Add datacoord Server comment and improve para (#6182)

Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>

internal/datacoord/cluster.go

@@ -133,10 +133,13 @@ func (c *cluster) refresh(dataNodes []*datapb.DataNodeInfo) error {
 }
 
 // paraRun parallel run, with max Parallel limit
-func parraRun(works []func(), maxRunner int) {
+func paraRun(works []func(), maxRunner int) {
 	wg := sync.WaitGroup{}
 	ch := make(chan func())
 	wg.Add(len(works))
+	if maxRunner > len(works) {
+		maxRunner = len(works)
+	}
 
 	for i := 0; i < maxRunner; i++ {
 		go func() {
@@ -210,6 +213,7 @@ func (c *cluster) watch(nodes []*datapb.DataNodeInfo) ([]*datapb.DataNodeInfo, e
 				mut.Lock()
 				errs = append(errs, err)
 				mut.Unlock()
+				return
 			}
 			if resp.ErrorCode != commonpb.ErrorCode_Success {
 				log.Warn("watch channels failed", zap.String("address", n.Address), zap.Error(err))
@@ -225,8 +229,11 @@ func (c *cluster) watch(nodes []*datapb.DataNodeInfo) ([]*datapb.DataNodeInfo, e
 			}
 		})
 	}
-	parraRun(works, 3)
+	paraRun(works, 20)
-	return nodes, retry.ErrorList(errs)
+	if len(errs) > 0 {
+		return nodes, retry.ErrorList(errs)
+	}
+	return nodes, nil
 }
 
 func (c *cluster) register(n *datapb.DataNodeInfo) {

internal/datacoord/grpc_services.go

@@ -19,7 +19,7 @@ import (
 const serverNotServingErrMsg = "server is not serving"
 
 func (s *Server) isClosed() bool {
-	return atomic.LoadInt64(&s.isServing) != 2
+	return atomic.LoadInt64(&s.isServing) != ServerStateHealthy
 }
 
 func (s *Server) GetTimeTickChannel(ctx context.Context) (*milvuspb.StringResponse, error) {
@@ -354,9 +354,9 @@ func (s *Server) GetComponentStates(ctx context.Context) (*internalpb.ComponentS
 	}
 	state := atomic.LoadInt64(&s.isServing)
 	switch state {
-	case 1:
+	case ServerStateInitializing:
 		resp.State.StateCode = internalpb.StateCode_Initializing
-	case 2:
+	case ServerStateHealthy:
 		resp.State.StateCode = internalpb.StateCode_Healthy
 	default:
 		resp.State.StateCode = internalpb.StateCode_Abnormal

internal/datacoord/server.go

@@ -48,15 +48,29 @@ type (
 	Timestamp = typeutil.Timestamp
 )
 
+// ServerState type alias
+type ServerState = int64
+
+const (
+	// ServerStateStopped state stands for just created or stopped `Server` instance
+	ServerStateStopped ServerState = 0
+	// ServerStateInitializing state stands initializing `Server` instance
+	ServerStateInitializing ServerState = 1
+	// ServerStateHealthy state stands for healthy `Server` instance
+	ServerStateHealthy ServerState = 2
+)
+
 type dataNodeCreatorFunc func(ctx context.Context, addr string) (types.DataNode, error)
 type rootCoordCreatorFunc func(ctx context.Context, metaRootPath string, etcdEndpoints []string) (types.RootCoord, error)
 
+// Server implements `types.Datacoord`
+// handles Data Cooridinator related jobs
 type Server struct {
 	ctx              context.Context
 	serverLoopCtx    context.Context
 	serverLoopCancel context.CancelFunc
 	serverLoopWg     sync.WaitGroup
-	isServing        int64
+	isServing        ServerState
 
 	kvClient          *etcdkv.EtcdKV
 	meta              *meta
@@ -79,6 +93,7 @@ type Server struct {
 	rootCoordClientCreator rootCoordCreatorFunc
 }
 
+// CreateServer create `Server` instance
 func CreateServer(ctx context.Context, factory msgstream.Factory) (*Server, error) {
 	rand.Seed(time.Now().UnixNano())
 	s := &Server{
@@ -107,11 +122,19 @@ func (s *Server) Register() error {
 	return nil
 }
 
+// Init change server state to Initializing
 func (s *Server) Init() error {
-	atomic.StoreInt64(&s.isServing, 1)
+	atomic.StoreInt64(&s.isServing, ServerStateInitializing)
 	return nil
 }
 
+// Start initialize `Server` members and start loops, follow steps are taken:
+// 1. initialize message factory parameters
+// 2. initialize root coord client, meta, datanode cluster, segment info channel,
+//		allocator, segment manager
+// 3. start service discovery and server loops, which includes message stream handler (segment statistics,datanode tt)
+//		datanodes etcd watch, etcd alive check and flush completed status check
+// 4. set server state to Healthy
 func (s *Server) Start() error {
 	var err error
 	m := map[string]interface{}{
@@ -151,7 +174,7 @@ func (s *Server) Start() error {
 
 	s.startServerLoop()
 
-	atomic.StoreInt64(&s.isServing, 2)
+	atomic.StoreInt64(&s.isServing, ServerStateHealthy)
 	log.Debug("DataCoordinator startup success")
 	return nil
 }
@@ -482,12 +505,16 @@ func (s *Server) initRootCoordClient() error {
 	return s.rootCoordClient.Start()
 }
 
+// Stop do the Server finalize processes
+// it checks the server status is healthy, if not, just quit
+// if Server is healthy, set server state to stopped, release etcd session,
+//	stop message stream client and stop server loops
 func (s *Server) Stop() error {
-	if !atomic.CompareAndSwapInt64(&s.isServing, 2, 0) {
+	if !atomic.CompareAndSwapInt64(&s.isServing, ServerStateHealthy, ServerStateStopped) {
 		return nil
 	}
 	log.Debug("DataCoord server shutdown")
-	atomic.StoreInt64(&s.isServing, 0)
+	atomic.StoreInt64(&s.isServing, ServerStateStopped)
 	s.cluster.releaseSessions()
 	s.segmentInfoStream.Close()
 	s.flushMsgStream.Close()