On Sun, Oct 09, 2022 at 02:39:47PM +0530, Bharath Rupireddy wrote: > We can give it a chance to restore from pg_wal before switching to > streaming to not change any behaviour of the state machine. But, not > definitely by setting currentSource to XLOG_FROM_WAL, we basically > never explicitly set currentSource to XLOG_FROM_WAL, other than when > not in archive recovery i.e. InArchiveRecovery is false. Also, see the > comment [1]. > > Instead, the simplest would be to just pass XLOG_FROM_WAL to > XLogFileReadAnyTLI() when we're about to switch the source to stream > mode. This doesn't change the existing behaviour.
It might be more consistent with existing behavior, but one thing I hadn't considered is that it might make your proposed feature ineffective when users are copying files straight into pg_wal. IIUC as long as the files are present in pg_wal, the source-switch logic won't kick in. > Unrelated to this patch, the fact that the standby polls pg_wal is not > documented or recommended, is not true, it is actually documented [2]. > Whether or not we change the docs to be something like [3], is a > separate discussion. I wonder if it would be better to simply remove this extra polling of pg_wal as a prerequisite to your patch. The existing commentary leads me to think there might not be a strong reason for this behavior, so it could be a nice way to simplify your patch. -- Nathan Bossart Amazon Web Services: https://aws.amazon.com