Fix query request lost bug (#7715)

Issue: #7633
Signed-off-by: sunby <bingyi.sun@zilliz.com>

internal/querynode/query_collection.go

@@ -165,9 +165,10 @@ func (q *queryCollection) addToUnsolvedMsg(msg queryMsg) {
 func (q *queryCollection) popAllUnsolvedMsg() []queryMsg {
 	q.unsolvedMsgMu.Lock()
 	defer q.unsolvedMsgMu.Unlock()
-	tmp := q.unsolvedMsg
+	ret := make([]queryMsg, 0, len(q.unsolvedMsg))
+	ret = append(ret, q.unsolvedMsg...)
 	q.unsolvedMsg = q.unsolvedMsg[:0]
-	return tmp
+	return ret
 }
 
 func (q *queryCollection) waitNewTSafe() Timestamp {

internal/querynode/query_collection_test.go

@@ -447,3 +447,36 @@ func TestResultHandlerStage_TranslateHits(t *testing.T) {
 		assert.Error(t, err)
 	})
 }
+
+func TestQueryCollection_AddPopUnsolvedMsg(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.TODO())
+	qCollection, err := genSimpleQueryCollection(ctx, cancel)
+	assert.Nil(t, err)
+	var i int64
+	for i = 0; i < 3; i++ {
+		qCollection.addToUnsolvedMsg(&msgstream.RetrieveMsg{
+			RetrieveRequest: internalpb.RetrieveRequest{
+				Base: &commonpb.MsgBase{MsgID: i},
+			},
+		})
+	}
+
+	unsolved := qCollection.popAllUnsolvedMsg()
+	assert.EqualValues(t, 3, len(unsolved))
+	for i := 0; i < 3; i++ {
+		assert.EqualValues(t, i, unsolved[i].ID())
+	}
+
+	// add new msg to unsolved msgs and check old unsolved msg
+	for i := 0; i < 3; i++ {
+		qCollection.addToUnsolvedMsg(&msgstream.RetrieveMsg{
+			RetrieveRequest: internalpb.RetrieveRequest{
+				Base: &commonpb.MsgBase{MsgID: 4},
+			},
+		})
+	}
+
+	for i := 0; i < 3; i++ {
+		assert.EqualValues(t, i, unsolved[i].ID())
+	}
+}