etcdserver: skip range requests in txn if the result is needless

If a server isn't serving txn requests from a client, the server
doesn't need the result of range requests in the txn.

This is a succeeding commit of
#5689

etcdserver/apply.go

@@ -360,6 +360,11 @@ func (a *applierV3backend) Txn(rt *pb.TxnRequest) (*pb.TxnResponse, error) {
 	resps := make([]*pb.ResponseOp, len(reqs))
 	changedKV := false
 	for i := range reqs {
+		if reqs[i] == nil {
+			// removed by removeNeedlessRangeReqs()
+			continue
+		}
+
 		if reqs[i].GetRequestRange() == nil {
 			changedKV = true
 		}
@@ -732,6 +737,11 @@ func (s *kvSortByValue) Less(i, j int) bool {
 
 func (a *applierV3backend) checkRequestLeases(reqs []*pb.RequestOp) error {
 	for _, requ := range reqs {
+		if requ == nil {
+			// removed by removeNeedlessRangeReqs()
+			continue
+		}
+
 		tv, ok := requ.Request.(*pb.RequestOp_RequestPut)
 		if !ok {
 			continue
@@ -749,6 +759,11 @@ func (a *applierV3backend) checkRequestLeases(reqs []*pb.RequestOp) error {
 
 func (a *applierV3backend) checkRequestRange(reqs []*pb.RequestOp) error {
 	for _, requ := range reqs {
+		if requ == nil {
+			// removed by removeNeedlessRangeReqs()
+			continue
+		}
+
 		tv, ok := requ.Request.(*pb.RequestOp_RequestRange)
 		if !ok {
 			continue
@@ -788,3 +803,17 @@ func isGteRange(rangeEnd []byte) bool {
 func noSideEffect(r *pb.InternalRaftRequest) bool {
 	return r.Range != nil || r.AuthUserGet != nil || r.AuthRoleGet != nil
 }
+
+func removeNeedlessRangeReqs(txn *pb.TxnRequest) {
+	f := func(ops []*pb.RequestOp) {
+		for i := 0; i < len(ops); i++ {
+			switch ops[i].Request.(type) {
+			case *pb.RequestOp_RequestRange:
+				ops[i] = nil
+			}
+		}
+	}
+
+	f(txn.Success)
+	f(txn.Failure)
+}

etcdserver/apply_auth.go

@@ -94,6 +94,11 @@ func (aa *authApplierV3) DeleteRange(txnID int64, r *pb.DeleteRangeRequest) (*pb
 
 func (aa *authApplierV3) checkTxnReqsPermission(reqs []*pb.RequestOp) error {
 	for _, requ := range reqs {
+		if requ == nil {
+			// removed by removeNeedlessRangeReqs()
+			continue
+		}
+
 		switch tv := requ.Request.(type) {
 		case *pb.RequestOp_RequestRange:
 			if tv.RequestRange == nil {

etcdserver/server.go

@@ -1080,7 +1080,11 @@ func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry) {
 	}
 
 	var ar *applyResult
-	if s.w.IsRegistered(id) || !noSideEffect(&raftReq) {
+	needResult := s.w.IsRegistered(id)
+	if needResult || !noSideEffect(&raftReq) {
+		if !needResult && raftReq.Txn != nil {
+			removeNeedlessRangeReqs(raftReq.Txn)
+		}
 		ar = s.applyV3.Apply(&raftReq)
 	}