fix: return correct compaction plan count by datacoord (#29980)

issue: #29943

---------

Signed-off-by: sunby <sunbingyi1992@gmail.com>

internal/datacoord/server_test.go

@@ -2477,6 +2477,15 @@ func TestManualCompaction(t *testing.T) {
 			},
 		}
 
+		mockHandler := NewMockCompactionPlanContext(t)
+		mockHandler.EXPECT().getCompactionTasksBySignalID(mock.Anything).Return(
+			[]*compactionTask{
+				{
+					triggerInfo: &compactionSignal{id: 1},
+					state:       executing,
+				},
+			})
+		svr.compactionHandler = mockHandler
 		resp, err := svr.ManualCompaction(context.TODO(), &milvuspb.ManualCompactionRequest{
 			CollectionID: 1,
 			Timetravel:   1,

internal/datacoord/services.go

@@ -1078,8 +1078,16 @@ func (s *Server) ManualCompaction(ctx context.Context, req *milvuspb.ManualCompa
 		return resp, nil
 	}
 
+	plans := s.compactionHandler.getCompactionTasksBySignalID(id)
+	if len(plans) == 0 {
+		resp.CompactionID = -1
+		resp.CompactionPlanCount = 0
+	} else {
+		resp.CompactionID = id
+		resp.CompactionPlanCount = int32(len(plans))
+	}
+
 	log.Info("success to trigger manual compaction", zap.Int64("compactionID", id))
-	resp.CompactionID = id
 	return resp, nil
 }