code: public void txnOfferBackupReserve(long itemId, String transactionId) {
          TxQueueItem o = txnOfferReserveInternal(itemId, transactionId);
          if (o != null) {
              logger.severe("txnOfferBackupReserve operation-> Item exists already at txMap for itemId: " + itemId);
          }
      }
docs: Reserves an ID for a future queue item and associates it with the given {@code transactionId}.
  The item is not yet visible in the queue, it is just reserved for future insertion.
  
  @param transactionId the ID of the transaction offering this item
  @param itemId        the ID of the item being reserved