Date: Tue, 23 Mar 2004 13:12:00 -0800 From: Dror Matalon <dror@zapatec.com> To: freebsd-performance@freebsd.org Subject: Re: FreeBSD, PostgreSQL, semwait and sbwait! Message-ID: <20040323211200.GZ1757@rlx11.zapatec.com> In-Reply-To: <200403232002.i2NK2Gam077177@mail.gotfrag.com> References: <200403232002.i2NK2Gam077177@mail.gotfrag.com>
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Databases tend to be io bound not cpu bound. Try running something like iostat 5 and see how disk utilization varies between testing and production. If it's taking 3 seconds to run a query that should take 50ms, I would guess that it's fetching pages from disk. Also, I'd suggest asking this question with lots more information about the kind of queries you're running, on the postgresql-performance mailing list. There's a lot more traffic there and knowledgeable people. Dror On Tue, Mar 23, 2004 at 03:02:22PM -0500, Jason Coene wrote: > Hello all, > > We're having a substantial problem with our FreeBSD 5.2 database server > running PostgreSQL - it's getting a lot of traffic (figure about 3,000 > queries per second), but queries are slow, and it's seemingly waiting on > other things than CPU time. > > The database server is a dual P4-2.8 w/ HT enabled (kernel finds 4 > processors), 2GB RAM, 4 disk Serial ATA on 3ware RAID, gigabit Ethernet > connection to web servers. It's running FreeBSD 5.2 and PostgreSQL 7.4.1. > > The server is taking a while to respond to both connections, and then > queries (between 1-3 seconds, on a query that should execute in 0.05 or > less). > > The CPU usage for the server never goes above 30% (70% idle), and the CPU > time that's in use is nearly always split equal between user and system. > The system is using > > Doing a "top", this is what we see: > > last pid: 51833; load averages: 13.72, 11.74, 10.01 up 0+01:55:45 15:00:03 > 116 processes: 1 running, 99 sleeping, 16 lock > CPU states: 14.6% user, 0.0% nice, 23.7% system, 0.2% interrupt, 61.5% idle > Mem: 91M Active, 1043M Inact, 160M Wired, 52K Cache, 112M Buf, 644M Free > Swap: 4096M Total, 4096M Free > > 20354 pgsql 131 0 80728K 5352K select 0 0:24 1.71% 1.71% postgres > 36415 pgsql 4 0 81656K 67468K sbwait 2 0:00 3.23% 0.59% postgres > 36442 pgsql 128 0 82360K 15868K select 2 0:00 1.75% 0.24% postgres > 36447 pgsql -4 0 82544K 10616K semwai 0 0:00 2.05% 0.20% postgres > 36461 pgsql -4 0 81612K 6844K semwai 2 0:00 2.05% 0.20% postgres > 36368 pgsql 4 0 82416K 20780K sbwait 3 0:00 0.50% 0.15% postgres > 36459 pgsql -4 0 81840K 7816K semwai 0 0:00 1.54% 0.15% postgres > 36469 pgsql -4 0 81840K 7964K semwai 2 0:00 1.54% 0.15% postgres > 36466 pgsql 129 0 81840K 7976K *Giant 2 0:00 1.54% 0.15% postgres > 36479 pgsql -4 0 81528K 6648K semwai 0 0:00 3.00% 0.15% postgres > 36457 pgsql -4 0 81840K 8040K semwai 1 0:00 1.03% 0.10% postgres > 36450 pgsql 129 0 82352K 8188K *Giant 2 0:00 1.03% 0.10% postgres > 36472 pgsql -4 0 81824K 7416K semwai 2 0:00 1.03% 0.10% postgres > 36478 pgsql 131 0 81840K 7936K select 0 0:00 2.00% 0.10% postgres > 36454 pgsql 4 0 82416K 16300K sbwait 3 0:00 0.51% 0.05% postgres > 36414 pgsql 4 0 82416K 15872K sbwait 2 0:00 0.27% 0.05% postgres > > Our kernel is GENERIC plus: > > maxusers 512 > options SYSVSHM > options SHMMAXPGS=262144 > options SHMSEG=512 > options SHMMNI=512 > options SYSVSEM > options SEMMNI=512 > options SEMMNS=1024 > options SEMMNU=512 > options SEMMAP=512 > options NMBCLUSTERS=32768 > > Interesting bits from postgresql.conf: > > max_connections = 512 > shared_buffers = 8192 > sort_mem = 16384 > vacuum_mem = 8192 > fsync = false > > It seems that queries are executing fine once they start, but it's taking a > while for them to get going, while the postgres process sits in semwait, > sbwait or select. This problem doesn't happen when there's little load on > the server, it's only when we open it for public consumption that it > exhibits these problems. > > Anyone have this type of problem before? Am I missing something? > > Thanks, Jason > > _______________________________________________ > freebsd-performance@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-performance > To unsubscribe, send any mail to "freebsd-performance-unsubscribe@freebsd.org" -- Dror Matalon Zapatec Inc 1700 MLK Way Berkeley, CA 94709 http://www.fastbuzz.com http://www.zapatec.com
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