[MDEV-468] Galera: Server does not honor metadata locking (even inside the same node) Created: 2012-08-20  Updated: 2012-09-20  Resolved: 2012-08-20

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: None
Fix Version/s: 5.5.25-galera

Type: Bug Priority: Major
Reporter: Elena Stepanova Assignee: Seppo Jaakola
Resolution: Not a Bug Votes: 0
Labels: None

Issue Links:
Relates
relates to MDEV-523 Galera: Server crashes with SIGABRT, ... Closed
relates to MDEV-542 Galera: Assertion `! is_set() || can_... Closed

 Description    

--connection con1
 
CREATE TABLE t1 (i INT PRIMARY KEY);
 
BEGIN;
 
INSERT INTO t1 VALUES (1);
 
 
 
--connection con2
 
ALTER TABLE t1 ADD COLUMN b CHAR;
 
 
 
--connection con1
 
COMMIT;

Normally, in the scenario above the 2nd connection would wait for a metadata lock on t1 until con1 finishes the transaction, or lock_wait_timeout occurs, whichever happens first. However, if server is running as a Galera node, ALTER TABLE is executed right away, despite the locks that con1 holds; and the transaction in con1 will be rejected.

Explicit BEGIN/COMMIT here are just to make the test deterministic, in fact it happens just as well on a single-statement transaction with autocommit.

Limitations page (http://www.codership.com/wiki/doku.php?id=limitations) mentions LOCK statements, but does not say that internal locking is also not supported. Besides, this kind of scenario does not involve any other nodes.

bzr version-info

revision-id: seppo.jaakola@codership.com-20120808224721-89h8nxmfk9uvp708
 
date: 2012-08-09 01:47:21 +0300
 
build-date: 2012-08-20 20:31:14 +0400
 
revno: 3343



 Comments   
Comment by Seppo Jaakola [ 2012-08-20 ]

Galera processes all DDL statements under "Total Order Isolation", where the DDL statement is replicated up front and with high priority.
In this test scenario the con1 DML transaction (BEGIN; INSERT...) is still local state and not known by replicator when the ALTER from con2 is replicated. Then ALTER will gain higher priority and will override the DML transaction. This is natural behavior for DDLs in Galera Cluster.

Comment by Seppo Jaakola [ 2012-08-20 ]

This is expected behaviour of DDL processing in Galera Cluster

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