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From:Jon Olav Hauglid Date:October 5 2010 10:25am
Subject:bzr commit into mysql-5.5-runtime branch (jon.hauglid:3153) Bug#57002
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#At file:///export/home/x/mysql-5.5-runtime-bug57002/ based on revid:jon.hauglid@stripped

 3153 Jon Olav Hauglid	2010-10-05
      Bug #57002 Assert in upgrade_shared_lock_to_exclusive()
                 for ALTER TABLE + MERGE tables
      
      The patch for Bug#56292 changed how metadata locks are taken for MERGE
      tables. After the patch, locking the MERGE table will also lock the
      children tables with the same metadata lock type. This means that 
      LOCK TABLES on a MERGE table also will implicitly do LOCK TABLES on
      the children tables.
      
      A consequence of this change, is that it is possible to do LOCK TABLES
      on a child table both explicitly and implicitly with the same statement
      and that these two locks can be of different strength. For example,
      LOCK TABLES child READ, merge WRITE.
      
      In LOCK TABLES mode, we are not allowed to take new locks and each
      statement must therefore try to find an existing TABLE instance with
      a suitable lock. The code that searched for a suitable TABLE instance,
      only considered table level locks. If a child table was locked twice,
      it was therefore possible for this code to find a TABLE instance with
      suitable table level locks but without suitable metadata lock.
      
      This problem caused the assert in upgrade_shared_lock_to_exclusive()
      to be triggered as it tried to upgrade a MDL_SHARED lock to
      EXCLUSIVE. The problem was a regression caused by the patch for
      Bug#56292.
      
      This patch fixes the problem by partially reverting the changes
      done by Bug#56292. Now, the children tables will only use the
      same metadata lock as the MERGE table for MDL_SHARED_NO_WRITE
      when not in locked tables mode. This means that LOCK TABLE
      on a MERGE table will not implicitly lock the children tables.
      This still fixes the original problem in Bug#56292 without
      causing a regression.
      
      Test case added to merge.test.

    modified:
      mysql-test/r/merge.result
      mysql-test/t/merge.test
      storage/myisammrg/ha_myisammrg.cc
=== modified file 'mysql-test/r/merge.result'
--- a/mysql-test/r/merge.result	2010-09-30 10:43:43 +0000
+++ b/mysql-test/r/merge.result	2010-10-05 10:25:30 +0000
@@ -3486,12 +3486,13 @@ ALTER TABLE m1 ADD INDEX (c1);
 UNLOCK TABLES;
 DROP TABLE m1, t1;
 #
-# Locking the merge table will implicitly lock children.
+# Locking the merge table won't implicitly lock children.
 #
 CREATE TABLE t1 (c1 INT);
 CREATE TABLE m1 (c1 INT) ENGINE=MRG_MyISAM UNION=(t1);
 LOCK TABLE m1 WRITE;
 ALTER TABLE t1 ADD INDEX (c1);
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
 LOCK TABLE m1 WRITE, t1 WRITE;
 ALTER TABLE t1 ADD INDEX (c1);
 UNLOCK TABLES;
@@ -3661,4 +3662,16 @@ REPAIR TABLE t2 USE_FRM;
 Table	Op	Msg_type	Msg_text
 test.t2	repair	note	The storage engine for the table doesn't support repair
 DROP TABLE t1, t2;
+#
+# Bug#57002 Assert in upgrade_shared_lock_to_exclusive()
+#           for ALTER TABLE + MERGE tables
+#
+DROP TABLE IF EXISTS t1, m1;
+CREATE TABLE t1(a INT) engine=myisam;
+CREATE TABLE m1(a INT) engine=merge UNION(t1);
+LOCK TABLES t1 READ, m1 WRITE;
+ALTER TABLE t1 engine=myisam;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+UNLOCK TABLES;
+DROP TABLE m1, t1;
 End of 6.0 tests

=== modified file 'mysql-test/t/merge.test'
--- a/mysql-test/t/merge.test	2010-09-30 10:43:43 +0000
+++ b/mysql-test/t/merge.test	2010-10-05 10:25:30 +0000
@@ -2600,11 +2600,12 @@ UNLOCK TABLES;
 DROP TABLE m1, t1;
 
 --echo #
---echo # Locking the merge table will implicitly lock children.
+--echo # Locking the merge table won't implicitly lock children.
 --echo #
 CREATE TABLE t1 (c1 INT);
 CREATE TABLE m1 (c1 INT) ENGINE=MRG_MyISAM UNION=(t1);
 LOCK TABLE m1 WRITE;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
 ALTER TABLE t1 ADD INDEX (c1);
 LOCK TABLE m1 WRITE, t1 WRITE;
 ALTER TABLE t1 ADD INDEX (c1);
@@ -2776,6 +2777,27 @@ REPAIR TABLE t2 USE_FRM;
 DROP TABLE t1, t2;
 
 
+--echo #
+--echo # Bug#57002 Assert in upgrade_shared_lock_to_exclusive()
+--echo #           for ALTER TABLE + MERGE tables
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS t1, m1;
+--enable_warnings
+
+CREATE TABLE t1(a INT) engine=myisam;
+CREATE TABLE m1(a INT) engine=merge UNION(t1);
+LOCK TABLES t1 READ, m1 WRITE;
+
+# This caused an assert
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+ALTER TABLE t1 engine=myisam;
+
+UNLOCK TABLES;
+DROP TABLE m1, t1;
+
+
 --echo End of 6.0 tests
 
 --disable_result_log

=== modified file 'storage/myisammrg/ha_myisammrg.cc'
--- a/storage/myisammrg/ha_myisammrg.cc	2010-09-08 08:25:37 +0000
+++ b/storage/myisammrg/ha_myisammrg.cc	2010-10-05 10:25:30 +0000
@@ -478,8 +478,9 @@ int ha_myisammrg::add_children_list(void
     /* Set the expected table version, to not cause spurious re-prepare. */
     child_l->set_table_ref_id(mrg_child_def->get_child_table_ref_type(),
                               mrg_child_def->get_child_def_version());
-    /* Use the same metadata lock type for children. */
-    child_l->mdl_request.set_type(parent_l->mdl_request.type);
+    if (! thd->locked_tables_mode &&
+        parent_l->mdl_request.type == MDL_SHARED_NO_WRITE)
+      child_l->mdl_request.set_type(MDL_SHARED_NO_WRITE);
     /* Link TABLE_LIST object into the children list. */
     if (this->children_last_l)
       child_l->prev_global= this->children_last_l;


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Thread
bzr commit into mysql-5.5-runtime branch (jon.hauglid:3153) Bug#57002Jon Olav Hauglid5 Oct
  • Re: bzr commit into mysql-5.5-runtime branch (jon.hauglid:3153)Bug#57002Dmitry Lenev6 Oct