Re: SHMMAX and shared_bufffers

Scott Marlowe escribió:
> On Tue, Nov 11, 2008 at 10:58 AM, Sam Mason <sam(at)samason(dot)me(dot)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.