MySQL Bugs: #26540: relay-log.info out of sync after crash

Bug #26540	relay-log.info out of sync after crash
Submitted:	21 Feb 2007 21:02	Modified:	26 Feb 2007 12:14
Reporter:	Kolbe Kegel
Status:	Verified
Category:	Server: Replication	Severity:	S3 (Non-critical)
Version:	5.0	OS:	Any
Assigned to:	Alfranio Correia	Target Version:
Tags:	bfsm_2007_03_01
Triage:	Triaged: D2 (Serious) / R5 (Severe) / E5 (Major)

Description:
If the Slave crashes between the time the server executes and commits a transactional
statement and the time the server would have updated and synced the relay-log.info file,
the Exec_Master_Log_Pos value in relay-log.info could be inconsistent with the
transactions actually applied to any transactional engines.

How to repeat:
Difficult...

Suggested fix:
Either...

1. Use XA for relay-log.info
2. Store relay-log info in a transactional table

The suggested solution for this bug is in WL#3970.

Adding link to public worklog.
http://forge.mysql.com/worklog/task.php?id=3970

Please check BUG#31665.

Details:

- For MySQL 6.0, this is already fixed for most failure scenarious by
  the implementation of a relay log synchronization feature
  (specified in BUG#31665).

- For MySQL 6.0, with the synchronization feature enabled, there are
  today some performance problems.  These problems are reported as
  BUG#40337 and this will be fixed for 6.0.

- The feature introduced in MySQL 6.0 (BUG#31665) has already proven
  useful for some users and it makes replication withstands some hard
  tests.  The complete solution with complete transactional relay log
  synchronization will probably be implemented in 6.1 to cover the few
  remaining situations where the relay log can be incorrect.

Lars,
You are more of an optimist than I am with your use of 'most' and 'few'. Prior to the
sync_binlog changes the sequence is:
1) commit to innodb
2) write updated relay-log.info

with the change the sequence is:
1) commit to innodb
2) write updated relay-log.info
3) sync relay-log.info

Then a crash before step 3) still leaves the storage engine and relay-log.info out of
sync.