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------------------------------------------------------------ revno: 2617.68.10 committer: Dmitry Lenev <dlenev@mysql.com> branch nick: mysql-next-bg46673 timestamp: Tue 2009-09-01 19:57:05 +0400 message: Fix for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK and DML". Deadlocks occured when one concurrently executed transactions with several statements modifying data and FLUSH TABLES WITH READ LOCK statement or SET READ_ONLY=1 statement. These deadlocks were introduced by the patch for WL 4284: "Transactional DDL locking"/Bug 989: "If DROP TABLE while there's an active transaction, wrong binlog order" which has changed FLUSH TABLES WITH READ LOCK/SET READ_ONLY=1 to wait for pending transactions. What happened was that FLUSH TABLES WITH READ LOCK blocked all further statements changing tables by setting global_read_lock global variable and has started waiting for all pending transactions to complete. Then one of those transactions tried to executed DML, detected that global_read_lock non-zero and tried to wait until global read lock will be released (i.e. global_read_lock becomes 0), indeed, this led to a deadlock. Proper solution for this problem should probably involve full integration of global read lock with metadata locking subsystem (which will allow to implement waiting for pending transactions without blocking DML in them). But since it requires significant changes another, short-term solution for the problem is implemented in this patch. Basically, this patch restores behavior of FLUSH TABLES WITH READ LOCK/ SET READ_ONLY=1 before the patch for WL 4284/bug 989. By ensuring that extra references to TABLE_SHARE are not stored for active metadata locks it changes these statements not to wait for pending transactions. As result deadlock is eliminated. Note that this does not change the fact that active FLUSH TABLES WITH READ LOCK lock or SET READ_ONLY=1 prevent modifications to tables as they also block transaction commits. mysql-test/r/flush_block_commit.result: Adjusted test case after change in FLUSH TABLES WITH READ LOCK behavior - it is no longer blocked by a pending transaction. mysql-test/r/mdl_sync.result: Added test for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK and DML". mysql-test/r/read_only_innodb.result: Adjusted test case after change in SET READ_ONLY behavior - it is no longer blocked by a pending transaction. mysql-test/t/flush_block_commit.test: Adjusted test case after change in FLUSH TABLES WITH READ LOCK behavior - it is no longer blocked by a pending transaction. mysql-test/t/mdl_sync.test: Added test for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK and DML". mysql-test/t/read_only_innodb.test: Adjusted test case after change in SET READ_ONLY behavior - it is no longer blocked by a pending transaction. sql/sql_base.cc: Disable caching of pointers to TABLE_SHARE objects in MDL subsystem. This means that transactions holding metadata lock on the table will no longer have extra reference to the TABLE_SHARE (due to this lock) and will no longer block concurrent FLUSH TABLES/FLUSH TABLES WITH READ LOCK. Note that this does not change the fact that FLUSH TABLES WITH READ LOCK prevents concurrent transactions from modifying data as it also blocks all commits.
85 lines
1.5 KiB
Text
85 lines
1.5 KiB
Text
# should work with embedded server after mysqltest is fixed
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-- source include/not_embedded.inc
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-- source include/have_innodb.inc
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#
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# BUG#11733: COMMITs should not happen if read-only is set
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#
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--disable_warnings
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DROP TABLE IF EXISTS table_11733 ;
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--enable_warnings
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# READ_ONLY does nothing to SUPER users
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# so we use a non-SUPER one:
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grant CREATE, SELECT, DROP on *.* to test@localhost;
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connect (con1,localhost,test,,test);
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connection default;
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set global read_only=0;
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# Any transactional engine will do
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create table table_11733 (a int) engine=InnoDb;
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connection con1;
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BEGIN;
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insert into table_11733 values(11733);
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connection default;
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set global read_only=1;
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connection con1;
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select @@global.read_only;
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select * from table_11733 ;
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--error ER_OPTION_PREVENTS_STATEMENT
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COMMIT;
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connection default;
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set global read_only=0;
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drop table table_11733 ;
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drop user test@localhost;
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disconnect con1;
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#
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# Bug #35732: read-only blocks SELECT statements in InnoDB
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#
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# Test 1: read only mode
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GRANT CREATE, SELECT, DROP ON *.* TO test@localhost;
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connect(con1, localhost, test, , test);
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connection default;
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CREATE TABLE t1(a INT) ENGINE=INNODB;
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INSERT INTO t1 VALUES (0), (1);
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SET GLOBAL read_only=1;
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connection con1;
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SELECT * FROM t1;
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BEGIN;
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SELECT * FROM t1;
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COMMIT;
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connection default;
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SET GLOBAL read_only=0;
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#
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# Test 2: global read lock
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#
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FLUSH TABLES WITH READ LOCK;
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connection con1;
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SELECT * FROM t1;
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BEGIN;
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SELECT * FROM t1;
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COMMIT;
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connection default;
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UNLOCK TABLES;
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DROP TABLE t1;
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DROP USER test@localhost;
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disconnect con1;
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--echo echo End of 5.1 tests
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