Merge "wsrep_slave_threads: default to 48 on bionic"
abc9707...
by
OpenDev Sysadmins <email address hidden>
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:
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.
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.
Ensure that EOL releases are removed from metadata
and tests, and that the current dev release is enabled
in metadata. Dev release tests are enabled separately
because of chickens and eggs.
