On Fri, Dec 12, 2014 at 05:19:42PM +0100, Andres Freund wrote: > On 2014-12-12 11:15:46 -0500, Robert Haas wrote: > > On Fri, Dec 12, 2014 at 11:12 AM, Andres Freund <and...@anarazel.de> wrote: > > > On 2014-12-12 11:08:52 -0500, Robert Haas wrote: > > >> Unless I'm missing something, this test is showing that FPW > > >> compression saves 298MB of WAL for 17.3 seconds of CPU time, as > > >> against master. And compressing the whole record saves a further 1MB > > >> of WAL for a further 13.39 seconds of CPU time. That makes > > >> compressing the whole record sound like a pretty terrible idea - even > > >> if you get more benefit by reducing the lower boundary, you're still > > >> burning a ton of extra CPU time for almost no gain on the larger > > >> records. Ouch! > > > > > > Well, that test pretty much doesn't have any large records besides FPWs > > > afaics. So it's unsurprising that it's not beneficial. > > > > "Not beneficial" is rather an understatement. It's actively harmful, > > and not by a small margin. > > Sure, but that's just because it's too simplistic. I don't think it > makes sense to make any inference about the worthyness of the general > approach from the, nearly obvious, fact that compressing every tiny > record is a bad idea.
Well, it seems we need to see some actual cases where compression does help before moving forward. I thought Amit had some amazing numbers for WAL compression --- has that changed? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
