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Re: How to optimize/defragment RAM usage of mysqld
Posted by: Rick James
Date: February 20, 2016 12:13AM

Main memory (RAM) is managed by the OS in 4KB "pages". Any page can be anywhere in your 48GB. Every page is equally accessible. (NUMA notwithstanding.) Your software is (presumably) "64-bit. Hence, there is no such thing as "fragmentation" in RAM. Period. Full stop.

38G buffer_pool in 48GB of RAM should be fine. (I say 70% because that is safer when I don't know how much RAM a user has. Your 80% should not be a problem on a server dedicated to MySQL.)

Defragmentation on disk _may_ have _some_ benefit for _spinning_ drives. It is absolutely useless for SSDs.

If you would like further analysis of your settings, please provide SHOW VARIABLES; and SHOW GLOBAL STATUS;

If you are having performance problems, set long_query_time=1, turn on the slowlog, wait a day, then run pt-query-digest or mysqldumpslow -s t on the slowlog. The first couple of queries are usually the ones that can be fixed to give you a significant performance boost. Post another question if you need help with a query.

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Re: How to optimize/defragment RAM usage of mysqld
February 20, 2016 12:13AM

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