Re: corruption of WAL page header is never reported

Hello.

At Sun, 18 Jul 2021 04:55:05 +0900, Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp> wrote in
> Hello,
>
> I found that any corruption of WAL page header found during recovery is never
> reported in log messages. If wal page header is broken, it is detected in
> XLogReaderValidatePageHeader called from XLogPageRead, but the error messages
> are always reset and never reported.

Good catch! Currently recovery stops showing no reason if it is
stopped by page-header errors.

> I attached a patch to fix it in this way.

However, it is a kind of a roof-over-a-roof. What we should do is
just omitting the check in XLogPageRead while in standby mode.

> Or, if we wouldn't like to report an error for each check and also what we want
> to check here is just about old recycled WAL instead of header corruption itself,
> I wander that we could check just xlp_pageaddr instead of calling
> XLogReaderValidatePageHeader.

I'm not sure. But as described in the commit message, the commit
intended to save a common case and there's no obvious reason to (and
not to) restrict the check only to page address. So it uses the
established checking function.

I was tempted to adjust the comment just above by adding "while in
standby mode", but "so that we can retry immediately" is suggesting
that so I didn't do that in the attached.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center