Re: memory strangeness (fwd)

Gregor Mosheh <stigmata(at)blackangel(dot)net> writes:
> Hiya. I've installed Postgres 7.2 on a dedicated FreeBSD system with 384
> MB RAM. Because the system will be doing nothing except PG, I'd like to
> dump as much memory as possible into PG's shared memory.
> I rebuilt the kernel with very large limits: 330 MB on the MAXDSIZ and
> DFLDSIZ, and 330 MB for SHMMAXPAGES. This gives me:

Very likely the kernel has its own ideas on how much memory it needs
to reserve for other purposes, and is unwilling to give you a shmem
segment that represents the bulk of physical RAM.

While I don't know FreeBSD well enough to speculate on exactly why it's
limiting you, I do think that you are going in the wrong direction
for Postgres anyhow. Pretty much everyone who has looked at the issue
has concluded that it's a mistake to try to set shared memory that high.
If you're trying to set it to more than a quarter of physical RAM you're
off track IMHO. In practice, given that this isn't an especially huge
system, I'd think a shared_buffers setting in the low thousands would be
appropriate.

Also, reducing max_connections as low as 5 seems the wrong direction
too ...

regards, tom lane