On 6/1/05, Mark Kirkwood <[EMAIL PROTECTED]> wrote:
> Cosimo Streppone wrote:
> > ######### Config ############
> >> /etc/sysctl.conf:
> >> kernel.shmall = 786432000
> >> kernel.shmmax = 786432000
> >
> > I think you have a problem here.
> > kernel.shmmax should *not* be set to an amount of RAM, but
> > to maximum number of shared memory pages, which on a typical linux system
> > is 4kb. Google around:
> >
> This is somewhat confusing :
> kernel.shmmax is in bytes (max single segment size)
> kernel.shmall is in (4k) pages (max system wide allocated segment pages)

Can someone resummarize the situation with these linux parameters for
the dummies? I thought I had my calculations all sorted out but now
I've confused myself again.

The documentation at
puts the same figure into both values but the posts here seem to
suggest that is wrong?
Or is it different on a 2.4 kernel and the documentation needs updating?

In my specific case I have about 800meg of memory on a linux 2.4 kernel box.

Based on the powerpostgresql.com Performance Checklist [1]  and
Annotated Postgresql.conf [2] I understand that:
-I should have less than 1/3 of my total memory as shared_buffers
-For my server 15000 is a fairly reasonable starting point for
shared_buffers which is ~120MB
-I have 100 max_connections.

So I was going to set SHMMAX to 134217728 (ie 128 Meg)

What should SHMALL be?

The current system values are
[EMAIL PROTECTED]:~/data$ cat /proc/sys/kernel/shmmax
[EMAIL PROTECTED]:~/data$ cat /proc/sys/kernel/shmall

ie SHMALL seems to be 1/16 of SHMMAX


[1] http://www.powerpostgresql.com/PerfList/
[2] http://www.powerpostgresql.com/Downloads/annotated_conf_80.html

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