Re: [ADMIN] shared_buffers and shmmax

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