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Re: Memory taken by FSM_relations

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Memory taken by FSM_relations
Date: 2003-02-24 20:17:40
Message-ID: 5221.1046117860@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> I'm not clear on where the memory needed by max_fsm_pages comes from.
> Is it taken out of the shared_buffers, or in addition to them?

In addition to.  Basically max_fsm_pages and max_fsm_relations are used
to ratchet up the postmaster's initial shared memory request to the kernel.

> Further, Joe Conway gave me a guesstimate of 6k per max_fsm_pages
> which seems rather high ...

Quite ;-).  The correct figure is six bytes per fsm_page slot, and
I think about forty bytes per fsm_relation slot (recent versions of
postgresql.conf mention the multipliers, although for some reason
the Admin Guide does not).

			regards, tom lane

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