Re: Truncation of mapped catalogs (whether local or shared) leads to server crash

Hi,

On 2024-06-18 19:58:26 +0530, Ashutosh Sharma wrote:
> On Tue, Jun 18, 2024 at 7:50 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >
> > Robert Haas <robertmhaas@gmail.com> writes:
> > > On Tue, Jun 18, 2024 at 8:10 AM Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> > >> Executing below commands:
> > >> -- set allow_system_table_mods TO on;
> > >> -- truncate table pg_type;
> >
> > > If the operation isn't allowed without turning on
> > > allow_system_table_mods, that means that doing it is probably a bad
> > > idea and will probably break stuff, as happened here.
> >
> > Nothing good can come of truncating *any* core system catalog --- what
> > do you think you'll still be able to do afterwards?
> >
> > I think the assertion you noticed is there because the code path gets
> > traversed during REINDEX, which is an operation we do support on
> > system catalogs.  I have zero interest in making truncate work
> > on them.
> >
> 
> I agree with you on that point. How about considering a complete
> restriction instead?

What's the point?  There are occasional cases where doing something dangerous
is useful, for debugging or corruption recovery. If we flat out prohibit this
we'll just need a allow_system_table_mods_but_for_real option.

Greetings,

Andres Freund