changing max_connections in postgresql on FreeBSD 5.4

[Claus Guttesen]

Hi.

I recently lowered max_connections from 1024 to 384 in
/usr/local/pgsql/data/postgresql.conf. The server is a quad opteron @
2 GHz and 4 GB of RAM.

This decreased the SIZE and RES values in top and it seems that the
current max_connections is more than adequate. To see how many
concurrent connections the db-server had I did a 'netstat -na|grep -i
establi|wc -l' which showed some 230 established connections during
peak.

In order to use max_connections set to 1024 I had to raise the
following values in the kernel:

options         SHMMAXPGS=327680
options         SEMMNI=200
options         SEMMNS=1200
options         SEMUME=200
options         SEMMNU=600

The values were taken from the postgresql-ports-installation-notes and
were simply increased to fit the max_connections-parameter in
postgresql.conf.

Will more RAM become available to postgresql if I change the
kernel-values mentioned above to half the size?

The server does occasionally become loaded with load-averages around 6
or 7 but usually stays below 4. Disk-io is not a problem, usually
remains below 1 MB/s, cpu-idle is approx. 5-10 % during peak and
around 80 % idle otherwise.

regards
Claus