Re: Wierd context-switching issue on Xeon
От | ohp@pyrenet.fr |
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Тема | Re: Wierd context-switching issue on Xeon |
Дата | |
Msg-id | Pine.UW2.4.53.0404211315000.9232@server.pyrenet.fr обсуждение исходный текст |
Ответ на | Re: Wierd context-switching issue on Xeon (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Wierd context-switching issue on Xeon
(Dirk Lutzebäck <lutzeb@aeccom.com>)
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Список | pgsql-performance |
How long is this test supposed to run? I've launched just 1 for testing, the plan seems horrible; the test is cpu bound and hasn't finished yet after 17:02 min of CPU time, dual XEON 2.6G Unixware 713 The machine is a Fujitsu-Siemens TX 200 server On Mon, 19 Apr 2004, Tom Lane wrote: > Date: Mon, 19 Apr 2004 20:01:56 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: josh@agliodbs.com > Cc: Joe Conway <mail@joeconway.com>, scott.marlowe <scott.marlowe@ihs.com>, > Bruce Momjian <pgman@candle.pha.pa.us>, lutzeb@aeccom.com, > pgsql-performance@postgresql.org, Neil Conway <neilc@samurai.com> > Subject: Re: [PERFORM] Wierd context-switching issue on Xeon > > Here is a test case. To set up, run the "test_setup.sql" script once; > then launch two copies of the "test_run.sql" script. (For those of > you with more than two CPUs, see whether you need one per CPU to make > trouble, or whether two test_runs are enough.) Check that you get a > nestloops-with-index-scans plan shown by the EXPLAIN in test_run. > > In isolation, test_run.sql should do essentially no syscalls at all once > it's past the initial ramp-up. On a machine that's functioning per > expectations, multiple copies of test_run show a relatively low rate of > semop() calls --- a few per second, at most --- and maybe a delaying > select() here and there. > > What I actually see on Josh's client's machine is a context swap storm: > "vmstat 1" shows CS rates around 170K/sec. strace'ing the backends > shows a corresponding rate of semop() syscalls, with a few delaying > select()s sprinkled in. top(1) shows system CPU percent of 25-30 > and idle CPU percent of 16-20. > > I haven't bothered to check how long the test_run query takes, but if it > ends while you're still examining the behavior, just start it again. > > Note the test case assumes you've got shared_buffers set to at least > 1000; with smaller values, you may get some I/O syscalls, which will > probably skew the results. > > regards, tom lane > > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
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