maria-developers team mailing list archive

[Sergei Golubchik <sergii@xxxxxxxxx>]

Hi, Paul!

On Dec 02, Paul McCullagh wrote:
>>
>> Now, if a binlog doesn't indicate a crash (last binlog file was
>> closed properly, showing a normal shutdown procedure) or, for
>> example, there're no binlog files at all, the server cannot perform
>> the recovery - it doesn't know what transactions should be committed
>> and what transactions should be rolled back. A transaction may be
>> prepared in one engine and already committed (or rolled back) in
>> another. In this case the server requests the user to make the
>> decision, the user has to request an explicit commit or rollback with
>> --tc-heuristic-recover command-line switch.
>
> So if I understand this correctly, tc-heuristic-recover handles a
> situation that should actually never occur.

Yes, that's mainly to account for a user mistake - deleting binlog after
a crash or copying the live datadir from master to a slave without
binlog. Or something similar.

>> But if there's only one XA-capable storage engine, it's always safe to
>> rollback all prepared transactions, there can be no other engine that
>> has them committed. That's what the ifdef-ed code does - if InnoDB is
>> the only XA-capable storage engine on recovery without binlog it forces
>> a rollback of all not committed transactions, preserving the pre-XA
>> InnoDB behavior.
>
> So, in fact, we could change this code:
>
> to:
>
> if (total_ha_2pc == (ulong) opt_bin_log+1) {
>   tc_heuristic_recover= TC_HEURISTIC_RECOVER_ROLLBACK; // forcing ROLLBACK
>   info.dry_run=FALSE;
> }

I intentionally did it with ifdef - the idea was that if there could
*possibly* be another XA-engine, we need to go the safe way. Otherwise
one could, for example, restart the server with disabled pbxt and
unknowingly enable auto-rollback mode, causing inconsistent data.

Regards / Mit vielen Grüßen,
Sergei

-- 
   __  ___     ___ ____  __
  /  |/  /_ __/ __/ __ \/ /   Sergei Golubchik <serg@xxxxxxx>
 / /|_/ / // /\ \/ /_/ / /__  Principal Software Engineer/Server Architect
/_/  /_/\_, /___/\___\_\___/  Sun Microsystems GmbH, HRB München 161028
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