code: private JSONArray retrievePerPartitionTransactionIds() {
          JSONArray retval = new JSONArray();
          try {
              ByteBuffer values = ByteBuffer.wrap(m_zk.getData(VoltZK.perPartitionTxnIds, false, null));
              int numKeys = values.getInt();
              for (int ii = 0; ii < numKeys; ii++) {
                  retval.put(values.getLong());
              }
          } catch (KeeperException.NoNodeException e) {/*doesn't have to exist*/}
          catch (Exception e) {
              VoltDB.crashLocalVoltDB("Failed to retrieve per partition transaction ids for snapshot", false, e);
          }
          return retval;
      }
docs: /*
  If this cluster has per partition transactions ids carried over from
  previous instances, retrieve them from ZK and pass them to snapshot save so that it can
  include them in the snapshot