Re: 5.1 to 5.5 upgrade causes significant write slowdown (MyISAM + indexes)

[Scott Nemes]

Increasing the memory settings should not cause any issues as long as total usage stays below the max, so I would just make sure to monitor that during the inserts to make sure you are not maxing out as the usage will increase over time. I have seen some issues when you get to a very large buffer pool (like 64GB+ at least) where splitting it up into multiple pools helps out, but that's about it.

Your slow InnoDB speed is likely just a config issue. Since you appear to mainly focus on MyISAM, you likely are not configured optimally for InnoDB. If you want to test that, I would start fresh with a new my.cnf and tailor it to your memory needs as a stand-alone test, making sure to give all your resources to InnoDB and not split it with MyISAM. Percona has a nice tool for generating a my.cnf using input you give it, which serves as a great starting point: https://tools.percona.com/wizard

I'll keep thinking about your MyISAM issue and will update the thread if I come up with anything else, but I'm out of ideas at this moment.

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Scott Nemes
MySQL DBA

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