Fix not fill timestamp when use collection created ts (#22629)

Signed-off-by: Nyah01 <yang.cen@zilliz.com>

internal/datacoord/handler.go

@@ -280,7 +280,11 @@ func (h *ServerHandler) GetChannelSeekPosition(channel *channel, partitionID Uni
 }
 
 func getCollectionStartPosition(channel string, collectionInfo *collectionInfo) *msgpb.MsgPosition {
-	return toMsgPosition(channel, collectionInfo.StartPositions)
+	position := toMsgPosition(channel, collectionInfo.StartPositions)
+	if position != nil {
+		position.Timestamp = collectionInfo.CreatedAt
+	}
+	return position
 }
 
 func toMsgPosition(channel string, startPositions []*commonpb.KeyDataPair) *msgpb.MsgPosition {

internal/datacoord/meta.go

@@ -76,6 +76,7 @@ type collectionInfo struct {
 	Partitions     []int64
 	StartPositions []*commonpb.KeyDataPair
 	Properties     map[string]string
+	CreatedAt      Timestamp
 }
 
 // NewMeta creates meta from provided `kv.TxnKV`

internal/datacoord/server.go

@@ -1007,6 +1007,7 @@ func (s *Server) loadCollectionFromRootCoord(ctx context.Context, collectionID i
 		Partitions:     presp.PartitionIDs,
 		StartPositions: resp.GetStartPositions(),
 		Properties:     properties,
+		CreatedAt:      resp.GetCreatedTimestamp(),
 	}
 	s.meta.AddCollection(collInfo)
 	return nil