Update git submodules
* Update charm-percona-cluster from branch 'master' - Merge "wsrep_slave_threads: default to 48 on bionic" - OpenDev Migration Patch This commit was bulk generated and pushed by the OpenDev sysadmins as a part of the Git hosting and code review systems migration detailed in these mailing list posts: http://lists.openstack.org/pipermail/openstack-discuss/2019-March/003603.html http://lists.openstack.org/pipermail/openstack-discuss/2019-April/004920.html Attempts have been made to correct repository namespaces and hostnames based on simple pattern matching, but it's possible some were updated incorrectly or missed entirely. Please reach out to us via the contact information listed at https://opendev.org/ with any questions you may have. - wsrep_slave_threads: default to 48 on bionic This improves performance significantly for environments constrained by calls to sync() such as HDDs or lower-end SSDs (or just very busy environments running many queries) By default the the queries from other nodes are only processed with 1 thread, which means they will always run slower than on the master and any long running query will hold up all other queries behind it. Additionally, when multiple queries commit at once the server can combine them together into a single on-disk sync ('group commit') which is not possible otherwise. This optimisation appears to only occur on Bionic (Percona 5.7) and not Xenial (Percona 5.6). On Bionic, default to 48 threads which experimentally is a good number for OpenStack environments without being too crazy high. Galera ensures that queries that are dependent on each other are still executed sequentially and generally it is not expected to cause replication inconsistencies. However Percona Cluster 5.6 on Xenial appears to have a bug handling foreign key constraints that causes them to be violated (LP #1823850). The result is that the slave node crashes out and has to do a full SST to recover. The same issue is not present on the master. Thus we leave the default wsrep_slave_threads=1 on Xenial to avoid this issue for now particularly since Xenial does not appear to be able to use Group Commit to optimise the number of sync requests generated by the queries - so this option does not really improve performance there anyway. Partial-Bug: #1822903 Change-Id: Ic9cdd6562f30a3e52aa3d26fea53ba7c2bbdc771
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