Re: Fix a server crash problem from pg_get_database_ddl

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