fix: [2.4] Get all children deltalogs for segment to load (#40964)

issue: https://github.com/milvus-io/milvus/issues/40207
master pr: https://github.com/milvus-io/milvus/pull/40956
2.5 pr: #40957

Signed-off-by: Cai Zhang <cai.zhang@zilliz.com>

internal/datacoord/services.go

@@ -395,16 +395,38 @@ func (s *Server) GetSegmentInfo(ctx context.Context, req *datapb.GetSegmentInfoR
 	}
 	infos := make([]*datapb.SegmentInfo, 0, len(req.GetSegmentIDs()))
 	channelCPs := make(map[string]*msgpb.MsgPosition)
+
+	var getChildrenDelta func(id UniqueID) ([]*datapb.FieldBinlog, error)
+	getChildrenDelta = func(id UniqueID) ([]*datapb.FieldBinlog, error) {
+		children, ok := s.meta.GetCompactionTo(id)
+		// double-check the segment, maybe the segment is being dropped concurrently.
+		if !ok {
+			log.Warn("failed to get segment, this may have been cleaned", zap.Int64("segmentID", id))
+			err := merr.WrapErrSegmentNotFound(id)
+			return nil, err
+		}
+		allDeltaLogs := make([]*datapb.FieldBinlog, 0)
+		for _, child := range children {
+			clonedChild := child.Clone()
+			// child segment should decompress binlog path
+			binlog.DecompressBinLog(storage.DeleteBinlog, clonedChild.GetCollectionID(), clonedChild.GetPartitionID(), clonedChild.GetID(), clonedChild.GetDeltalogs())
+			allDeltaLogs = append(allDeltaLogs, clonedChild.GetDeltalogs()...)
+			allChildrenDeltas, err := getChildrenDelta(child.GetID())
+			if err != nil {
+				return nil, err
+			}
+			allDeltaLogs = append(allDeltaLogs, allChildrenDeltas...)
+		}
+
+		return allDeltaLogs, nil
+	}
+
 	for _, id := range req.SegmentIDs {
 		var info *SegmentInfo
 		if req.IncludeUnHealthy {
 			info = s.meta.GetSegment(id)
-			// TODO: GetCompactionTo should be removed and add into GetSegment method and protected by lock.
-			// Too much modification need to be applied to SegmentInfo, a refactor is needed.
-			children, ok := s.meta.GetCompactionTo(id)
-
 			// info may be not-nil, but ok is false when the segment is being dropped concurrently.
-			if info == nil || !ok {
+			if info == nil {
 				log.Warn("failed to get segment, this may have been cleaned", zap.Int64("segmentID", id))
 				err := merr.WrapErrSegmentNotFound(id)
 				resp.Status = merr.Status(err)
@@ -412,13 +434,14 @@ func (s *Server) GetSegmentInfo(ctx context.Context, req *datapb.GetSegmentInfoR
 			}
 
 			clonedInfo := info.Clone()
-			for _, child := range children {
+			// We should retrieve the deltalog of all child segments,
-				clonedChild := child.Clone()
+			// but due to the compaction constraint based on indexed segment, there will be at most two generations.
-				// child segment should decompress binlog path
+			allChildrenDeltalogs, err := getChildrenDelta(id)
-				binlog.DecompressBinLog(storage.DeleteBinlog, clonedChild.GetCollectionID(), clonedChild.GetPartitionID(), clonedChild.GetID(), clonedChild.GetDeltalogs())
+			if err != nil {
-				clonedInfo.Deltalogs = append(clonedInfo.Deltalogs, clonedChild.GetDeltalogs()...)
+				resp.Status = merr.Status(err)
-				clonedInfo.DmlPosition = clonedChild.GetDmlPosition()
+				return resp, nil
 			}
+			clonedInfo.Deltalogs = append(clonedInfo.Deltalogs, allChildrenDeltalogs...)
 			segmentutil.ReCalcRowCount(info.SegmentInfo, clonedInfo.SegmentInfo)
 			infos = append(infos, clonedInfo.SegmentInfo)
 		} else {