Re: Improve error context after some failed XLogReadRecord()

At Tue, 9 Nov 2021 10:47:11 +0900, Michael Paquier <michael(at)paquier(dot)xyz> wrote in
> Hi all,
>
> I have noticed $subject while looking at a patch in this area:
> https://www.postgresql.org/message-id/YYiqxtEqhgb5gIWL@paquier.xyz
>
> While we don't expect the four callers of XLogReadRecord() related to
> logical decoding to fail in the code paths changed by the patch
> attached, I think that it would be good to provide more context to
> users rather than just emitting an elog(ERROR) coming directly from
> the WAL reader. This way, it becomes a bit easier to guess from where
> the failure is coming.
>
> A patch is attached to improve all those elog()s. I have tried not to
> be too fancy about those new error strings, but I am sure that these
> could be tweaked.
>
> Thoughts?

As the whole, I agree that any substantial message is far better than
"%s" in regard to identifying the line that emitted a log line.

+ elog(ERROR, "could not find record to advance replication slot: %s",

I prefer "could not read record while advancing replcation slot",
because it is not finding a record but it is reading successive
records. However, I don't strongly object to the current wording.

+ elog(ERROR, "could not find record to send logically-decoded data: %s", errm);

I prefer something like the above for the same reason. How about
"could not read record while sending logically-decoded data:". The
same with above, I'm not strongly opposed to the current wording.

Otherwise it looks good to me.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center