Multiple CPUs and MyISAM

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Dear all,

I'm running MySQL 5.0.82 with a 16GB database, on a dedicated machine with
16 cores (4 x 4) and 64 GB of memory. It has 100 tables, of which 2 have
been recently converted to InnoDB to alleviate table locks which were
causing problems, and the rest are MyISAM.

Observing the system under load again, it seems that at a certain point the
increase in load is no longer linear with the increase in concurrent users.
At that point, the system starts doing more context switching (from ~3000,
to ~160,000). Is that enough to conclude that the problem here is thread
thrashing?

What can I do in MySQL, and more specifically, MyISAM in order to possibly
control this? Do you think the situation can be improved by switching to
InnoDB?

I've been reading that MySQL performance on SMP has been improved (or is in
the process of), however it's unclear to me which improvements made it to
5.0.x, if any, and whether the improvements are for InnoDB only or MyISAM
too.

Any suggestions or pointers are very welcome. Thank you.

Kind Regards,

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Amr Mostafa

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