code: private void onRollBack(PersistenceDelegator delegator, Map<Object, EventLog> eventCol)
      {
          if (eventCol != null && !eventCol.isEmpty())
          {
              Collection<EventLog> events = eventCol.values();
              Iterator<EventLog> iter = events.iterator();
  
              while (iter.hasNext())
              {
                  try
                  {
                      EventLog event = iter.next();
                      Node node = event.getNode();
                      Class clazz = node.getDataClass();
                      EntityMetadata metadata = KunderaMetadataManager.getEntityMetadata(delegator.getKunderaMetadata(), clazz);
                      Client client = delegator.getClient(metadata);
  
                      // do manual rollback, if data is processed, and running
                      // without transaction or with kundera's default transaction
                      // support!
                      if (node.isProcessed()
                              && (!delegator.isTransactionInProgress() || MetadataUtils
                                      .defaultTransactionSupported(metadata.getPersistenceUnit(), delegator.getKunderaMetadata())))
                      {
                          if (node.getOriginalNode() == null)
                          {
                              Object entityId = node.getEntityId();
                              client.remove(node.getData(), entityId);
                          }
                          else
                          {
                              client.persist(node.getOriginalNode());
                          }
                      }
                      // mark it null for garbage collection.
                      event = null;
                  }
                  catch (Exception ex)
                  {
                      log.warn("Caught exception during rollback, Caused by:", ex);
                      // bypass to next event
                  }
              }
          }
          // mark it null for garbage collection.
          eventCol = null;
      }
docs: On roll back.
  
  @param delegator
  the delegator
  @param eventCol
  the event col