On Wed, Dec 24, 2014 at 10:30:19AM +0100, Andres Freund wrote: > On 2014-12-23 22:51:22 -0500, Bruce Momjian wrote: > > Many of these are 64-byte aligned, including Buffer Descriptors. > > In that case you need to change max_connections, some settings will lead > to unaligned BufferDescriptors.
Well, isn't my second patch that misaligns the buffers sufficient for testing? > > I tested pgbench with these commands: > > > > $ pgbench -i -s 95 pgbench > > $ pgbench -S -c 95 -j 95 -t 100000 pgbench > > > > on a 16-core Xeon server and got 84k tps. I then applied another patch, > > attached, which causes all the structures to be non-64-byte aligned, but > > got the same tps number. > > 'Xeon' itself doesn't say much. It's been applied to widly different > CPUs over the years. I guess that was a single socket server? You're > much more likely to see significant problems on a multi node NUMA > servers where the penalties for cache misses/false sharing are a > magnitude or three higher. Sorry, the server has 2 x Intel Xeon E5620 2.4GHz Quad-Core Processors; the full details are here: http://momjian.us/main/blogs/pgblog/2012.html#January_20_2012 > > Can someone test these patches on an AMD CPU and see if you see a > > difference? Thanks. > > I don't think you'll see a bigger difference there. Uh, I thought AMD showed a huge difference for misalignment: http://www.postgresql.org/message-id/20140202151319.gd32...@awork2.anarazel.de and that email is from you. I ended up running pgbench using 16-scale and got 90k tps: pgbench -S -c 16 -j 16 -t 100000 pgbench but again could not see any difference between aligned and misaligned. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers