability bottlenecks inside storage engines. diff --git a/sql/handler.cc b/sql/handler.cc index eb7b5b8..012ef20 100644 --- a/sql/handler.cc +++ b/sql/handler.cc @@ -1567,7 +1567,7 @@ int ha_commit_trans(THD *thd, bool all) DBUG_PRINT("info", ("is_real_trans: %d rw_trans: %d rw_ha_count: %d", is_real_trans, rw_trans, rw_ha_count));   - if (rw_trans) + if (0 && rw_trans) { /* Acquire a metadata lock which will ensure that COMMIT is blocked diff --git a/sql/sql_base.cc b/sql/sql_base.cc index c41e08e..f9e3f34 100644 --- a/sql/sql_base.cc +++ b/sql/sql_base.cc @@ -2100,7 +2100,7 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx) }   if (!(flags & MYSQL_OPEN_HAS_MDL_LOCK) && - table->s->table_category < TABLE_CATEGORY_INFORMATION) + table->s->table_category < TABLE_CATEGORY_INFORMATION && 0) { /* We are not under LOCK TABLES and going to acquire write-lock/

Marko Mäkelä added a comment - 2023-12-12 14:15 Possibly, this locking can be removed as part of implementing backup in the server process ( MDEV-14992 ).

Michael Widenius added a comment - 2024-12-17 07:27 - edited I do not think it is possible to remove the backup lock in ha_commit_trans. This lock is essential to ensure that we can get a consistent backup, in any scenario (as far as I know). As long we support external backup tools, we need to have it, even if we have in server backup. It is also needed the lock to be able to create a consistent snapshot of the server. The lock is also critically needed for binlogs. It would be nice to be able to 'know in advance' that a backup will take place so that we could ignore all backup locks when there will not be any lock for existing transactions. What could be possible be done is to have a flag that disables all the backup locks. When we do BACKUP STAGE START, we would then enable the lock and wait for all transactions that was started outside of the lock to complete before continue.