On 2014-09-12 23:17:12 +0300, Ants Aasma wrote: > On Fri, Sep 12, 2014 at 10:38 PM, Heikki Linnakangas > <hlinnakan...@vmware.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.
I think that might not be a bad plan. But it'll involve *far* more effort and arguing to change to fundamentally different algorithms. So personally I'd just go with slice-by-4. that's relatively uncontroversial I think. Then maybe switch the polynom so we can use the CRC32 instruction. > 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. FWIW, I don't think it's 'bad' that less data provides speedups. I don't really see a need to see that get that out of the benchmarks. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers