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schema

MySQL PERFORMANCE_SCHEMA Hints

Undefined

Accounts not properly closing connections [ 1 ]

SELECT ess.user, ess.host
     , (a.total_connections - a.current_connections) - ess.count_star as not_closed
     , ((a.total_connections - a.current_connections) - ess.count_star) * 100 /
       (a.total_connections - a.current_connections) as pct_not_closed

How MySQL behaves with many schemata, tables and partitions

Introduction

Recently a customer claimed that his queries were slow some times and sometimes they were fast.

First idea: Flipping query execution plan caused by InnoDB could be skipped because it affected mainly MyISAM tables.

Second idea: Caching effects by either the file system cache caching MyISAM data or the MyISAM key buffer caching MyISAM indexes were examined: File system cache was huge and MyISAM key buffer was only used up to 25%.

I was a bit puzzled...

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