[MDEV-633] LP:1024058 - mysqld XA crash in replication slave Created: 2012-07-12  Updated: 2013-01-21  Resolved: 2013-01-21

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: 5.5.28
Fix Version/s: 5.5.29

Type: Bug Priority: Critical
Reporter: Rich Prohaska Assignee: Sergei Golubchik
Resolution: Fixed Votes: 0
Labels: Launchpad, replication

Attachments: XML File LPexportBug1024058.xml    

 Description   

We found a simple XA transaction that crashes MySQL 5.5 replication. This simple transaction merely inserts into InnoDB and TokuDB tables. The bug was caused by a flaw in the logging code exposed by the transaction’s use of two XA storage engines (TokuDB and InnoDB) and was fixed in the TokuDB 6.0.1 release.

Here are some details. Suppose that a database contains the following tables.

create table t1 (a int) engine=InnoDB
 
create table t2 (a int) engine=TokuDB

The following transaction

begin
 
insert into t1 values (1)
 
insert into t2 values (2)
 
commit

causes the replication slave to crash.

The crash occurs when mysqld tries to dereference a NULL pointer.

#4  0x000000000088e203 in MYSQL_BIN_LOG::log_and_order (this=0x14b8640, thd=0x7f7758000af0, xid=161, all=true, need_prepare_ordered=false, need_commit_ordered=true) at /home/mariadb-5.5.25/sql/log.cc:7491
 
7491	  cache_mngr->using_xa= TRUE;
 
(gdb) p cache_mngr
 
$1 = (binlog_cache_mngr *) 0x0

the bug is fixed on lp:~prohaska7/5.5-xa-rpl-crash-fix

also, see mariadb-developers email thread.

 Comments   
Comment by Rasmus Johansson (Inactive) [ 2012-07-12 ]

Launchpad bug id: 1024058

Comment by Sergei Golubchik [ 2012-11-14 ]

Although none of your patch is present in the current MariaDB 5.5, I failed to reproduce the crash with InnoDB and PBXT and the your test case.

If you could provide more info, so that I'd be able to reproduce it, feel free to reopen this bug.

Comment by Sergei Golubchik [ 2012-12-14 ]

got more info from the reporter

Comment by Sergei Golubchik [ 2013-01-17 ]

The problem here is very simple to explain. The server can use either mmap-based transaction coordinator for 2PC or a binary log. 2PC always uses binary log, if binary logging is enabled. But even if it is enabled globally, it is usually disabled in the replication slave thread unless --log-slave-updates is specified.

One would probably get the same crash without replication, if one disables binary log manually with SET SQL_LOG_BIN=0;

Possible fixes:

  • auto-enable binary log for 2PC transactions (bad, binlog will contain unwanted DDL and DML events).
  • abort 2PC transactions if binary log is locally disabled for this thread (worse, too easy to break the replication)
  • write Xid events to binlog even if binary log is locally disabled (best?)

The last approach seems to be preferable. But in the future if we'll start recovering transactions from the binary log (doing only one sync per 2PC transaction), we'll have this problem again, because then we'll need the actual changes to be logged, not just the Xid.

knielsen - opinion?

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