On 12/24/14, 10:58 AM, Tom Lane wrote:
Andres Freund <and...@2ndquadrant.com> writes:
On 2014-12-24 00:27:39 -0600, Jim Nasby wrote:
pgbench -S -T10 -c 4 -j 4
tps = 9556.356145 (excluding connections establishing)
tps = 9897.324917 (excluding connections establishing)
tps = 9287.286907 (excluding connections establishing)
tps = 10210.130833 (excluding connections establishing)

tps = 32462.754437 (excluding connections establishing)
tps = 33232.144511 (excluding connections establishing)
tps = 33082.436760 (excluding connections establishing)
tps = 33597.904532 (excluding connections establishing)

FWIW, I don't believe these results for one second. It's quite plausible
that there's a noticeable performance benefit, but a factor of three is
completely unrealistic... Could you please recheck?

A possible theory is that the hash change moved some locks into
different partitions causing a large reduction in contention,
but even then 3X seems unlikely.  And of course if that was
the mechanism, the result is still pure luck; other examples
might get worse by the same amount.

I must have screwed something up, because if anything I see a small loss for 
XXH now (but my laptop isn't consistent enough to be sure).

This surprises me given that SMHasher shows XXH to be 50% faster than Spooky 
for 20 byte keys.
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com

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