Cherry-picking a patch from Bug 12828477 from mysql-5.5
to mysql-5.5.16-release. Original revision: # revision-id: dmitry.lenev@oracle.com-20110811155849-feyt3h7tj48padiu # parent: tatjana.nuernberg@oracle.com-20110811120945-c6x9a5d2du8s9oj2 # committer: Dmitry Lenev <Dmitry.Lenev@oracle.com> # branch nick: mysql-5.5-12828477 # timestamp: Thu 2011-08-11 19:58:49 +0400 # message: # Fix for bug #12828477 - "MDL SUBSYSTEM CREATES BIG OVERHEAD # FOR CERTAIN QUERIES TO INFORMATION_SCHEMA". # # The problem was that metadata locking subsystem introduced # too much overhead for queries to I_S which were processed by # opening only .FRM or .TRG files and had to scanned a lot of # tables (e.g. SELECT COUNT(*) FROM I_S.TRIGGERS was affected). # The same effect was not observed for similar queries which # performed full-blown table open in order to fill I_S table. # # The problem stemmed from the fact that in case when I_S # implementation opened only .FRM or .TRG file for each table # processed it didn't release metadata lock it has acquired on # the table after finishing its processing. As result, list # of acquired metadata locks were growing until the end of # statement. Since acquisition of each new lock required # search in the list of already acquired locks performance # degraded. # # The same effect is not observed when I_S implementation # performs full-blown table open for each table being # processed, as in the latter cases metadata lock on the # table is released right after table processing. # # This fix addressed the problem by ensuring that I_S # implementation releases metadata lock after processing # the table in both cases of full-blown table open and in # case when only .FRM or .TRG file is read.
This commit is contained in:
Alexander Nozdrin
parent
6e5bbf5138
commit
457cbab0d6
@ -1849,5 +1849,119 @@ unlock tables;
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drop table t1;
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drop view v1;
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#
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# Test for bug #12828477 - "MDL SUBSYSTEM CREATES BIG OVERHEAD FOR
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# CERTAIN QUERIES TO INFORMATION_SCHEMA".
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#
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# Check that metadata locks which are acquired during the process
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# of opening tables/.FRMs/.TRG files while filling I_S table are
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# not kept to the end of statement. Keeping the locks has caused
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# performance problems in cases when big number of tables (.FRMs
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# or .TRG files) were scanned as cost of new lock acquisition has
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# increased linearly.
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drop database if exists mysqltest;
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create database mysqltest;
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use mysqltest;
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create table t0 (i int);
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create table t1 (j int);
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create table t2 (k int);
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#
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# Test that we don't keep locks in case when we to fill
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# I_S table we perform full-blown table open.
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#
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# Acquire lock on 't2' so upcoming RENAME is
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# blocked.
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lock tables t2 read;
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#
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# Switching to connection 'con12828477_1'.
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#
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# The below RENAME should wait on 't2' while
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# keeping X lock on 't1'.
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rename table t1 to t3, t2 to t1, t3 to t2;
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#
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# Switching to connection 'con12828477_2'.
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#
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# Wait while the above RENAME is blocked.
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# Issue query to I_S which will open 't0' and get
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# blocked on 't1' because of RENAME.
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select table_name, auto_increment from information_schema.tables where table_schema='mysqltest';
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#
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# Switching to connection 'con12828477_3'.
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#
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# Wait while the above SELECT is blocked.
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#
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# Check that it holds no lock on 't0' so it can be renamed.
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rename table t0 to t4;
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#
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# Switching to connection 'default'.
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#
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#
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# Unblock the first RENAME.
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unlock tables;
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#
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# Switching to connection 'con12828477_1'.
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#
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# Reap the first RENAME
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#
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# Switching to connection 'con12828477_2'.
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#
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# Reap SELECT to I_S.
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table_name auto_increment
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t0 NULL
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t1 NULL
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t2 NULL
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#
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# Switching to connection 'default'.
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#
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#
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# Now test that we don't keep locks in case when we to fill
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# I_S table we read .FRM or .TRG file only (this was the case
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# for which problem existed).
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#
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rename table t4 to t0;
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# Acquire lock on 't2' so upcoming RENAME is
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# blocked.
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lock tables t2 read;
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#
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# Switching to connection 'con12828477_1'.
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#
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# The below RENAME should wait on 't2' while
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# keeping X lock on 't1'.
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rename table t1 to t3, t2 to t1, t3 to t2;
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#
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# Switching to connection 'con12828477_2'.
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#
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# Wait while the above RENAME is blocked.
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# Issue query to I_S which will open 't0' and get
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# blocked on 't1' because of RENAME.
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select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest';
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#
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# Switching to connection 'con12828477_3'.
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#
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# Wait while the above SELECT is blocked.
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#
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# Check that it holds no lock on 't0' so it can be renamed.
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rename table t0 to t4;
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#
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# Switching to connection 'default'.
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#
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#
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# Unblock the first RENAME.
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unlock tables;
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#
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# Switching to connection 'con12828477_1'.
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#
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# Reap the first RENAME
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#
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# Switching to connection 'con12828477_2'.
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#
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# Reap SELECT to I_S.
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event_object_table trigger_name
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#
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# Switching to connection 'default'.
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#
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#
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# Clean-up.
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drop database mysqltest;
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#
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# End of 5.5 tests
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#
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@ -1543,8 +1543,6 @@ DROP TABLE t1, information_schema.tables;
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LOCK TABLES t1 READ, information_schema.tables READ;
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DROP TABLE t1;
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# Wait till all disconnects are completed
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--source include/wait_until_count_sessions.inc
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#
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# Bug #43834 Assertion in Natural_join_column::db_name() on an I_S query
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@ -1608,6 +1606,186 @@ drop table t1;
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drop view v1;
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--echo #
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--echo # Test for bug #12828477 - "MDL SUBSYSTEM CREATES BIG OVERHEAD FOR
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--echo # CERTAIN QUERIES TO INFORMATION_SCHEMA".
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--echo #
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--echo # Check that metadata locks which are acquired during the process
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--echo # of opening tables/.FRMs/.TRG files while filling I_S table are
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--echo # not kept to the end of statement. Keeping the locks has caused
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--echo # performance problems in cases when big number of tables (.FRMs
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--echo # or .TRG files) were scanned as cost of new lock acquisition has
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--echo # increased linearly.
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--disable_warnings
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drop database if exists mysqltest;
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--enable_warnings
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create database mysqltest;
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use mysqltest;
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create table t0 (i int);
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create table t1 (j int);
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create table t2 (k int);
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--echo #
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--echo # Test that we don't keep locks in case when we to fill
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--echo # I_S table we perform full-blown table open.
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--echo #
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--echo # Acquire lock on 't2' so upcoming RENAME is
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--echo # blocked.
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lock tables t2 read;
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--echo #
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--echo # Switching to connection 'con12828477_1'.
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--echo #
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connect (con12828477_1, localhost, root,,mysqltest);
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--echo # The below RENAME should wait on 't2' while
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--echo # keeping X lock on 't1'.
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--send rename table t1 to t3, t2 to t1, t3 to t2
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--echo #
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--echo # Switching to connection 'con12828477_2'.
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--echo #
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connect (con12828477_2, localhost, root,,mysqltest);
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--echo # Wait while the above RENAME is blocked.
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let $wait_condition=
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select count(*) = 1 from information_schema.processlist
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where state = "Waiting for table metadata lock" and
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info = "rename table t1 to t3, t2 to t1, t3 to t2";
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--source include/wait_condition.inc
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--echo # Issue query to I_S which will open 't0' and get
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--echo # blocked on 't1' because of RENAME.
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--send select table_name, auto_increment from information_schema.tables where table_schema='mysqltest'
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--echo #
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--echo # Switching to connection 'con12828477_3'.
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--echo #
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connect (con12828477_3, localhost, root,,mysqltest);
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--echo # Wait while the above SELECT is blocked.
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let $wait_condition=
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select count(*) = 1 from information_schema.processlist
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where state = "Waiting for table metadata lock" and
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info = "select table_name, auto_increment from information_schema.tables where table_schema='mysqltest'";
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--source include/wait_condition.inc
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--echo #
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--echo # Check that it holds no lock on 't0' so it can be renamed.
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rename table t0 to t4;
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--echo #
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--echo # Switching to connection 'default'.
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--echo #
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connection default;
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--echo #
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--echo # Unblock the first RENAME.
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unlock tables;
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--echo #
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--echo # Switching to connection 'con12828477_1'.
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--echo #
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connection con12828477_1;
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--echo # Reap the first RENAME
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--reap
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--echo #
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--echo # Switching to connection 'con12828477_2'.
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--echo #
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connection con12828477_2;
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--echo # Reap SELECT to I_S.
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--reap
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--echo #
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--echo # Switching to connection 'default'.
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--echo #
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connection default;
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--echo #
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--echo # Now test that we don't keep locks in case when we to fill
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--echo # I_S table we read .FRM or .TRG file only (this was the case
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--echo # for which problem existed).
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--echo #
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rename table t4 to t0;
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--echo # Acquire lock on 't2' so upcoming RENAME is
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--echo # blocked.
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lock tables t2 read;
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--echo #
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--echo # Switching to connection 'con12828477_1'.
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--echo #
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connection con12828477_1;
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--echo # The below RENAME should wait on 't2' while
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--echo # keeping X lock on 't1'.
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--send rename table t1 to t3, t2 to t1, t3 to t2
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--echo #
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--echo # Switching to connection 'con12828477_2'.
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--echo #
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connection con12828477_2;
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--echo # Wait while the above RENAME is blocked.
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let $wait_condition=
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select count(*) = 1 from information_schema.processlist
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where state = "Waiting for table metadata lock" and
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info = "rename table t1 to t3, t2 to t1, t3 to t2";
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--source include/wait_condition.inc
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--echo # Issue query to I_S which will open 't0' and get
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--echo # blocked on 't1' because of RENAME.
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--send select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest'
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--echo #
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--echo # Switching to connection 'con12828477_3'.
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--echo #
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connection con12828477_3;
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--echo # Wait while the above SELECT is blocked.
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let $wait_condition=
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select count(*) = 1 from information_schema.processlist
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where state = "Waiting for table metadata lock" and
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info = "select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest'";
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--source include/wait_condition.inc
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--echo #
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--echo # Check that it holds no lock on 't0' so it can be renamed.
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rename table t0 to t4;
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--echo #
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--echo # Switching to connection 'default'.
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--echo #
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connection default;
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--echo #
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--echo # Unblock the first RENAME.
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unlock tables;
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--echo #
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--echo # Switching to connection 'con12828477_1'.
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--echo #
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connection con12828477_1;
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--echo # Reap the first RENAME
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--reap
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--echo #
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--echo # Switching to connection 'con12828477_2'.
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--echo #
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connection con12828477_2;
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--echo # Reap SELECT to I_S.
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--reap
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--echo #
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--echo # Switching to connection 'default'.
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--echo #
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connection default;
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disconnect con12828477_1;
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disconnect con12828477_2;
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disconnect con12828477_3;
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--echo #
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--echo # Clean-up.
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drop database mysqltest;
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--echo #
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--echo # End of 5.5 tests
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--echo #
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# Wait till all disconnects are completed
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--source include/wait_until_count_sessions.inc
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@ -3157,6 +3157,10 @@ end:
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*/
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thd->temporary_tables= NULL;
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close_thread_tables(thd);
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/*
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Release metadata lock we might have acquired.
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See comment in fill_schema_table_from_frm() for details.
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*/
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thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp);
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thd->lex= old_lex;
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@ -3339,6 +3343,9 @@ try_acquire_high_prio_shared_mdl_lock(THD *thd, TABLE_LIST *table,
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@param[in] db_name database name
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@param[in] table_name table name
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@param[in] schema_table_idx I_S table index
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@param[in] open_tables_state_backup Open_tables_state object which is used
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to save/restore original state of metadata
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locks.
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@param[in] can_deadlock Indicates that deadlocks are possible
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due to metadata locks, so to avoid
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them we should not wait in case if
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@ -3356,6 +3363,7 @@ static int fill_schema_table_from_frm(THD *thd, TABLE_LIST *tables,
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LEX_STRING *db_name,
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LEX_STRING *table_name,
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enum enum_schema_tables schema_table_idx,
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Open_tables_backup *open_tables_state_backup,
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bool can_deadlock)
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{
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TABLE *table= tables->table;
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@ -3501,13 +3509,27 @@ end_share:
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end_unlock:
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mysql_mutex_unlock(&LOCK_open);
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/*
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Don't release the MDL lock, it can be part of a transaction.
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If it is not, it will be released by the call to
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MDL_context::rollback_to_savepoint() in the caller.
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*/
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end:
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/*
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Release metadata lock we might have acquired.
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Without this step metadata locks acquired for each table processed
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will be accumulated. In situation when a lot of tables are processed
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by I_S query this will result in transaction with too many metadata
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locks. As result performance of acquisition of new lock will suffer.
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Of course, the fact that we don't hold metadata lock on tables which
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were processed till the end of I_S query makes execution less isolated
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from concurrent DDL. Consequently one might get 'dirty' results from
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such a query. But we have never promised serializability of I_S queries
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anyway.
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We don't have any tables open since we took backup, so rolling back to
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savepoint is safe.
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*/
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DBUG_ASSERT(thd->open_tables == NULL);
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thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp);
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thd->clear_error();
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return res;
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}
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@ -3758,6 +3780,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
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int res= fill_schema_table_from_frm(thd, tables, schema_table,
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db_name, table_name,
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schema_table_idx,
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&open_tables_state_backup,
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can_deadlock);
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thd->pop_internal_handler();
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