Re: Add default_val to pg_settings

Simon Riggs <simon@2ndQuadrant.com> writes:
> We have an RESET command which "returns parameter to its default
> setting". But what this means is "return it to the value set in current
> the postgresql.conf, if overriden therein from its default value". So it
> would be useful to have a column that meant "if I run the RESET command
> it would return me to this value".

> The boot value is only interesting when the "source" column of
> pg_settings is "default". In all other cases it is a misleading value,
> AFAICS. It would be accurate in sessions that have not run SET, or have
> just issued RESET ALL, but we have no way of knowing whether that is the
> case or not.

Right, this is why I was complaining that the view should expose the
reset_val.  Greg's opinion that only boot_val is needed seems to be
focused entirely on DBAs or tools for manipulating postgresql.conf ---
the only reason you'd want to know boot_val is to know "what will happen
if I remove this setting from postgresql.conf?".  For ordinary users
boot_val is useless information, but reset_val could be interesting.

> I would suggest we either alter pg_settings so that we display value
> *only* when source=default (set NULL otherwise) or we do some extra work
> to derive what the setting would be if we ran RESET. The latter would be
> preferred approach.

Trying to make one column serve both masters sounds hopelessly confusing
to me; it would essentially make it useless for *both* sets of users,
because neither would know whether the value they're seeing is the one
they need.
        regards, tom lane