Function pop

fdbserver/BackupWorker.actor.cpp:317–334

	}

	void pop() {
		if (backupEpoch > oldestBackupEpoch || stopped) {
			// Defer pop if old epoch hasn't finished popping yet.
			// If stopped because of displacement, do NOT pop as the progress may
			// not be saved in a timely fashion. As a result, next epoch may still
			// need to read mutations in the version range. Let the next epoch's
			// worker do the pop instead.
			TraceEvent("BackupWorkerPopDeferred", myId)
			    .suppressFor(1.0)
			    .detail("BackupEpoch", backupEpoch)
			    .detail("OldestEpoch", oldestBackupEpoch)
			    .detail("Version", savedVersion);
			return;
		}
		ASSERT_WE_THINK(backupEpoch == oldestBackupEpoch);
		const Tag popTag = logSystem.get()->getPseudoPopTag(tag, ProcessClass::BackupClass);
		logSystem.get()->pop(std::max(popVersion, savedVersion), popTag);
	}

	void stop() {
		stopped = true;