Re: Database-level collation version tracking

On 08.02.22 13:55, Julien Rouhaud wrote:
> I'm just saying that without such a lock you can easily trigger the "cache
> lookup" error, and that's something that's supposed to happen with normal
> usage I think. So it should be a better message saying that the database has
> been concurrently dropped, or actually simply does not exist like it's done in
> AlterDatabaseOwner() for the same pattern:
>
> [...]
> tuple = systable_getnext(scan);
> if (!HeapTupleIsValid(tuple))
> ereport(ERROR,
> (errcode(ERRCODE_UNDEFINED_DATABASE),
> errmsg("database \"%s\" does not exist", dbname)));
> [...]

In my code, the existence of the database is checked by

dboid = get_database_oid(stmt->dbname, false);

This also issues an appropriate user-facing error message if the
database does not exist.

The flow in AlterDatabaseOwner() is a bit different, it looks up the
pg_database tuple directly from the name. I think both are correct. My
code has been copied from the analogous code in AlterCollation().