[GRLUG] FYI - old mysql and new gear

[Bob Kline]

You can alter the "affinity," whatever
that exactly means, but the scheduler
apparently does not permit assigning
a CPU to a task, useful as that sometimes
seems like it would be.  In fact, one's control
over how CPU's are assigned seems
rather limited.

"Nice"  - man nice - has long existed,
starting in Unix, to allow one to alter
process priority.  If I remember
correctly - if not, that's what man pages
are for.... - a positive integer, up to 19,
lowers priority, contrary to one's intuition,
and can be done by an ordinary user.
I believe you have to be root to increase
priority, a.k.a. "niceness."

Here again, the scheduler has the last
word, but it's worth a try.

   -- Bob


On Mon, Sep 19, 2011 at 4:45 PM, Michael Mol <mikemol at gmail.com> wrote:

> On Mon, Sep 19, 2011 at 4:36 PM,  <scott.tanner at comcast.net> wrote:
> > Just thought I'd share an interesting discovery with the group.  This may
> be
> > common knowledge to others, but it was a bit of a surprise to me.   We're
> in
> > the process of upgrading the servers which run our primary MySQL DB's
> > (version 5.1):
> >
> >   Old Server                    New Server
> > ---------------------------------------------------------
> >    Sun X4200                 Silicon Mechanics R516
> >     4 x 2.4GHz                 12 x 3.2GHz (+ HT = 24 threads)
> >     16GB Ram                  144GB Ram
> >   12 disks - SCSI             24 disks - SAS & SSD
> >
> >
> > After getting the new servers setup and our databases copied over, I ran
> > sysbench to get some performance benchmarks of the new servers.
> Surprise  -
> > performance was nearly identical or slightly worse.  I disabled HT, still
> no
> > real improvement.   After a bit of searching on the web, I found the
> older
> > versions of MySQL had issues with multi-threading beyond 8 threads.  I
> setup
> > an init script to hot-remove CPU's via sysfs, and voila - performance
> > increased substantially.   There are patches from Yahoo, Google, and
> Percona
> > to correct this issue on the older MySQL versions, and the newer versions
> > are supposedly better at handling 32+ threads.
>
> Very interesting.
>
> A thought...Rather than removing your extra cores, perhaps there's
> some way to set CPU affinity, so MySQL is only allowed to use eight of
> them? That way, the other processes on your system can stay out of the
> way of your database server, and spend cycles on other cores.
>
> If you get affinities working, you might also consider running
> multiple instances of mysqld, putting different databases on different
> sets of cores.
>
>
> --
> :wq
>
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