Re: SHMMAX and shared_bufffers

Scott Marlowe escribió:
> On Tue, Nov 11, 2008 at 10:58 AM, Sam Mason <sam@samason.me.uk> wrote:

> > what is this "extra slop" needed for?

> free space map and temp buffers.  Not sure what else.

Lock space, pg_clog, pg_subtrans and pg_multixact buffers, FSM, and some
other things.  External modules can request additional shared memory
too.  We're not very strict about the accounting.

(temp buffers do not use shared memory -- what would be the point?)

> Note that there could always be some other application using some
> small amount of shared memory.  use ipcs to see it.  Run it as root to
> see other user's / process's shared mem usage.

shmmax is per-process.  It's shmall that's system-wide, but that's
measured in pages and is rarely a problem.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.