Re: pg_basebackup failure after setting default_table_access_method option

> On Thu, Jun 6, 2019 at 9:06 AM Michael Paquier <michael@paquier.xyz> wrote:
>
> I was wondering if we actually need at all a catalog lookup at this
> stage, simplifying get_table_am_oid() on the way so as we always
> throw an error (its missing_ok is here to allow a proper error in the
> GUC context).

Just for me to understand, do you suggest to not check
default_table_access_method existence in check_default_table_access_method? If
yes, then

> The table AM lookup happens only when creating a table, so we could just get
> a failure when attempting to create a table with this incorrect value.

is correct, but doesn't it leave the room for some problems in the future with
a wrong assumptions about correctness of default_table_access_method?

> Actually, when updating a value and reloading and/or restarting the
> server, it is possible to easily get in a state where we have an
> invalid table AM parameter stored in the GUC, which is what the
> callback is here to avoid.  If you attempt to update the parameter
> with ALTER SYSTEM, then the command complains.  So it seems to me that
> the user experience is inconsistent.

Right, as far as I see the there is the same for e.g. default_tablespace due to
IsTransactionState condition. In fact looks like one can see the very same
issue with this option too, so probably it also needs to have MyDatabaseId
check.