On Thu, Mar 22, 2012 at 9:07 AM, Robert Haas <robertmh...@gmail.com> wrote: > However, looking at this a bit more, I think the > checkpoint-sync-pause-v1 patch contains an obvious bug - the GUC is > supposedly represented in seconds (though not marked with GUC_UNIT_S, > oops) but what the sleep implements is actually *tenths of a second*. > So I think I'd better rerun these tests with checkpoint_sync_pause=30 > so that I get a three-second delay rather than a > three-tenths-of-a-second delay between each fsync.
OK, I did that, rerunning the test with just checkpoint-sync-pause-v1 and master, still with scale factor 1000 and 32 clients. Tests were run on the two branches in alternation, so checkpoint-sync-pause-v1, then master, then checkpoint-sync-pause-v1, then master, etc.; with a new initdb and data load each time. TPS numbers: checkpoint-sync-pause-v1: 2594.448538, 2600.231666, 2580.041376 master: 2466.399991, 2450.752843, 2291.613305 90th percentile latency: checkpoint-sync-pause-v1: 1487, 1488, 1481 master: 1493, 1519, 1507 That's about a 6% increase in throughput and about a 1.3% reduction in 90th-percentile latency. On the other hand, the two timed checkpoints on the master branch, on each test run, are exactly 15 minutes apart, whereas with the patch, they're 15 minutes and 30-40 seconds apart, which may account for some of the difference. I'm going to do a bit more testing to try to isolate that. I'm attaching a possibly-interesting graph comparing the first checkpoint-sync-pause-v1 run against the second master run; I chose that particular combination because those are the runs with the median tps results. It's interesting how eerily similar the two runs are to each other; they have spikes and dips in almost the same places, and what looks like random variation is apparently not so random after all. The graph attached here is based on tps averaged over ten second intervals. Thoughts? Comments? Ideas? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
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