UPDATE performance degradation (6.5.1)

Hi,

after I got DBIlogging work, I run several tests and noticed performance
degradation when doing sequential updating of *one* row.

I have 5 processes updated the same row. I use
LOCK TABLE hits IN SHARE ROW EXCLUSIVE MODE

When I run 200 requests I got about 16 req/sec, which is quite enough
for my purposes. I expected the same speed if I just increase a number of
requests, but it decreases. for 2000 requests I got about 10 req/sec
and for 20,000 - about 2.5 req/sec !
I see no reason for such performance degradation - no way to use
postgres for logging in 24*7*365 Web-site. Probably this is very
specific case when several processes updates only one row,
but again, I see no reason for such big degradation.
Table hits itself contains only 1 row !
I'll try to elimanate httpd, perl in my test bench to test only
postgres, I dont' have right now such a tool, probable someone
already did this ? What tool I can use for testing concurrent update

Regards,
Oleg

This is my home machine, Linux 2.2.10. postgres 6.5.1
Load is about 2-2.5

Typical output of ps:

11:21[om]:/usr/local/apache/logs>psg disc
1036 ? S 24:17 /usr/local/pgsql/bin/postgres localhost httpd discovery LOCK
1040 ? R 24:09 /usr/local/pgsql/bin/postgres localhost httpd discovery idle
1042 ? S 24:02 /usr/local/pgsql/bin/postgres localhost httpd discovery LOCK
1044 ? R 23:51 /usr/local/pgsql/bin/postgres localhost httpd discovery idle
1046 ? S 23:49 /usr/local/pgsql/bin/postgres localhost httpd discovery LOCK
1048 ? S 23:47 /usr/local/pgsql/bin/postgres localhost httpd discovery LOCK

I see only one process with SELECT, this is what I expected when use
IN SHARE ROW EXCLUSIVE MODE. Right ?

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83