Comment 2 for bug 1654086

The issue with percona cluster is the 5.6 version of mysql defaulting to performance_schema=on [1] at server startup. This allocates all the memory that would be required to handle max-connections plus several other memory settings. See the mysql memory calculator [2] to see how this plays out.

With 5.5 this was not the an issue. We occasionally saw connection exhaustion in HA clouds with max-connections near 2000. The common practice became to set max-connections unrealistically high near 10k or 20k. In the move to 5.6 on Xenial this became a problem.

Discussed this with the team and the plan is to make performance_schema [1] configurable and default to off at startup in the percona cluster charm. This will get us 5.5 like behavior and avoid over committing memory based on max-connections.

Note this is somewhat of a duplicate of [3]

[1] http://dev.mysql.com/doc/relnotes/mysql/5.6/en/news-5-6-6.html#mysqld-5-6-6-performance-schema
[2] http://www.mysqlcalculator.com/
[3] https://bugs.launchpad.net/charms/+source/percona-cluster/+bug/1600001