Received: from localhost (unknown [200.46.204.183]) by mail.postgresql.org (Postfix) with ESMTP id 6FA3564FEB3 for ; Wed, 17 Dec 2008 09:41:48 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 76280-01 for ; Wed, 17 Dec 2008 09:41:45 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from momjian.us (momjian.us [70.90.9.53]) by mail.postgresql.org (Postfix) with ESMTP id 5457964FE31 for ; Wed, 17 Dec 2008 09:41:45 -0400 (AST) Received: (from bruce@localhost) by momjian.us (8.11.6/8.11.6) id mBHDfeK11281; Wed, 17 Dec 2008 08:41:40 -0500 (EST) From: Bruce Momjian Message-Id: <200812171341.mBHDfeK11281@momjian.us> Subject: Re: [ADMIN] shared_buffers and shmmax In-Reply-To: <20538.1229484675@sss.pgh.pa.us> To: Tom Lane Date: Wed, 17 Dec 2008 08:41:40 -0500 (EST) CC: Alvaro Herrera , valiouk@yahoo.co.uk, pgsql-docs@postgresql.org, dx k9 X-Mailer: ELM [version 2.4ME+ PL124 (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="US-ASCII" X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=none X-Spam-Level: X-Archive-Number: 200812/21 X-Sequence-Number: 5028 Tom Lane wrote: > Bruce Momjian writes: > > Tom Lane wrote: > >> If you're going to give a formula, why not just give a formula, eg > > > You mean like this: > > http://momjian.us/tmp/pgsql/kernel-resources.html > > Yeah, more or less. A couple thoughts now that I see it worked out: > > * Combining the entries for max_connections and autovacuum_max_workers > is probably just making it look more complicated than it needs to. > How about two rows that just happen to have similar formulas, viz > > max_connections (1800 + 270 * max_locks_per_transaction) * max_connections > autovacuum_max_workers (1800 + 270 * max_locks_per_transaction) * autovacuum_max_workers > > * The right-hand column header should be something like "Approximate > shared memory bytes..." to avoid the impression that these formulas > are meant to be exact. > > * If we do it like this then the left-hand column is really redundant, > not to say wrong because the right-hand formulas depend on more than > the single variable mentioned. How about something like > > Table 17-2 PostgreSQL shared memory usage > > Purpose Approximate number of bytes required (as of 8.3) > > Per-connection state (1800 + 270 * max_locks_per_transaction) * max_connections > Autovacuum worker state (1800 + 270 * max_locks_per_transaction) * autovacuum_max_workers > Prepared transaction state ... > Shared disk buffers ... > WAL buffers ... > Fixed space requirements 770kB OK, I updated it again: http://momjian.us/tmp/pgsql/kernel-resources.html I did change your left column wording because it could be interpreted as something that changes during server execution, e.g. connections. -- Bruce Momjian http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +