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I've tried using Percona Cluster as a drop-in replacement for MySQL.

However when templates are saved, each cluster node is updated with a different value for the primary key column template_id in the exp_templates table. The primary key column group_id in the exp_template_groups table is also different on each node when group updates are made or a group is created.

This (obviously) causes database inconsistencies, and templates to disappear depending on which MySQL cluster node they're served by.

Does anyone have any experience or advice on whether or not EE2 with Percona Cluster is possible?

  • I don't have any experience with it (hopefully someone who does will chime in here), but this answer suggests that it is possible: expressionengine.stackexchange.com/a/881/22 – Alex Kendrick Dec 2 '13 at 16:41
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    @AlexKendrick Thanks for the link. I'm actually currently using Percona Server at moment with EE, and it works great. However it's Percona Cluster that I've run into problems with. EE's behaviour with Percona Cluster is a little strange, as I've run many other apps (e.g. Wordpress) in Percona cluster without issue. – Elijah Paul Dec 3 '13 at 2:12
  • Ah, of course. I totally overlooked that. I hope you'll get an answer! – Alex Kendrick Dec 3 '13 at 2:18
  • @AlexKendrick No problem, easily done. I've updated the question to better explain what is going on. Hope I get an answer too. in the mean time I'll keep investigating. – Elijah Paul Dec 3 '13 at 2:20
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Ok.

I changed the storage engine of EE database from MyISAM to InnoDB. And now the database is replicating the primary key columns of the exp_templates and exp_template_groups tables correctly.

It may have something to do with Percona Clusters' limitations:

The main Percona site (Percona XtraDB Cluster Limitations) states:

Currently replication works only with InnoDB storage engine. Any writes to tables of other types, including system (mysql.*) tables, are not replicated.

However numerous blogs on the Percona Blog state that MyISAM replication can be enabled via the my.cnf. But is currently experimental only...

MySQL Performance Blog....

Does replication of MyISAM form any bottlenecks in XtraDB Cluster? If so, how bad?

MyISAM replication in PXC/Galera is labeled as experimental, but I think that’s a misnomer. It should be labeled “broken by design“. MyISAM replication really will never work properly with Galera due to its non-transactional nature.....

For now I'm not sure there's a solid answer on whether MyISAM replication works properly.

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