From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: valiouk@yahoo.co.uk, pgsql-docs@postgresql.org, dx k9 <bitsandbytes88@hotmail.com>
Subject: Re: [ADMIN] shared_buffers and shmmax
Date: Tue, 16 Dec 2008 22:31:15 -0500
Message-ID: <20538.1229484675@sss.pgh.pa.us> (raw)
In-Reply-To: <200812170133.mBH1Xac23918@momjian.us>
References: <200812170133.mBH1Xac23918@momjian.us>
Bruce Momjian <bruce@momjian.us> 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
regards, tom lane
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Subject: Re: [ADMIN] shared_buffers and shmmax
In-Reply-To: <20538.1229484675@sss.pgh.pa.us>
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