wal: send watch events only when needed

internal/wal/wal.go

@@ -480,6 +480,7 @@ func (w *WalManager) Watch(ctx context.Context, revision int64) <-chan *WatchEle
 		defer close(walCh)
 		for wresp := range wch {
 			we := &WatchElement{ChangeGroupsRevisions: make(changeGroupsRevisions)}
+			send := false
 
 			if wresp.Canceled {
 				err := wresp.Err()
@@ -501,6 +502,7 @@ func (w *WalManager) Watch(ctx context.Context, revision int64) <-chan *WatchEle
 
 				switch {
 				case strings.HasPrefix(key, etcdWalsDir+"/"):
+					send = true
 					switch ev.Type {
 					case mvccpb.PUT:
 						var walData *WalData
@@ -514,6 +516,7 @@ func (w *WalManager) Watch(ctx context.Context, revision int64) <-chan *WatchEle
 					}
 
 				case strings.HasPrefix(key, etcdChangeGroupsDir+"/"):
+					send = true
 					switch ev.Type {
 					case mvccpb.PUT:
 						changeGroup := path.Base(string(ev.Kv.Key))
@@ -523,13 +526,18 @@ func (w *WalManager) Watch(ctx context.Context, revision int64) <-chan *WatchEle
 						we.ChangeGroupsRevisions[changeGroup] = 0
 					}
 
+				case key == etcdPingKey:
+					send = true
+
 				default:
 					continue
 				}
 			}
 
+			if send {
 				walCh <- we
 			}
+		}
 	}()
 
 	return walCh