bzr commit into mysql-5.4 branch (jon.hauglid:2803) Bug#46272

[Jon Olav Hauglid]

#At file:///export/home/z/mysql-next-bugfixing-bug46272/ based on revid:dlenev@stripped

 2803 Jon Olav Hauglid	2009-08-28
      Bug #46272 MySQL 5.4.4, new MDL: unnecessary deadlock
      
      The problem was that ALTER TABLE calls wait_while_table_is_used() 
      which set TABLE_SHARE's version = 0. This happened before 
      ALTER TABLE starts waiting for the shared lock to disappear inside
      upgrade_shared_lock_to_exclusive(). The following UPDATE noticed 
      that share->version now was different from refresh_version and 
      called Open_table_context::request_backoff_action() which 
      triggered the DEADLOCK error.
      
      This patch removes the setting of TABLE_SHARE's version to 0 
      inside wait_while_table_is_used(), since this anyway will 
      be done by close_all_tables_for_name() which is called right
      after the return from wait_while_table_is_used().
      
      Test case added to mdl_sync.test.

    modified:
      mysql-test/r/mdl_sync.result
      mysql-test/t/mdl_sync.test
      sql/sql_base.cc
=== modified file 'mysql-test/r/mdl_sync.result'
--- a/mysql-test/r/mdl_sync.result	2009-08-27 06:22:17 +0000
+++ b/mysql-test/r/mdl_sync.result	2009-08-28 08:55:46 +0000
@@ -233,3 +233,24 @@ drop table t2;
 # Switching to connection 'default'.
 # Clean-up.
 drop table t1;
+#
+# Bug#46272 MySQL 5.4.4, new MDL: unnecessary deadlock
+#
+drop table if exists t1;
+CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT, c3 INT);
+INSERT INTO t1 VALUES (1,1,0),(2,2,0),(3,3,0),(4,4,0),(5,5,0);
+# Connection 1
+SET autocommit=0;
+BEGIN;
+UPDATE t1 SET c3=c3+1 WHERE c2=3;
+# Connection 2
+SET DEBUG_SYNC= 'mdl_upgrade_shared_lock_to_exclusive_wait SIGNAL lock_wait';
+ALTER TABLE t1 ADD COLUMN e INT;
+# Connection 1
+SET DEBUG_SYNC= 'now WAIT_FOR lock_wait';
+UPDATE t1 SET c3=c3+1 WHERE c2=4;
+ROLLBACK;
+Warnings:
+Warning	1196	Some non-transactional changed tables couldn't be rolled back
+DROP TABLE t1;
+SET DEBUG_SYNC= 'RESET';

=== modified file 'mysql-test/t/mdl_sync.test'
--- a/mysql-test/t/mdl_sync.test	2009-08-27 06:22:17 +0000
+++ b/mysql-test/t/mdl_sync.test	2009-08-28 08:55:46 +0000
@@ -438,6 +438,42 @@ disconnect con46044;
 disconnect con46044_2;
 drop table t1;
 
+--echo #
+--echo # Bug#46272 MySQL 5.4.4, new MDL: unnecessary deadlock
+--echo #
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+
+CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT, c3 INT);
+INSERT INTO t1 VALUES (1,1,0),(2,2,0),(3,3,0),(4,4,0),(5,5,0);
+connect (con1,localhost,root,,test,,);
+
+--echo # Connection 1
+connection default;
+SET autocommit=0;
+BEGIN;
+UPDATE t1 SET c3=c3+1 WHERE c2=3;
+
+--echo # Connection 2
+connection con1;
+SET DEBUG_SYNC= 'mdl_upgrade_shared_lock_to_exclusive_wait SIGNAL lock_wait';
+--send ALTER TABLE t1 ADD COLUMN e INT
+
+--echo # Connection 1
+connection default;
+SET DEBUG_SYNC= 'now WAIT_FOR lock_wait';
+UPDATE t1 SET c3=c3+1 WHERE c2=4;
+ROLLBACK;
+
+connection con1;
+reap;
+
+connection default;
+disconnect con1;
+DROP TABLE t1;
+SET DEBUG_SYNC= 'RESET';
 
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.

=== modified file 'sql/sql_base.cc'
--- a/sql/sql_base.cc	2009-08-27 06:22:17 +0000
+++ b/sql/sql_base.cc	2009-08-28 08:55:46 +0000
@@ -2094,11 +2094,6 @@ bool wait_while_table_is_used(THD *thd, 
                        table->s->table_name.str, table->s,
                        table->db_stat, table->s->version));
 
-  /* Ensure no one can reopen table before it's removed */
-  pthread_mutex_lock(&LOCK_open);
-  table->s->version= 0;
-  pthread_mutex_unlock(&LOCK_open);
-
   old_lock_type= table->reginfo.lock_type;
   mysql_lock_abort(thd, table, TRUE);	/* end threads waiting on lock */
 


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