On Tue, Apr 12, 2016 at 12:38 PM, Andres Freund <and...@anarazel.de> wrote: > On 2016-04-12 16:49:25 +0000, Kevin Grittner wrote: >> On a big NUMA machine with 1000 connections in saturation load >> there was a performance regression due to spinlock contention, for >> acquiring values which were never used. Just fill with dummy >> values if we're not going to use them. > > FWIW, I could see massive regressions with just 64 connections.
With what settings? With or without the patch to avoid the locks when off? > I'm a bit scared of having an innoccuous sounding option regress things > by a factor of 10. I think, in addition to this fix, we need to actually > solve the scalability issue here to a good degree. One way to do so is > to apply the parts of 0001 in > http://archives.postgresql.org/message-id/20160330230914.GH13305%40awork2.anarazel.de > defining PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY and rely on that. Another > to apply the whole patch and simply put the lsn in an 8 byte atomic. I think that we are well due for atomic access to aligned 8-byte values. That would eliminate one potential hot spot in the "snapshot too old" code, for sure. -- Kevin Grittner EDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers