mvcc/watchable_store.go
func (s *watchableStore) moveVictims() (moved int) {
	s.mu.Lock()
	victims := s.victims
	s.victims = nil
	s.mu.Unlock()

	var newVictim watcherBatch
	for _, wb := range victims {
		// try to send responses again
		for w, eb := range wb {
			// watcher has observed the store up to, but not including, w.minRev
			rev := w.minRev - 1
			if w.send(WatchResponse{WatchID: w.id, Events: eb.evs, Revision: rev}) {
				pendingEventsGauge.Add(float64(len(eb.evs)))
			} else {
				if newVictim == nil {
					newVictim = make(watcherBatch)
				}
				newVictim[w] = eb
				continue
			}
			moved++
		}

		// assign completed victim watchers to unsync/sync
		s.mu.Lock()
		s.store.revMu.RLock()
		curRev := s.store.currentRev
		for w, eb := range wb {
			if newVictim != nil && newVictim[w] != nil {
				// couldn't send watch response; stays victim
				continue
			}
			w.victim = false
			if eb.moreRev != 0 {
				w.minRev = eb.moreRev
			}
			if w.minRev <= curRev {
				s.unsynced.add(w)
			} else {
				slowWatcherGauge.Dec()
				s.synced.add(w)
			}
		}
		s.store.revMu.RUnlock()
		s.mu.Unlock()
	}

	if len(newVictim) > 0 {
		s.mu.Lock()
		s.victims = append(s.victims, newVictim)
		s.mu.Unlock()
	}

	return moved
}
func (s *watchableStore) moveVictims() (moved int) {
	s.mu.Lock()
	victims := s.victims
	s.victims = nil
	s.mu.Unlock()

	var newVictim watcherBatch
	for _, wb := range victims {
		// try to send responses again
		for w, eb := range wb {
			// watcher has observed the store up to, but not including, w.minRev
			rev := w.minRev - 1
			if w.send(WatchResponse{WatchID: w.id, Events: eb.evs, Revision: rev}) {
				pendingEventsGauge.Add(float64(len(eb.evs)))
			} else {
				if newVictim == nil {
					newVictim = make(watcherBatch)
				}
				newVictim[w] = eb
				continue
			}
			moved++
		}

		// assign completed victim watchers to unsync/sync
		s.mu.Lock()
		s.store.revMu.RLock()
		curRev := s.store.currentRev
		for w, eb := range wb {
			if newVictim != nil && newVictim[w] != nil {
				// couldn't send watch response; stays victim
				continue
			}
			w.victim = false
			if eb.moreRev != 0 {
				w.minRev = eb.moreRev
			}
			if w.minRev <= curRev {
				s.unsynced.add(w)
			} else {
				slowWatcherGauge.Dec()
				s.synced.add(w)
			}
		}
		s.store.revMu.RUnlock()
		s.mu.Unlock()
	}

	if len(newVictim) > 0 {
		s.mu.Lock()
		s.victims = append(s.victims, newVictim)
		s.mu.Unlock()
	}

	return moved
}
// moveVictims tries to update watches with already pending event data