database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-12-24 11:21:21 +03:00
Code Activity

Bug #55498 SHOW CREATE TRIGGER takes wrong type of metadata lock

Browse Source 
The first problem was that SHOW CREATE TRIGGER took a stronger metadata
lock than required. This caused the statement to be blocked when it was
not needed. For example, LOCK TABLE WRITE in one connection would block
SHOW CREATE TRIGGER in another connection.

Another problem was that a SHOW CREATE TRIGGER statement issued inside
a transaction did not release its metadata locks at the end of the
statement execution. This happened even if SHOW CREATE TRIGGER is an
information statement. The consequence was that SHOW CREATE TRIGGER
was able to block other connections from accessing the table
(e.g. using ALTER TABLE).

This patch fixes the problem by changing SHOW CREATE TRIGGER to take
a MDL_SHARED_HIGH_PRIO metadata lock similar to what is already done
for SHOW CREATE TABLE. The patch also changes SHOW CREATE TRIGGER to
explicitly release any metadata locks taken by the statement after
it completes.

Test case added to show_check.test.
This commit is contained in:
Jon Olav Hauglid
2010-07-23 10:44:55 +02:00
parent 5f9de42e26
commit 54c5e7c88f
3 changed files with 97 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
sql/sql_show.cc
View File

@@ -7779,6 +7779,10 @@ TABLE_LIST *get_trigger_table(THD *thd, const sp_name *trg_name)
bool show_create_trigger(THD *thd, const sp_name *trg_name)
{
TABLE_LIST *lst= get_trigger_table(thd, trg_name);
uint num_tables; /* NOTE: unused, only to pass to open_tables(). */
Table_triggers_list *triggers;
int trigger_idx;
bool error= TRUE;
if (!lst)
return TRUE;
@@ -7790,35 +7794,35 @@ bool show_create_trigger(THD *thd, const sp_name *trg_name)
}
/*
Open the table by name in order to load Table_triggers_list object.
NOTE: there is race condition here -- the table can be dropped after
LOCK_open is released. It will be fixed later by acquiring shared
metadata lock on trigger or table name.
Metadata locks taken during SHOW CREATE TRIGGER should be released when
the statement completes as it is an information statement.
*/
MDL_ticket *mdl_savepoint= thd->mdl_context.mdl_savepoint();
uint num_tables; /* NOTE: unused, only to pass to open_tables(). */
if (open_tables(thd, &lst, &num_tables, 0))
/*
Open the table by name in order to load Table_triggers_list object.
*/
if (open_tables(thd, &lst, &num_tables,
MYSQL_OPEN_FORCE_SHARED_HIGH_PRIO_MDL))
{
my_error(ER_TRG_CANT_OPEN_TABLE, MYF(0),
(const char *) trg_name->m_db.str,
(const char *) lst->table_name);
return TRUE;
goto exit;
/* Perform closing actions and return error status. */
}
Table_triggers_list *triggers= lst->table->triggers;
triggers= lst->table->triggers;
if (!triggers)
{
my_error(ER_TRG_DOES_NOT_EXIST, MYF(0));
return TRUE;
goto exit;
}
int trigger_idx= triggers->find_trigger_by_name(&trg_name->m_name);
trigger_idx= triggers->find_trigger_by_name(&trg_name->m_name);
if (trigger_idx < 0)
{
@@ -7826,16 +7830,22 @@ bool show_create_trigger(THD *thd, const sp_name *trg_name)
(const char *) trg_name->m_db.str,
(const char *) lst->table_name);
return TRUE;
goto exit;
}
return show_create_trigger_impl(thd, triggers, trigger_idx);
error= show_create_trigger_impl(thd, triggers, trigger_idx);
/*
NOTE: if show_create_trigger_impl() failed, that means we could not
send data to the client. In this case we simply raise the error
status and client connection will be closed.
*/
exit:
close_thread_tables(thd);
/* Release any metadata locks taken during SHOW CREATE TRIGGER. */
thd->mdl_context.rollback_to_savepoint(mdl_savepoint);
return error;
}
class IS_internal_schema_access : public ACL_internal_schema_access