Re: standby promotion can create unreadable WAL

On Fri, Aug 26, 2022 at 8:44 AM Dilip Kumar <dilipbalaut(at)gmail(dot)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