fix: Set an empty segment if compaction deleted all inserts (#36044)

See also: #36038

---------

Signed-off-by: yangxuan <xuan.yang@zilliz.com>

internal/datanode/compaction/mix_compactor_test.go

@@ -270,7 +270,12 @@ func (s *MixCompactionTaskSuite) TestSplitMergeEntityExpired() {
 
 	compactionSegments, err := s.task.mergeSplit(s.task.ctx, [][]string{lo.Keys(kvs)}, nil)
 	s.NoError(err)
-	s.Equal(0, len(compactionSegments))
+	s.Equal(1, len(compactionSegments))
+	s.EqualValues(0, compactionSegments[0].GetNumOfRows())
+	s.EqualValues(19531, compactionSegments[0].GetSegmentID())
+	s.Empty(compactionSegments[0].GetDeltalogs())
+	s.Empty(compactionSegments[0].GetInsertLogs())
+	s.Empty(compactionSegments[0].GetField2StatslogPaths())
 }
 
 func (s *MixCompactionTaskSuite) TestMergeNoExpiration() {
@@ -280,10 +285,11 @@ func (s *MixCompactionTaskSuite) TestMergeNoExpiration() {
 		description string
 		deletions   map[interface{}]uint64
 		expectedRes int
+		leftNumRows int
 	}{
-		{"no deletion", nil, 1},
-		{"mismatch deletion", map[interface{}]uint64{int64(1): deleteTs}, 1},
-		{"deleted pk=4", map[interface{}]uint64{int64(4): deleteTs}, 0},
+		{"no deletion", nil, 1, 1},
+		{"mismatch deletion", map[interface{}]uint64{int64(1): deleteTs}, 1, 1},
+		{"deleted pk=4", map[interface{}]uint64{int64(4): deleteTs}, 1, 0},
 	}
 
 	alloc := allocator.NewLocalAllocator(888888, math.MaxInt64)
@@ -304,9 +310,7 @@ func (s *MixCompactionTaskSuite) TestMergeNoExpiration() {
 			res, err := s.task.mergeSplit(s.task.ctx, [][]string{lo.Keys(kvs)}, test.deletions)
 			s.NoError(err)
 			s.EqualValues(test.expectedRes, len(res))
-			if test.expectedRes > 0 {
-				s.EqualValues(1, res[0].GetNumOfRows())
-			}
+			s.EqualValues(test.leftNumRows, res[0].GetNumOfRows())
 		})
 	}
 }

internal/datanode/compaction/segment_writer.go

@@ -47,6 +47,7 @@ type MultiSegmentWriter struct {
 	// segID -> fieldID -> binlogs
 
 	res []*datapb.CompactionSegment
+	// DONOT leave it empty of all segments are deleted, just return a segment with zero meta for datacoord
 }
 
 type compactionAlloactor struct {
@@ -195,9 +196,27 @@ func (w *MultiSegmentWriter) Write(v *storage.Value) error {
 	return writer.Write(v)
 }
 
-// Could return an empty list if every insert of the segment is deleted
+func (w *MultiSegmentWriter) appendEmptySegment() error {
+	writer, err := w.getWriter()
+	if err != nil {
+		return err
+	}
+
+	w.res = append(w.res, &datapb.CompactionSegment{
+		SegmentID: writer.GetSegmentID(),
+		NumOfRows: 0,
+		Channel:   w.channel,
+	})
+	return nil
+}
+
+// DONOT return an empty list if every insert of the segment is deleted,
+// append an empty segment instead
 func (w *MultiSegmentWriter) Finish() ([]*datapb.CompactionSegment, error) {
 	if w.current == -1 {
+		if err := w.appendEmptySegment(); err != nil {
+			return nil, err
+		}
 		return w.res, nil
 	}