| From: | Ants Aasma <ants(at)cybertec(dot)at> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Rahila Syed <rahilasyed90(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com>, Rahila Syed <rahilasyed(dot)90(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [REVIEW] Re: Compression of full-page-writes |
| Date: | 2014-09-12 20:17:12 |
| Message-ID: | CA+CSw_vAKMz80WiNUZNt_5XHyqR4YUinfTQO_H+Cnk31W33osQ@mail.gmail.com |
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On Fri, Sep 12, 2014 at 10:38 PM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> I don't mean that we should abandon this patch - compression makes the WAL
> smaller which has all kinds of other benefits, even if it makes the raw TPS
> throughput of the system worse. But I'm just saying that these TPS
> comparisons should be taken with a grain of salt. We probably should
> consider switching to a faster CRC algorithm again, regardless of what we do
> with compression.
CRC is a pretty awfully slow algorithm for checksums. We should
consider switching it out for something more modern. CityHash,
MurmurHash3 and xxhash look like pretty good candidates, being around
an order of magnitude faster than CRC. I'm hoping to investigate
substituting the WAL checksum algorithm 9.5.
Given the room for improvement in this area I think it would make
sense to just short-circuit the CRC calculations for testing this
patch to see if the performance improvement is due to less data being
checksummed.
Regards,
Ants Aasma
--
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de
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