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Re: [ADMIN] shared_buffers and shmmax

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, valiouk(at)yahoo(dot)co(dot)uk, pgsql-docs(at)postgresql(dot)org, dx k9 <bitsandbytes88(at)hotmail(dot)com>
Subject: Re: [ADMIN] shared_buffers and shmmax
Date: 2008-12-17 13:41:40
Message-ID: 200812171341.mBHDfeK11281@momjian.us (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-docspgsql-hackers
Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)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

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  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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