Date: Mon, 3 Apr 2000 02:55:56 +0200 From: "Marinos J . Yannikos" <mjy@pobox.com> To: questions@freebsd.org Subject: tuning the vm system / disk cache Message-ID: <20000403025556.S31173@TK147108.telekabel.at>
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I'm trying to reduce the number of disk accesses during database queries -
the database is very small, there's plenty of RAM available, and the queries
are simple SELECT queries (i.e. read-only). I am using the following kernel
options:
maxusers 256
options SOFTUPDATES
options SHMMAXPGS=65536
options SHMSEG=32
(the last 2 because I'm using postgres)
The whole database takes up approx. 12MB disk space, the system looks like
this:
Mem: 26M Active, 13M Inact, 25M Wired, 36K Cache, 12M Buf, 438M Free
Swap: 490M Total, 490M Free
The filesystem used is mounted with -o async (not that it should matter -
except perhaps for the logfiles, which only grow by a few 100 bytes per
second anyway).
Still, the disk seems to be accessed frequently during the queries:
k7# iostat 5
tty ad0 acd0 fd0 cpu
tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id
1 88 0.00 0 0.00 0.00 0 0.00 0.00 0 0.00 51 0 4 0 45
0 15 96.26 9 0.86 0.00 0 0.00 0.00 0 0.00 86 0 7 0 6
0 15 95.46 14 1.32 0.00 0 0.00 0.00 0 0.00 78 0 6 0 16
0 15 85.39 12 1.02 0.00 0 0.00 0.00 0 0.00 85 0 6 0 9
0 15 100.55 13 1.31 0.00 0 0.00 0.00 0 0.00 79 0 5 0 16
0 16 97.71 12 1.18 0.00 0 0.00 0.00 0 0.00 83 0 5 0 12
0 15 106.29 10 0.99 0.00 0 0.00 0.00 0 0.00 80 0 8 0 12
0 16 100.16 18 1.72 0.00 0 0.00 0.00 0 0.00 77 0 5 0 18
Is there any way to force a more aggressive caching by the vm system? I have
looked at the sysctl variables, but my attempts at tuning them weren't very
successful.
Any input would be much appreciated.
-mjy
--
***==> Marinos J. Yannikos <mjy@pobox.com>
***==> http://pobox.com/~mjy
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