[DRBD-user] MySQL-over-DRBD Performance

Art Age Software artagesw at gmail.com
Sat Dec 15 22:52:35 CET 2007

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Dec 15, 2007 1:45 PM, Florian Haas <florian.haas at linbit.com> wrote:
> On Saturday 15 December 2007 20:32:51 Art Age Software wrote:
> > It seems that there is a lot of uncertainty out there regarding how to
> > best configure MySQL on DRBD. Some sort of "best practices" document
> > with configuration settings for DRBD and MySQL would be a huge help in
> > this regard. I realize there are a lot of variables to take into
> > consideration. But having some solid tested examples to start from
> > would be quite helpful. Anyone up to the task?  :)
> That would be me, I suppose. :-)
> About the performance issues you mentioned. The performance tests I've
> conducted were run using mysqlslap, and backed up using some lower-level
> latency tests, but test results were similar initially. Going back to the
> test results you've reported:
> > Old Servers (2 single-core CPUs):
> >       Database on Local Storage
> >               insert test:  212.00 sec.
> >       Database on DRBD Device
> >               insert test:  998.00 sec.
> >       ----------------------------
> >       DRBD Overhead:  786 sec. = 370%
> Eliminate competition for CPU resources between DRBD an MySQL, by pinning
> DRBD's kernel threads to one CPU core and mysqld on the other, like so
> (assuming drbd0 is your device you're running your MySQL databases on):
> for thread in worker asender receiver; do
>   taskset -p 0x01 $(pidof drbd0_$thread)
> done
> taskset -p 0x02 $(pidof mysqld)
> If you're unfamiliar with taskset, be sure to read its man page to understand
> what those CPU affinity masks mean.
> Do that, then re-run your tests (on your old server) and share your results.
> That tweak alone reduced my DRBD overhead for mysqlslap from 224% to 57% on
> the test system I have at my disposal.
> > New Servers (2 quad-core CPUs):
> >       Database on Local Storage
> >               insert test:  164.00 sec.       (22% better than old servers)
> >       Database on DRBD Device
> >               insert test:  1137.00 sec.      (14% *worse* than old servers)
> >       ----------------------------
> >       DRBD Overhead:  973 sec. = 590%
> Yup, now given the CPU resource competition issues described earlier, these
> are probably being exacerbated by the fact that there are now 8 logical
> CPUs (cores) available, versus 2 on your old server. You can do one of two
> things here:
> 1. Pin the DRBD threads to one core, and allocate the others to MySQL.
> 2. Pin the DRBD threads to one core, and allocate only a few of the others to
> MySQL. I've heard some SMP issues are present in InnoDB; more cores doesn't
> necessarily mean better performance.
> There are other settings that can be tweaked (I can come down to about 26%
> overhead on my system, which is about as low as the network will let me), but
> I'd be interested to learn whether you can confirm my results with regard to
> CPU affinity tweaking.
> Cheers,
> Florian

Thank you very much for the suggestions, Florian. I will experiment
with the CPU affinity today and report my findings back to the list.
Unfortunately, I can only do so on the new servers as the old ones are
currently running in production and I can't risk breaking them.  :)


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