Andres Freund <andres@2ndquadrant.com> writes:
> On 2014-12-24 00:27:39 -0600, Jim Nasby wrote:
>> pgbench -S -T10 -c 4 -j 4
>> master:
>> tps = 9556.356145 (excluding connections establishing)
>> tps = 9897.324917 (excluding connections establishing)
>> tps = 9287.286907 (excluding connections establishing)
>> tps = 10210.130833 (excluding connections establishing)
>>
>> XXH32:
>> 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.
regards, tom lane