Re: [PATCH] two-arg current_setting() with fallback

> On Mar 20, 2015, at 11:10 AM, David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>
> On Fri, Mar 20, 2015 at 9:04 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Mar 20, 2015 at 10:54 AM, David Christensen <david(at)endpoint(dot)com> wrote:
> > In that case, the other thought I had here is that we change the function signature of current_setting() to be a two-arg form where the second argument is a boolean "throw_error", with a default argument of true to preserve existing semantics, and returning NULL if that argument is false. However, I'm not sure if there are some issues with changing the signature of an existing function (e.g., with pg_upgrade, etc.).
> >
> > My *impression* is that since pg_upgrade rebuilds the system tables for a new install it shouldn't be an issue, but not sure if having the same pg_proc OID with different values or an alternate pg_proc OID would cause issues down the line; anyone know if this is a dead-end?
>
> I think if the second argument is defaulted it would be OK. However
> it might make sense to instead add a new two-argument function and
> leave the existing one-argument function alone, because setting
> default arguments for functions defined in pg_proc.h is kind of a
> chore.
>
> ​Isn't there some other update along this whole error-vs-null choice going around where a separate name was chosen for the new null-returning function instead of adding a boolean switch argument?

Well, speaking of the two-arg form vs alternate name, here's a version of the patch which includes the new behavior. (I couldn't think of a good name to expose for an alternate function, but I'm open to suggestions.)

Regards,

David
--
David Christensen
End Point Corporation
david(at)endpoint(dot)com
785-727-1171