On Sun, Jan 16, 2011 at 10:13 PM, Greg Smith <g...@2ndquadrant.com> wrote: > 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.
I wish I understood better what makes Linux systems "freeze up" under heavy I/O load. Linux - like other UNIX-like systems - generally has reasonably effective mechanisms for preventing a single task from monopolizing the (or a) CPU in the presence of other processes that also wish to be time-sliced, but the same thing doesn't appear to be true of I/O. > 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. Thanks for doing this work. I look forward to the results. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
