[v3.4] Fix issue15271

mvcc/watchable_store.go

@@ -459,7 +459,6 @@ func (s *watchableStore) notify(rev int64, evs []mvccpb.Event) {
 			pendingEventsGauge.Add(float64(len(eb.evs)))
 		} else {
 			// move slow watcher to victims
-			w.minRev = rev + 1
 			if victim == nil {
 				victim = make(watcherBatch)
 			}
@@ -468,6 +467,10 @@ func (s *watchableStore) notify(rev int64, evs []mvccpb.Event) {
 			s.synced.delete(w)
 			slowWatcherGauge.Inc()
 		}
+		// always update minRev
+		// in case 'send' returns true and watcher stays synced, this is needed for Restore when all watchers become unsynced
+		// in case 'send' returns false, this is needed for syncWatchers
+		w.minRev = rev + 1
 	}
 	s.addVictim(victim)
 }

mvcc/watchable_store_test.go

@@ -307,39 +307,40 @@ func TestWatchRestore(t *testing.T) {
 
 			testKey := []byte("foo")
 			testValue := []byte("bar")
-			rev := s.Put(testKey, testValue, lease.NoLease)
-
-			newBackend, newPath := backend.NewDefaultTmpBackend()
-			newStore := newWatchableStore(zap.NewExample(), newBackend, &lease.FakeLessor{}, nil, nil, StoreConfig{})
-			defer cleanup(newStore, newBackend, newPath)
-
-			w := newStore.NewWatchStream()
-			w.Watch(0, testKey, nil, rev-1)
+			w := s.NewWatchStream()
+			defer w.Close()
+			w.Watch(0, testKey, nil, 1)
 
 			time.Sleep(delay)
+			wantRev := s.Put(testKey, testValue, lease.NoLease)
 
-			newStore.Restore(b)
-			select {
-			case resp := <-w.Chan():
-				if resp.Revision != rev {
-					t.Fatalf("rev = %d, want %d", resp.Revision, rev)
-				}
-				if len(resp.Events) != 1 {
-					t.Fatalf("failed to get events from the response")
-				}
-				if resp.Events[0].Kv.ModRevision != rev {
-					t.Fatalf("kv.rev = %d, want %d", resp.Events[0].Kv.ModRevision, rev)
-				}
-			case <-time.After(time.Second):
-				t.Fatal("failed to receive event in 1 second.")
+			s.Restore(b)
+			events := readEventsForSecond(w.Chan())
+			if len(events) != 1 {
+				t.Errorf("Expected only one event, got %d", len(events))
+			}
+			if events[0].Kv.ModRevision != wantRev {
+				t.Errorf("Expected revision to match, got %d, want %d", events[0].Kv.ModRevision, wantRev)
 			}
+
 		}
 	}
 
 	t.Run("Normal", test(0))
 	t.Run("RunSyncWatchLoopBeforeRestore", test(time.Millisecond*120)) // longer than default waitDuration
 }
 
+func readEventsForSecond(ws <-chan WatchResponse) (events []mvccpb.Event) {
+	for {
+		select {
+		case resp := <-ws:
+			events = append(events, resp.Events...)
+		case <-time.After(time.Second):
+			return events
+		}
+	}
+}
+
 // TestWatchRestoreSyncedWatcher tests such a case that:
 //  1. watcher is created with a future revision "math.MaxInt64 - 2"
 //  2. watcher with a future revision is added to "synced" watcher group