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From:Raphael Bauduin Date:August 29 2012 9:16am
Subject:Re: qcache settings and block meaning
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On Tue, Aug 28, 2012 at 6:40 PM, Rick James <rjames@stripped> wrote:
>> | Qcache_hits                       | 56418967     |
>> | Qcache_inserts                    | 48601636     |
> That's a low hit rate.  Perhaps you should simply turn off the Query cache?
>
>> | Qcache_free_memory                | 46945512     |
> That's a big fraction of the total.  Either the QC is unnecessarily big, or it was
> recently purged.

It hasn't been purged resultly AFAIK.

>
>> | Qcache_lowmem_prunes              | 21948806     |
> What is Uptime?  This may be a lot of prunes per second.

Uptime is 65days, resulting in a little less than 4 per second.
>
> Purging stuff out of 128MB _may_ slow your system down more than the benefit you are
> getting.
> I recommend turning off the QC for systems with constant write activity.
> Otherwise, 50M is a reasonable max.

Thanks for your feedback. These question were going to be the topic of
my next mail to the list, but you anticipated correctly :-)

Raph

>
>> -----Original Message-----
>> From: raphinou@stripped [mailto:raphinou@stripped] On Behalf Of
>> Raphael Bauduin
>> Sent: Tuesday, August 28, 2012 7:12 AM
>> To: mysql@stripped
>> Subject: qcache settings and block meaning
>>
>> Hi,
>>
>> I have a mysql server running with the query cache size being 128M
>> (134217728 bytes).
>>
>> Here are the qcache variables values:
>>
>> | Qcache_free_blocks                | 13758        |
>> | Qcache_free_memory                | 46945512     |
>> | Qcache_hits                       | 56418967     |
>> | Qcache_inserts                    | 48601636     |
>> | Qcache_lowmem_prunes              | 21948806     |
>> | Qcache_not_cached                 | 39066097     |
>> | Qcache_queries_in_cache           | 44858        |
>> | Qcache_total_blocks               | 104668
>>
>> And the query_cache_min_res_unit is 4096 .
>>
>> I'm not sure what the meaning of a block is. For the query cache size
>> and the number of total blocks, I have a block size of
>> 134217728/104668 = 1282.3186 , which is a strange number for a block
>> size. Am I wrong somewhere?
>>
>> Thanks
>>
>> Raph
>>
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>



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Thread
qcache settings and block meaningRaphael Bauduin28 Aug
  • Re: qcache settings and block meaningJohan De Meersman28 Aug
  • RE: qcache settings and block meaningRick James28 Aug
    • Re: qcache settings and block meaningRaphael Bauduin29 Aug
      • RE: qcache settings and block meaningRick James29 Aug
        • Re: qcache settings and block meaningRaphael Bauduin30 Aug