Re: pg_walinspect: fix LSN validation messages and empty range handling

Hi Surya, Chao

>> PFA v4:
>>
>> * 0001 unchanged
>> * 0002 added the tests that Kiran suggested

Thanks for the review, Surya. I tested v4 on the same base
(e8a3ee5b197) and results are inline with your
findings

> 1. In subscription.sql, I don't think the session-authorization is needed.
> regress_subscription_user is created as LOGIN SUPERUSER at the top of the file and is the active role
> from line 190 onwards, so the session is already superuser when the new block runs.
> I removed the RESET/SET pair locally and the subscription test still passes, so the superuser bypass over
> pg_replication_origin_advance's restricted ACL is enough.
> Dropping them also keeps the new test running as the subscription owner, which is what every other SKIP test in the file does.

Agree on this!

> 2. The first comment in the new block looks misplaced:
> -- fail - LSN must not be behind the replication origin
> RESET SESSION AUTHORIZATION;
>
> RESET SESSION AUTHORIZATION neither fails nor has anything to do with the origin, and the comment duplicates the one further down above the statement it actually describes. I think it can just be removed.

Agree on this!

> 3. Still in that block, pg_replication_origin_advance() returns
> void, so its output is stable across runs and there is nothing for \gset to suppress. A plain terminated statement would read more naturally and wouldn't leave a psql variable behind.

Agree on 3. The \gset here is only hiding an empty one-row result, and
a plain statement says what it means. Worth noting it adds five lines to
the expected file, which seems a fair trade.

> 4. Very minor: the new WATCH_INTERVAL test uses
>
> '\set WATCH_INTERVAL 1000000' . "\n" . '\echo :WATCH_INTERVAL'
> where the surrounding tests in 001_basic.pl use a literal multiline single-quoted string.

Point 4 is my mistake, not Chao's. That concatenation came from the
snippet I sent upthread and he may have used it as-is. Sorry for the noise.

Thanks,
Kiran Kaki.