| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Teodor Sigaev <teodor(at)sigaev(dot)ru>, David Rowley <dgrowleyml(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: hash_create API changes (was Re: speedup tidbitmap patch: hash BlockNumber) |
| Date: | 2014-12-24 16:58:45 |
| Message-ID: | 8466.1419440325@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)2ndquadrant(dot)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
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