Re: [ADMIN] shared_buffers and shmmax

Tom Lane wrote:
> 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

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.

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  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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