Re: ALTER SYSTEM SET command to change postgresql.conf parameters (RE: Proposal for Allow postgresql.conf values to be changed via SQL [review])

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Robert Haas escribi�:
>> On Mon, Jul 22, 2013 at 7:56 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> I'd be inclined to think that ALTER SYSTEM SET should not be allowed to
>>> modify any PGC_POSTMASTER parameters.

>> That significantly decreases the usefulness of ALTER SYSTEM without
>> actually preventing the underlying problem.  If having multiple
>> conflicting values for parameters in the config files doesn't work
>> cleanly, then we should fix that, not cripple this feature.

> I think the only solution that makes sense here is to comment out the
> entry in postgresql.conf.

Actually, this is much ado about nothing.  If you actually put two
conflicting values for shared_buffers into postgresql.conf, you'll
find out that:

1. on initial start, the server just silently adopts the later one.

2. if you SIGHUP, you get:

LOG:  autovacuum launcher started
LOG:  received SIGHUP, reloading configuration files
LOG:  parameter "shared_buffers" cannot be changed without restarting the server
LOG:  configuration file "/home/postgres/version93/data/postgresql.conf" contains errors; unaffected changes were
applied

We could possibly improve the code to not produce that log bleat, but
it's hardly a show-stopper as is.
        regards, tom lane