On 02/10/2015 06:28 AM, Attila Fazekas wrote:
----- Original Message -----
From: "Jay Pipes" <jaypi...@gmail.com>
To: "Attila Fazekas" <afaze...@redhat.com>, "OpenStack Development Mailing List (not 
for usage questions)"
<openstack-dev@lists.openstack.org>
Cc: "Pavel Kholkin" <pkhol...@mirantis.com>
Sent: Monday, February 9, 2015 7:15:10 PM
Subject: Re: [openstack-dev] [all][oslo.db][nova] TL; DR Things everybody 
should know about Galera

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.

Galere does not replicates the row-level locks created by UPDATE/INSERT ...
So what to do with the UPDATE?

No, Galera replicates the write sets (binary log segments) for UPDATE/INSERT/DELETE statements -- the things that actually change/add/remove records in DB tables. No locks are replicated, ever.

Why should I handle the FOR UPDATE differently?

Because SELECT FOR UPDATE doesn't change any rows, and therefore does not trigger any replication event in Galera.

See here:

http://www.percona.com/blog/2014/09/11/openstack-users-shed-light-on-percona-xtradb-cluster-deadlock-issues/

-jay

https://groups.google.com/forum/#!msg/codership-team/Au1jVFKQv8o/QYV_Z_t5YAEJ

Best,
-jay


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