On 2014-12-24 10:00:05 -0500, Bruce Momjian wrote: > 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 hadn't looked at it. Note that you're quite likely to overlap the allocated region into the next one with the trivial method you're using. I just verified that I can still reproduce the problem: # aligned case (max_connections=401) afreund@axle:~$ pgbench -P 1 -h /tmp/ -p5440 postgres -n -M prepared -c 96 -j 96 -T 100 -S progress: 1.0 s, 405170.2 tps, lat 0.195 ms stddev 0.928 progress: 2.0 s, 467011.1 tps, lat 0.204 ms stddev 0.140 progress: 3.0 s, 462832.1 tps, lat 0.205 ms stddev 0.154 progress: 4.0 s, 471035.5 tps, lat 0.202 ms stddev 0.154 progress: 5.0 s, 500329.0 tps, lat 0.190 ms stddev 0.132 BufferDescriptors is at 0x7f63610a6960 (which is 32byte aligned) # unaligned case (max_connections=400) afreund@axle:~$ pgbench -P 1 -h /tmp/ -p5440 postgres -n -M prepared -c 96 -j 96 -T 100 -S progress: 1.0 s, 202271.1 tps, lat 0.448 ms stddev 1.232 progress: 2.0 s, 223823.4 tps, lat 0.427 ms stddev 3.007 progress: 3.0 s, 227584.5 tps, lat 0.414 ms stddev 4.760 progress: 4.0 s, 221095.6 tps, lat 0.410 ms stddev 4.390 progress: 5.0 s, 217430.6 tps, lat 0.454 ms stddev 7.913 progress: 6.0 s, 210275.9 tps, lat 0.411 ms stddev 0.606 BufferDescriptors is at 0x7f1718aeb980 (which is 64byte aligned) This is on a quad E5-4620 with 256GB RAM on a scale 100 pgbench instance. > > > 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 Ugh, yes. Forgot that... There was another patch that wasn't showing big differences on AMD, and I mixed it up. > 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. At the very least you should use -M prepared, otherwise you'll be bottlenecked by the parser. 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
