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Posted by Erwin Moller on 12/01/06 14:27
O.L. wrote:
> Hello,
>
> On my LAMP webserver, I noticed that sometimes the MySQL daemon uses
> 99.99% of the CPU, and does not answer SQL queries, while several
> minutes.
> Does someone know what could be the causes ?
>
> I searched on MySQL.com forums, and I found answers about query cache,
> but this is not enabled on my server.
> I looked the process list (SHOW FULL PROCESSLIST) :
> - almost all the queries where "Locked"
> - almost all queries where SELECT
> - there was no "difficult" query (big UPDATE or big DELETE or REPAIR or
> OPTIMIZE ...)
> My database is mainly used with the 'members' table which contains
> 100000+ records, and a lot of INDEXes. All the queries shown in the
> process list were about this table.
>
> Any idea ? Any solution to prevent this periodical server lag ?
>
> Thanks in advance for your help :)
> Olivier (and excuse my bad english !)
>
Hi Oliver,
You say you have a lot of indexes.
This means that the simple insert or update you mentioned must also update
all these indexes.
Could that explain the high processorload?
Remember that indexes can be usefull, but only if you do a lot more selects
with the indexed columns in the where-clause than you do inserts/updates.
Indexes slow down inserts/updates, but will greatly increase selects, so
use them wisely.
Regards,
Erwin Moller
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