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Re: engine=memory versus query_cache
Posted by: Bodo Fritsche
Date: March 31, 2006 02:27AM

Ingo Strüwing wrote:
> Hi,
>
> I might be misunderstanding your question(s).
> Please ask again in this case.
>
> I agree that a table that does not need to be
> stored on disk is a candidate for a memory table.
> Regardless of the type of statements executed on
> it. But please keep in mind that the size of a
> memory table is much more limited than a MyISAM
> table.

This table is very small (1.600 bytes), but updated nearly every few seconds.

>
> I also agree that a table with much more selects
> than changes is a candidate for the query cache.
> But the query cache is active by default. You just
> may want to enlarge it if the hit rate seems
> insufficient for you.

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.

>
> There is just one query cache. But you can turn it
> on and off for every connection individually if
> you like.
>
> All SELECTs for all table types are cached unless
> individualy disabled per connection or even per
> SELECT SQL_NO_CACHE.

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.

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

>
> If you change to a memory table, its SELECTs will
> also be cached. But if these are relatively seldom
> for your table, it should be no problem.
>
> You may already have read this, but just in case:
> http://dev.mysql.com/doc/refman/5.0/en/query-cache
> .html
>
> Regards
>


Thanks Ingo!

Bodo



Edited 6 time(s). Last edit at 03/31/2006 02:32AM by Bodo Fritsche.

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