Re: memory strangeness (fwd)

On Sun, 7 Jul 2002 13:06:00 +0900 (JST)
Curt Sampson <cjs@cynic.net> wrote:

> > On this particular system, though, it's doing
> > nothing except PG. 384 MB of RAM, I can give PG 160 of it, which
> > leaves me with some 170 MB of idle RAM.
>
> No, that's not idle RAM; that's buffer cache. (FreeBSD, like most
> modern Unix operating systems, will use any spare physical memory
> to cache blocks read from the disk.) If you allocate 160/170, you
> now have pretty much maximized your chances that postgres and the
> operating system will be buffering the same data, and made your
> memory as minimally effective as possible.

Is there not a method of reading a disk block and instructing the OS not
to buffer it, or am I hallucinating? (My main RDBMS experience experience
is on Solaris, and I could swear that major RDBMSs on that OS will ask the
OS not to buffer disk I/O on behalf of the database)

--
Tim Ellis
DBA, Gamet