Re: Fix a server crash problem from pg_get_database_ddl

Hi Chao,

On Sun, Apr 26, 2026 at 7:03 PM Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:

>
>
> > On Apr 26, 2026, at 22:50, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
> >
> >
> > On 2026-04-23 Th 2:47 AM, SATYANARAYANA NARLAPURAM wrote:
> >>
> >>
> >> Thanks for printing out that. Yes, they are similar.
> >>
> >> I agree with what Tom said in [2]:
> >> ```
> >> This is not a bug. This is a superuser intentionally breaking
> >> the system by corrupting the catalogs. There are any number
> >> of ways to cause trouble with ill-advised manual updates to a
> >> catalog table. Try, eg, "DELETE FROM pg_proc" (... but not in
> >> a database you care about).
> >> ```
> >>
> >> So, let me take back this patch.
> >>
> >> [2]
> https://www.postgresql.org/message-id/1538113.1768921841@sss.pgh.pa.us
> >> In this case, it is a very corner case but not something superuser
> intentionally breaks.
> >> For example, a concurrent tablespace drop + database ddl to assign a
> different tablespace or default.
> >> We aren't acquiring Access Share lock on the DB in this function
> (intentional) so it is a good practice
> >> to do the null checks. Of course, it makes more sense to add this
> comment while doing a code review.
> >> I will let Tom and others chime in with their thoughts on fixing this.
> >>
> >> Attached an injection point test to show the race. Not intended to
> commit.
> >>
> >>
> >
> > I agree if there's a race condition we should protect against it. I
> don't much like the idea of silently ignoring it, though. Raising an error
> seems more like the right thing to do.
> >
> > cheers
> >
> > andrew
> > --
> > Andrew Dunstan
> > EDB: https://www.enterprisedb.com
> >
>
> The v1 patch raises an error when the tablespace name is NULL.
>
> PFA v2: removed hint from the error message, because I now consider the
> hint might not be necessary.
>

+ if (spcname == NULL)
+ ereport(ERROR,
+ errcode(ERRCODE_UNDEFINED_OBJECT),
+ errmsg("tablespace with OID %u does not exist",
+ dbform->dattablespace));
+

A message with error detail that says a concurrent DDL could have dropped a
tablespace could be better?
System catalog is optional.
Something like:

errdetail("The tablespace may have been dropped concurrently, or the system
catalog is inconsistent.")));

Thanks,
Satya