On 2014-09-16 15:43:06 +0530, Amit Kapila wrote: > On Sat, Sep 13, 2014 at 1:33 AM, Heikki Linnakangas <hlinnakan...@vmware.com> > wrote: > > On 09/12/2014 10:54 PM, Abhijit Menon-Sen wrote: > >> At 2014-09-12 22:38:01 +0300, hlinnakan...@vmware.com wrote: > >>> We probably should consider switching to a faster CRC algorithm again, > >>> regardless of what we do with compression. > >> > >> As it happens, I'm already working on resurrecting a patch that Andres > >> posted in 2010 to switch to zlib's faster CRC implementation. > > > > As it happens, I also wrote an implementation of Slice-by-4 the other day > :-). > > Haven't gotten around to post it, but here it is. > > Incase we are using the implementation for everything that uses > COMP_CRC32() macro, won't it give problem for older version > databases. I have created a database with Head code and then > tried to start server after applying this patch it gives below error: > FATAL: incorrect checksum in control file
That's indicative of a bug. This really shouldn't cause such problems - at least my version was compatible with the current definition, and IIRC Heikki's should be the same in theory. If I read it right. > In general, the idea sounds quite promising. To see how it performs > on small to medium size data, I have used attached test which is > written be you (with some additional tests) during performance test > of WAL reduction patch in 9.4. Yes, we should really do this. > The patched version gives better results in all cases > (in range of 10~15%), though this is not the perfect test, however > it gives fair idea that the patch is quite promising. I think to test > the benefit from crc calculation for full page, we can have some > checkpoint during each test (may be after insert). Let me know > what other kind of tests do you think are required to see the > gain/loss from this patch. I actually think we don't really need this. It's pretty evident that slice-by-4 is a clear improvement. > I think the main difference in this patch and what Andres has > developed sometime back was code for manually unrolled loop > doing 32bytes at once, so once Andres or Abhijit will post an > updated version, we can do some performance tests to see > if there is any additional gain. If Heikki's version works I see little need to use my/Abhijit's patch. That version has part of it under the zlib license. If Heikki's version is a 'clean room', then I'd say we go with it. It looks really quite similar though... We can make minor changes like additional unrolling without problems lateron. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
