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

On Mon, Jul 22, 2013 at 7:56 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> Christophe just discovered something with include files which is going
>> to cause issues with ALTER SYSTEM SET.
>
>> So, take as a hypothetical that you use the default postgresql.conf
>> file, which sets shared_buffers = 32MB.
>
>> Instead of editing this file, you do ALTER SYSTEM SET shared_buffers =
>> '1GB', which updates config/postgresql.auto.conf.
>
>> Then you restart PostgreSQL.
>
>> Everything is hunky-dory, until a later occasion where you *reload*
>> postgresql.
>
> Everything was already *not* hunky-dory as soon as you did that, since
> a SIGHUP would have had the same problem.
>
> 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.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company