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Patch that changes metadata locking subsystem to use mutex per lock and

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condition variable per context instead of one mutex and one conditional
variable for the whole subsystem.

This should increase concurrency in this subsystem.

It also opens the way for further changes which are necessary to solve
such bugs as bug #46272 "MySQL 5.4.4, new MDL: unnecessary deadlock"
and bug #37346 "innodb does not detect deadlock between update and alter
table".

Two other notable changes done by this patch:

- MDL subsystem no longer implicitly acquires global intention exclusive
  metadata lock when per-object metadata lock is acquired. Now this has
  to be done by explicit calls outside of MDL subsystem.
- Instead of using separate MDL_context for opening system tables/tables
  for purposes of I_S we now create MDL savepoint in the main context
  before opening tables and rollback to this savepoint after closing
  them. This means that it is now possible to get ER_LOCK_DEADLOCK error
  even not inside a transaction. This might happen in unlikely case when
  one runs DDL on one of system tables while also running DDL on some
  other tables. Cases when this ER_LOCK_DEADLOCK error is not justified
  will be addressed by advanced deadlock detector for MDL subsystem which
  we plan to implement.
This commit is contained in:
Dmitry Lenev
2010-01-21 23:43:03 +03:00
parent c005126107
commit a63f8480db
24 changed files with 1595 additions and 848 deletions
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11
sql/sql_class.cc
View File

@ -471,6 +471,7 @@ THD::THD()
{
ulong tmp;
mdl_context.init(this);
/*
Pass nominal parameters to init_alloc_root only to ensure that
the destructor works OK in case of an error. The main_mem_root
@ -1007,7 +1008,8 @@ void THD::cleanup(void)
*/
DBUG_ASSERT(open_tables == NULL);
/* All HANDLERs must have been closed by now. */
DBUG_ASSERT(mdl_context.lt_or_ha_sentinel() == NULL);
DBUG_ASSERT(mdl_context.lt_or_ha_sentinel() == NULL ||
global_read_lock);
/*
Due to the above assert, this is guaranteed to release *all* in
this session.
@ -3024,19 +3026,21 @@ bool Security_context::user_matches(Security_context *them)
access to mysql.proc table to find definitions of stored routines.
****************************************************************************/
void THD::reset_n_backup_open_tables_state(Open_tables_state *backup)
void THD::reset_n_backup_open_tables_state(Open_tables_backup *backup)
{
DBUG_ENTER("reset_n_backup_open_tables_state");
backup->set_open_tables_state(this);
backup->mdl_system_tables_svp= mdl_context.mdl_savepoint();
reset_open_tables_state(this);
state_flags|= Open_tables_state::BACKUPS_AVAIL;
DBUG_VOID_RETURN;
}
void THD::restore_backup_open_tables_state(Open_tables_state *backup)
void THD::restore_backup_open_tables_state(Open_tables_backup *backup)
{
DBUG_ENTER("restore_backup_open_tables_state");
mdl_context.rollback_to_savepoint(backup->mdl_system_tables_svp);
/*
Before we will throw away current open tables state we want
to be sure that it was properly cleaned up.
@ -3046,7 +3050,6 @@ void THD::restore_backup_open_tables_state(Open_tables_state *backup)
lock == 0 &&
locked_tables_mode == LTM_NONE &&
m_reprepare_observer == NULL);
mdl_context.destroy();
set_open_tables_state(backup);
DBUG_VOID_RETURN;