Hello.
I think you have a big fragmentation of your query cache. Fragmentation
can force the query cache to prune (delete) queries from the cache due
to lack of memory. See:
http://dev.mysql.com/doc/mysql/en/query-cache-configuration.html
Remigiusz Soko$owski <rems@stripped> wrote:
> let's say that we have the following settings:
> Variable_name: query_cache_limit Value: 64kB
> Variable_name: query_cache_size Value: 4MB
>
> and status:
>
> | Qcache_queries_in_cache | 1679 |
> | Qcache_inserts | 2242534 |
> | Qcache_hits | 1058592 |
> | Qcache_lowmem_prunes | 135641 |
> | Qcache_not_cached | 2558808 |
> | Qcache_free_memory | 1717208 |
> | Qcache_free_blocks | 485 |
> | Qcache_total_blocks | 3885 |
>
> I wonder why Qcache_lowmem_prunes grows, even though Qcache_free_memory
> is almost 2MB.
> I thought that queries are thrown from cache only in situation, when:
> 1. there were some changes in data of that query
> 2. there is no memory for new query
>
> and Qcache_free_memory should be close to 0 to achieve the state when
> queries are thrown away.
> Anybody has an explaination for such behaviour?
>
> Thanks in advance
> Remigiusz
>
>
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