FreeBSD 10 and PostgreSQL 9.3 scalability issues

[Matthew Seaman]

On 03/18/14 03:12, Petr Janda wrote:
> ust want to share these pgbench results done by DragonFlyBSD, and would
> like some input on why these numbers look so bad and what can be done to
> improve (ie. kernel tunables etc) the performance.
> 
> http://lists.dragonflybsd.org/pipermail/users/attachments/20140310/4250b961/attachment-0001.pdf

Using ZFS as the backing for a RDBMS without:

    * Separate (fast) L2ARC devices
    * Tuning the ZFS block size to match the postgres IO block size
    * Setting primarycache to metadata
    * Tuning the ARC max so ZFS doesn't eat all the RAM
    * probably other things I can remember off-hand.

That's what is wrong.  ZFS is known to work particularly badly at the
sort of small random IOs that RDBMSes generate (mostly because of the
copy-on-write thing) without special tuning and extra hardware for
caches.  ie.  You can't construct a fair test of database performance
against other OSes/filesystems if you restrict yourself to using exactly
the same hardware.

Basically, install the FreeBSD box on UFS2 and try again.

	Cheers,

	Matthew


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