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Bug #54332 Deadlock with two connections doing LOCK TABLE+INSERT DELAYED

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The problem was that deadlocks involving INSERT DELAYED were not detected.

The reason for this is that two threads are involved in INSERT DELAYED:
the connection thread and the handler thread. The connection thread would
wait while the handler thread acquired locks and opened the table.
In essence, this adds an edge to the wait-for-graph between the 
connection thread and the handler thread that the deadlock detector is
unaware of. Therefore many deadlocks involving INSERT DELAYED were not 
detected.

This patch fixes the problem by having the connection thread acquire the
metadata lock the table before starting the handler thread. This allows the
deadlock detector to detect any possible deadlocks resulting from trying to
acquire a metadata lock the table. If a metadata lock is successfully acquired,
the handler thread is started and given a copy of the ticket representing the
metadata lock. When the handler thread then tries to lock and open the table,
it will find that it already has the metadata lock and therefore not acquire
any new metadata locks.

Test cases added to delayed.test.
This commit is contained in:
Jon Olav Hauglid
2010-08-23 17:42:53 +02:00
parent 258d892896
commit 3592489cae
3 changed files with 297 additions and 10 deletions
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73
sql/sql_insert.cc
View File

@ -548,10 +548,34 @@ bool open_and_lock_for_insert_delayed(THD *thd, TABLE_LIST *table_list)
DBUG_RETURN(TRUE);
}
if (delayed_get_table(thd, table_list))
/*
In order for the deadlock detector to be able to find any deadlocks
caused by the handler thread locking this table, we take the metadata
lock inside the connection thread. If this goes ok, the ticket is cloned
and added to the list of granted locks held by the handler thread.
*/
MDL_ticket *mdl_savepoint= thd->mdl_context.mdl_savepoint();
if (thd->mdl_context.acquire_lock(&table_list->mdl_request,
thd->variables.lock_wait_timeout))
/*
If a lock can't be acquired, it makes no sense to try normal insert.
Therefore we just abort the statement.
*/
DBUG_RETURN(TRUE);
if (table_list->table)
/*
If a lock was acquired above, we should release it after delayed_get_table()
has cloned the ticket for the handler thread. Note that acquire_lock() can
succeed because of a lock already held by the connection. In this case we
should not release it here.
*/
MDL_ticket *table_ticket = mdl_savepoint == thd->mdl_context.mdl_savepoint() ?
NULL: thd->mdl_context.mdl_savepoint();
bool error= FALSE;
if (delayed_get_table(thd, table_list))
error= TRUE;
else if (table_list->table)
{
/*
Open tables used for sub-selects or in stored functions, will also
@ -560,16 +584,30 @@ bool open_and_lock_for_insert_delayed(THD *thd, TABLE_LIST *table_list)
if (open_and_lock_tables(thd, table_list->next_global, TRUE, 0))
{
end_delayed_insert(thd);
DBUG_RETURN(TRUE);
error= TRUE;
}
else
{
/*
First table was not processed by open_and_lock_tables(),
we need to set updatability flag "by hand".
*/
if (!table_list->derived && !table_list->view)
table_list->updatable= 1; // usual table
}
/*
First table was not processed by open_and_lock_tables(),
we need to set updatability flag "by hand".
*/
if (!table_list->derived && !table_list->view)
table_list->updatable= 1; // usual table
DBUG_RETURN(FALSE);
}
if (table_ticket)
thd->mdl_context.release_lock(table_ticket);
/*
Clone_ticket() in delayed_get_table() causes TABLE_LIST::MDL_REQUEST::ticket
to be overwritten with the cloned ticket. Reset the ticket here in case
we end up having to use normal insert.
*/
table_list->mdl_request.ticket= NULL;
if (error || table_list->table)
DBUG_RETURN(error);
#endif
/*
* This is embedded library and we don't have auxiliary
@ -2025,6 +2063,20 @@ bool delayed_get_table(THD *thd, TABLE_LIST *table_list)
/* Replace volatile strings with local copies */
di->table_list.alias= di->table_list.table_name= di->thd.query();
di->table_list.db= di->thd.db;
/*
Clone the ticket representing the lock on the target table for
the insert and add it to the list of granted metadata locks held by
the handler thread. This is safe since the handler thread is
not holding nor waiting on any metadata locks.
*/
if (di->thd.mdl_context.clone_ticket(&table_list->mdl_request))
{
delete di;
my_error(ER_OUT_OF_RESOURCES, MYF(ME_FATALERROR));
goto end_create;
}
di->lock();
mysql_mutex_lock(&di->mutex);
if ((error= mysql_thread_create(key_thread_delayed_insert,
@ -2036,6 +2088,7 @@ bool delayed_get_table(THD *thd, TABLE_LIST *table_list)
error));
mysql_mutex_unlock(&di->mutex);
di->unlock();
di->thd.mdl_context.release_lock(table_list->mdl_request.ticket);
delete di;
my_error(ER_CANT_CREATE_THREAD, MYF(ME_FATALERROR), error);
goto end_create;