On 2015-01-02 12:06:33 -0500, Bruce Momjian wrote: > On Fri, Jan 2, 2015 at 05:55:52PM +0100, Andres Freund wrote: > > On 2015-01-02 11:52:42 -0500, Bruce Momjian wrote: > > > Why are we not seeing the 33% compression and 15% performance > > > improvement he saw? What am I missing here? > > > > To see performance improvements something needs to be the bottleneck. If > > WAL writes/flushes aren't that in the tested scenario, you won't see a > > performance benefit. Amdahl's law and all that. > > > > I don't understand your negativity about the topic. > > I remember the initial post from Masao in August 2013 showing a > performance boost, so I assumed, while we had the concurrent WAL insert > performance improvement in 9.4, this was going to be our 9.5 WAL > improvement.
I don't think it makes sense to compare features/improvements that way. > While the WAL insert performance improvement required no tuning and > was never a negative It's actually a negative in some cases. > , I now see the compression patch as something that has negatives, so > has to be set by the user, and only wins in certain cases. I am > disappointed, and am trying to figure out how this became such a > marginal win for 9.5. :-( I find the notion that a multi digit space reduction is a "marginal win" pretty ridiculous and way too narrow focused. Our WAL volume is a *significant* problem in the field. And it mostly consists out of FPWs spacewise. > My negativity is not that I don't want it, but I want to understand why > it isn't better than I remembered. You are basically telling me it was > always a marginal win. :-( Boohoo! No, I didn't. I told you that *IN ONE BENCHMARK* wal writes apparently are not the bottleneck. 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