Comment 1 for bug 1654086

Theory: I think it's very specifically a 5.5 to 5.6 thing, not necessarily the init sys or server release. performance_schema flipped default values, and now it grabs the mem in advance [1]

So with 5.5, there was no down side to setting max connections way higher than it needed to be or should be. But with 5.6, you pay for that with memory allocation (or potentially OOM, which causes a weird wild goose chase of errors).

I'd lean toward keeing keeping the charm's low default max conn so that it is usuably for non-OpenStack contexts out of the box. Exposing a config flag to bit flip the performance_schema config might be worth exploring. That, or 5.6 users will have to get nitty gritty about tuning their db settings to the resources available.

[1] http://dev.mysql.com/doc/relnotes/mysql/5.6/en/news-5-6-6.html