*: refine non-global stale-read request retry logic (#851)

internal/locate/region_request.go

@@ -532,12 +532,12 @@ func (state *tryNewProxy) onNoLeader(selector *replicaSelector) {
 type accessFollower struct {
 	stateBase
 	// If tryLeader is true, the request can also be sent to the leader when !leader.isSlow()
-	tryLeader         bool
-	isGlobalStaleRead bool
-	option            storeSelectorOp
-	leaderIdx         AccessIndex
-	lastIdx           AccessIndex
-	learnerOnly       bool
+	tryLeader   bool
+	isStaleRead bool
+	option      storeSelectorOp
+	leaderIdx   AccessIndex
+	lastIdx     AccessIndex
+	learnerOnly bool
 }
 
 func (state *accessFollower) next(bo *retry.Backoffer, selector *replicaSelector) (*RPCContext, error) {
@@ -558,12 +558,10 @@ func (state *accessFollower) next(bo *retry.Backoffer, selector *replicaSelector
 			}
 		}
 	} else {
-		// Stale Read request will retry the leader or next peer on error,
-		// if txnScope is global, we will only retry the leader by using the WithLeaderOnly option,
-		// if txnScope is local, we will retry both other peers and the leader by the strategy of replicaSelector.
-		if state.isGlobalStaleRead {
+		// Stale Read request will retry the leader only by using the WithLeaderOnly option,
+		if state.isStaleRead {
 			WithLeaderOnly()(&state.option)
-			// retry on the leader should not use stale read flag to avoid possible DataIsNotReady error as it always can serve any read
+			// retry on the leader should not use stale read flag to avoid possible DataIsNotReady error as it always can serve any read.
 			resetStaleRead = true
 		}
 		state.lastIdx++
@@ -766,12 +764,12 @@ func newReplicaSelector(
 		}
 		tryLeader := req.ReplicaReadType == kv.ReplicaReadMixed || req.ReplicaReadType == kv.ReplicaReadPreferLeader
 		state = &accessFollower{
-			tryLeader:         tryLeader,
-			isGlobalStaleRead: req.IsGlobalStaleRead(),
-			option:            option,
-			leaderIdx:         regionStore.workTiKVIdx,
-			lastIdx:           -1,
-			learnerOnly:       req.ReplicaReadType == kv.ReplicaReadLearner,
+			tryLeader:   tryLeader,
+			isStaleRead: req.StaleRead,
+			option:      option,
+			leaderIdx:   regionStore.workTiKVIdx,
+			lastIdx:     -1,
+			learnerOnly: req.ReplicaReadType == kv.ReplicaReadLearner,
 		}
 	}
 

internal/locate/region_request_test.go

@@ -657,3 +657,39 @@ func (s *testRegionRequestToSingleStoreSuite) TestCloseConnectionOnStoreNotMatch
 	s.NotNil(regionErr)
 	s.Equal(target, client.closedAddr)
 }
+
+func (s *testRegionRequestToSingleStoreSuite) TestStaleReadRetry() {
+	req := tikvrpc.NewRequest(tikvrpc.CmdGet, &kvrpcpb.GetRequest{
+		Key: []byte("key"),
+	})
+	req.EnableStaleRead()
+	req.ReadReplicaScope = "z1" // not global stale read.
+	region, err := s.cache.LocateRegionByID(s.bo, s.region)
+	s.Nil(err)
+	s.NotNil(region)
+
+	oc := s.regionRequestSender.client
+	defer func() {
+		s.regionRequestSender.client = oc
+	}()
+
+	s.regionRequestSender.client = &fnClient{fn: func(ctx context.Context, addr string, req *tikvrpc.Request, timeout time.Duration) (response *tikvrpc.Response, err error) {
+		if req.StaleRead {
+			// Mock for stale-read request always return DataIsNotReady error when tikv `ResolvedTS` is blocked.
+			response = &tikvrpc.Response{Resp: &kvrpcpb.GetResponse{
+				RegionError: &errorpb.Error{DataIsNotReady: &errorpb.DataIsNotReady{}},
+			}}
+		} else {
+			response = &tikvrpc.Response{Resp: &kvrpcpb.GetResponse{Value: []byte("value")}}
+		}
+		return response, nil
+	}}
+
+	bo := retry.NewBackofferWithVars(context.Background(), 5, nil)
+	resp, _, err := s.regionRequestSender.SendReq(bo, req, region.Region, time.Second)
+	s.Nil(err)
+	s.NotNil(resp)
+	regionErr, _ := resp.GetRegionError()
+	s.Nil(regionErr)
+	s.Equal([]byte("value"), resp.Resp.(*kvrpcpb.GetResponse).Value)
+}