Re: standby promotion can create unreadable WAL

On Fri, Aug 26, 2022 at 8:44 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> ArchiveRecoveryRequested is true.  So in the below check[1] instead of
> (!StandbyMode), we can just put (! ArchiveRecoveryRequested), and then
> we don't need any other fix.  Am I missing anything?
>
> [1]
> ReadRecord{
> ..record = XLogPrefetcherReadRecord(xlogprefetcher, &errormsg);
>         if (record == NULL)
>         {
>             /*
>              * When not in standby mode we find that WAL ends in an incomplete
>              * record, keep track of that record.  After recovery is done,
>              * we’ll write a record to indicate to downstream WAL readers that
>              * that portion is to be ignored.
>              */
>             if (!StandbyMode &&
>                 !XLogRecPtrIsInvalid(xlogreader->abortedRecPtr))
>             {
>                 abortedRecPtr = xlogreader->abortedRecPtr;
>                 missingContrecPtr = xlogreader->missingContrecPtr;
>             }

I agree. Testing StandbyMode here seems bogus. I thought initially
that the test should perhaps be for InArchiveRecovery rather than
ArchiveRecoveryRequested, but I see that the code which switches to a
new timeline cares about ArchiveRecoveryRequested, so I think that is
the correct thing to test here as well.

Concretely, I propose the following patch.

--
Robert Haas
EDB: http://www.enterprisedb.com