kstat.zfs.misc.arcstats.hash_collisions

[Pawel Jakub Dawidek]

On Fri, Apr 16, 2010 at 01:19:38AM +0300, Andriy Gapon wrote:
> kstat.zfs.misc.arcstats.hash_elements: 8465
> kstat.zfs.misc.arcstats.hash_elements_max: 336855
> kstat.zfs.misc.arcstats.hash_collisions: 3463061
> kstat.zfs.misc.arcstats.hash_chains: 549
> kstat.zfs.misc.arcstats.hash_chain_max: 19
> 
> Doesn't hash_collisions value look fishy?
> I haven't looked at the code yet.  Perhaps stats gathering is not correct,
> perhaps something else, but collisions value is really too high for my taste.

The hash_collisions counter is increased every time we try to add buffer
to the list and something is already there. I think more important
counter here is hash_chain_max, which contains maximum number of buffers
on one list ever recorded. And 19 doesn't seem like a big number.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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