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Re: why my Qcache_not_cached is very large?
Posted by: James Day
Date: December 17, 2004 06:42AM

The query cache will only store a query until any one of the tables it uses is changed in any way (adding, changing or deleting a row, for example). If most of your tables are updated frequently you may be caching all possible queries. If this is a performance problem you may find it helpful to take snapshot copies of some key tables regularly and query those instead - if the updates are far less often than updates to your main tables it can save a significant amount of work.

Alternatively, you may not have a sufficiently large query cache, you may have the maximum size of a query to be cached set too low (or too high for the cache size). or the query cache free space may be fragmented. The server system variables part of the manual has several variables for configuring the query cache behavior and the MySQL query cache section of the manual includes a section on cache status and maintenance which may help you to better tune the settings.

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Re: why my Qcache_not_cached is very large?
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