Re: Spread checkpoint sync

I have finished a first run of benchmarking the current 9.1 code at
various sizes. See http://www.2ndquadrant.us/pgbench-results/index.htm
for many details. The interesting stuff is in Test Set 3, near the
bottom. That's the first one that includes buffer_backend_fsync data.
This iall on ext3 so far, but is using a newer 2.6.32 kernel, the one
from Ubuntu 10.04.

The results are classic Linux in 2010: latency pauses from checkpoint
sync will easily leave the system at a dead halt for a minute, with the
worst one observed this time dropping still for 108 seconds. That one
is weird, but these two are completely averge cases:

http://www.2ndquadrant.us/pgbench-results/210/index.html
http://www.2ndquadrant.us/pgbench-results/215/index.html

I think a helpful next step here would be to put Robert's fsync
compaction patch into here and see if that helps. There are enough
backend syncs showing up in the difficult workloads (scale>=1000,
clients >=32) that its impact should be obvious.

--
Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
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