Re: BUG #8686: Standby could not restart.

                /*
                 * Initialize shared replayEndRecPtr, lastReplayedEndRecPtr, and
                 * recoveryLastXTime.
                 *
                 * This is slightly confusing if we're starting from an online
                 * checkpoint; we've just read and replayed the checkpoint record, but
                 * we're going to start replay from its redo pointer, which precedes
                 * the location of the checkpoint record itself. So even though the
                 * last record we've replayed is indeed ReadRecPtr, we haven't
                 * replayed all the preceding records yet. That's OK for the current
                 * use of these variables.
                 */
                SpinLockAcquire(&xlogctl->info_lck);
                xlogctl->replayEndRecPtr = ReadRecPtr;
                xlogctl->lastReplayedEndRecPtr = EndRecPtr;
                xlogctl->recoveryLastXTime = 0;
                xlogctl->currentChunkStartTime = 0;
                xlogctl->recoveryPause = false;
                SpinLockRelease(&xlogctl->info_lck);

I think we need to fix that confusion. Your patch will do it by not setting EndRecPtr yet; that fixes the bug, but leaves those variables in a slightly strange state; I'm not sure what EndRecPtr points to in that case (0 ?), but ReadRecPtr would be set I guess.

Perhaps we should reset replayEndRecPtr and lastReplayedEndRecPtr to the REDO point here, instead of ReadRecPtr/EndRecPtr.