Re: Unsafe GUCs and ALTER SYSTEM WAS: Re: ALTER SYSTEM SET

On Wednesday, August 07, 2013 8:01 AM Bruce Momjian wrote:
> On Tue, Aug  6, 2013 at 09:24:47PM -0400, Greg Smith wrote:
> > # ALTER SYSTEM SET shared_buffers = ‘8GB’ FORCE;
> > NOTICE:  Changing shared_buffers only takes effect after a server
> restart.
> > ALTER SYSTEM
> >
> > Will bad examples pop up in the Internet that just use FORCE all the
> > time?  Sure they will, and people will cut and paste them without
> > paying attention.  I don't see why that possibility has to block
> > this feature from being adopted though.  That line of thinking leads
> > toward removing trust authentication, because that's similarly
> > abused with cut and paste tutorials.
>
> We already have six levels of GUC settings:
>
>     postgresql.conf
>     user
>     database
>     session
>     function
>     subtransaction
>
> If we add ALTER SYSTEM SET and config.d, we would then have eight.
> ALTER SYSTEM SET seems to add an entirely new set of behaviors and
> complexity.  Is that really what we want?
>
> If we do this, perhaps we should unconditionally just print the file
> name they have to delete to undo the operation in case the server
> doesn't start;  I am unclear we can clearly identify all the GUC
> settings that could cause a server not to start.

> Also, I think we need
> a SHOW SYSTEM command so users can see their settings via SQL.

Although users can see the settings in pg_settings as it has sourcefile, but such a command can
be useful.

> FYI, ALTER SYSTEM SET is hitting the same problems we would have if
> pg_hba.conf were set in SQL and in flat files.

With Regards,
Amit Kapila.