On 02/11/2015 07:58 AM, Matthew Booth wrote:
On 10/02/15 18:29, Jay Pipes wrote:
On 02/10/2015 09:47 AM, Matthew Booth wrote:
On 09/02/15 18:15, Jay Pipes wrote:
On 02/09/2015 01:02 PM, Attila Fazekas wrote:
I do not see why not to use `FOR UPDATE` even with multi-writer or
Is the retry/swap way really solves anything here.
<snip>
Am I missed something ?
Yes. Galera does not replicate the (internal to InnnoDB) row-level locks
that are needed to support SELECT FOR UPDATE statements across multiple
cluster nodes.
https://groups.google.com/forum/#!msg/codership-team/Au1jVFKQv8o/QYV_Z_t5YAEJ
Is that the right link, Jay? I'm taking your word on the write-intent
locks not being replicated, but that link seems to say the opposite.
This link is better:
http://www.percona.com/blog/2014/09/11/openstack-users-shed-light-on-percona-xtradb-cluster-deadlock-issues/
Specifically the line:
"The local record lock held by the started transation on pxc1 didn’t
play any part in replication or certification (replication happens at
commit time, there was no commit there yet)."
Thanks, Jay, that's a great article.
Based on that, I think I may have misunderstood what you were saying
before. I currently understand that the behaviour of select ... for
update is correct on Galera, it's just not very efficient. Correct in
this case meaning it aborts the transaction due to a correctly detected
lock conflict.
FWIW, that was pretty much my original understanding, but without the
detail.
To expand: Galera doesn't replicate write intent locks, but it turns out
it doesn't have to for correctness. The reason is that the conflict
between a local write intent lock and a remote write, which is
replicated, will always be detected during or before local certification.
Exactly correct.
Best,
-jay
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