avoid dataIsNotReady error while retrying stale read on the leader

Signed-off-by: artem_danilov <artem_danilov@airbnb.com>

internal/locate/region_request.go

@@ -1194,6 +1194,12 @@ func (s *RegionRequestSender) SendReqCtx(
 			}
 		}
 
+		if retryTimes > 0 && s.replicaSelector != nil && s.replicaSelector.regionStore != nil &&
+			s.replicaSelector.targetIdx == s.replicaSelector.regionStore.workTiKVIdx {
+			// retry on the leader should not use stale read to avoid possible DataIsNotReady error as it always can serve any read
+			req.StaleRead = false
+		}
+
 		var retry bool
 		resp, retry, err = s.sendReqToRegion(bo, rpcCtx, req, timeout)
 		if err != nil {

internal/locate/region_request3_test.go

@@ -909,8 +909,8 @@ func (s *testRegionRequestToThreeStoresSuite) TestSendReqWithReplicaSelector() {
 	req = tikvrpc.NewRequest(tikvrpc.CmdGet, &kvrpcpb.GetRequest{Key: []byte("key")})
 	req.ReadReplicaScope = oracle.GlobalTxnScope
 	req.TxnScope = oracle.GlobalTxnScope
-	req.EnableStaleRead()
 	for i := 0; i < 5; i++ {
+		req.EnableStaleRead()
 		// The request may be sent to the leader directly. We have to distinguish it.
 		failureOnFollower := false
 		s.regionRequestSender.client = &fnClient{fn: func(ctx context.Context, addr string, req *tikvrpc.Request, timeout time.Duration) (response *tikvrpc.Response, err error) {
@@ -929,6 +929,13 @@ func (s *testRegionRequestToThreeStoresSuite) TestSendReqWithReplicaSelector() {
 			totalAttempts += replica.attempts
 			if idx == int(state.leaderIdx) {
 				s.Equal(1, replica.attempts)
+				if failureOnFollower {
+					// retry always goes to the leader as an ordinary read,not a stale one
+					s.True(!req.StaleRead)
+				} else {
+					// if the first request goes directly to the leader then it keeps stale read flag
+					s.True(req.StaleRead)
+				}
 			} else {
 				s.True(replica.attempts <= 1)
 			}