fix balance channel (#23631)

Signed-off-by: Wei Liu <wei.liu@zilliz.com>

internal/querycoordv2/balance/rowcount_based_balancer.go

@@ -267,24 +267,30 @@ func (b *RowCountBasedBalancer) genChannelPlan(replica *meta.Replica, onlineNode
 		}
 
 		for start < end {
-			sourceNode := nodes[start]
-			targetNode := nodes[end]
+			// segment to move in
+			targetNode := nodes[start]
+			// segment to move out
+			sourceNode := nodes[end]
+
+			if len(channelsOnNode[targetNode]) >= averageChannel {
+				break
+			}
 
 			// remove channel from end node
-			selectChannel := channelsOnNode[targetNode][0]
-			channelsOnNode[targetNode] = channelsOnNode[targetNode][1:]
+			selectChannel := channelsOnNode[sourceNode][0]
+			channelsOnNode[sourceNode] = channelsOnNode[sourceNode][1:]
 
 			// add channel to start node
-			if channelsOnNode[sourceNode] == nil {
-				channelsOnNode[sourceNode] = make([]*meta.DmChannel, 0)
+			if channelsOnNode[targetNode] == nil {
+				channelsOnNode[targetNode] = make([]*meta.DmChannel, 0)
 			}
-			channelsOnNode[sourceNode] = append(channelsOnNode[sourceNode], selectChannel)
+			channelsOnNode[targetNode] = append(channelsOnNode[targetNode], selectChannel)
 
 			// generate channel plan
 			plan := ChannelAssignPlan{
 				Channel:   selectChannel,
-				From:      targetNode,
-				To:        sourceNode,
+				From:      sourceNode,
+				To:        targetNode,
 				ReplicaID: replica.ID,
 			}
 			channelPlans = append(channelPlans, plan)

internal/querycoordv2/balance/rowcount_based_balancer_test.go

@@ -272,6 +272,28 @@ func (suite *RowCountBasedBalancerTestSuite) TestBalance() {
 				{Channel: &meta.DmChannel{VchannelInfo: &datapb.VchannelInfo{CollectionID: 1, ChannelName: "v2"}, Node: 2}, From: 2, To: 3, ReplicaID: 1},
 			},
 		},
+		{
+			name:          "unbalance stable view",
+			nodes:         []int64{1, 2, 3},
+			segmentCnts:   []int{0, 0, 0},
+			states:        []session.State{session.NodeStateNormal, session.NodeStateNormal, session.NodeStateNormal},
+			shouldMock:    true,
+			distributions: map[int64][]*meta.Segment{},
+			distributionChannels: map[int64][]*meta.DmChannel{
+				1: {
+					{VchannelInfo: &datapb.VchannelInfo{CollectionID: 1, ChannelName: "v1"}, Node: 2},
+					{VchannelInfo: &datapb.VchannelInfo{CollectionID: 1, ChannelName: "v2"}, Node: 2},
+				},
+				2: {
+					{VchannelInfo: &datapb.VchannelInfo{CollectionID: 1, ChannelName: "v3"}, Node: 2},
+				},
+				3: {
+					{VchannelInfo: &datapb.VchannelInfo{CollectionID: 1, ChannelName: "v4"}, Node: 2},
+				},
+			},
+			expectPlans:        []SegmentAssignPlan{},
+			expectChannelPlans: []ChannelAssignPlan{},
+		},
 		{
 			name:            "already balanced",
 			nodes:           []int64{11, 22},