Re: Clarify "allow_system_table_mods"

On Mon, Apr 25, 2016 at 8:05 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:

> * Melvin Davidson (melvin6925(at)gmail(dot)com) wrote:
> > Then could you please clarify exactly what structural mods are permitted
> by
> > *"*
> > *Allows modification of the structure of system tables" ?*
>
> I would say, in short, those modifications which are implemented by PG
> developers who know what's safe to do with the catalog tables.
>
> Beyond that, I'm afriad you'd need to read the source code. I don't
> know offhand the complete set of "what's safe to do", though it's
> probably a pretty short list and certainly doesn't include adding
> columns.
>
> Ultimately, that switch isn't for end users to use to modify the
> catalogs. If you'd like to modify the structure of pg_class, you would
> start by looking at src/include/catalog/pg_class.h, though there's quite
> a few other bits that would need to change too.
>
> Thanks!
>
> Stephen
>

>allow_system_table_mods only exists so that initdb can do some setup steps
that would otherwise be inconvenient to manage.

So in essence "*Allows modification of the structure of system tables" does
NOT allow _structural_ changes (probably only dml changes)
and the documentation should be changed to clarify.

--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.