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Re: engine=memory versus query_cache
Posted by: Ingo Strüwing
Date: April 03, 2006 04:49AM

Bodo Fritsche wrote:
...
> The documentation and my runtime information says
> that query_cache_size is defaulted by "0" meaning
> that although query_cache_type ="ON" there is no
> query_caching until query_cache_size and
> query_cache_limit is set.

Yes. It seems like I misinterpreted the docs.

...
> Am I right?: This means that the above mentioned
> memory-table will put a relatively high activity
> (in terms of deleting the table from the
> query_cache) on the query_cache because its fields
> will be updated so often.

Yes. I think so. But if a query is deleted, (almost) nothing needs to be done for the next update. Unless you did a select in between.

> I would have expected that mySQL recognizes that
> if a table is memory, it excludes it from
> query_caching.

Memory tables are not so different from other tables with well filled caches. The purpose of the query cache is not just to save I/O, but also to save computing efforts (e.g for complicated joins). If you have simple statements only, the query cache might not help you much anyway.

Regards

Ingo Strüwing, Senior Software Developer - Storage Engines
MySQL AB, www.mysql.com

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