add debugging

go/vt/vttablet/tabletmanager/rpc_replication.go

@@ -476,10 +476,10 @@ func (tm *TabletManager) InitReplica(ctx context.Context, parent *topodatapb.Tab
 //
 // It attemps to idempotently ensure the following guarantees upon returning
 // successfully:
-//   * No future writes will be accepted.
-//   * No writes are in-flight.
-//   * MySQL is in read-only mode.
-//   * Semi-sync settings are consistent with a REPLICA tablet.
+//   - No future writes will be accepted.
+//   - No writes are in-flight.
+//   - MySQL is in read-only mode.
+//   - Semi-sync settings are consistent with a REPLICA tablet.
 //
 // If necessary, it waits for all in-flight writes to complete or time out.
 //
@@ -705,6 +705,7 @@ func (tm *TabletManager) setReplicationSourceRepairReplication(ctx context.Conte
 
 	ctx, unlock, lockErr := tm.TopoServer.LockShard(ctx, parent.Tablet.GetKeyspace(), parent.Tablet.GetShard(), fmt.Sprintf("repairReplication to %v as parent)", topoproto.TabletAliasString(parentAlias)))
 	if lockErr != nil {
+		log.Warningf("slack: failed to lock the shard with the error: %v", lockErr)
 		return lockErr
 	}