code: @Override
    public LogIterator getIterator(Zxid zxid) throws IOException {
      SimpleLogIterator iter = new SimpleLogIterator(this.logFile);
      while(iter.hasNext()) {
        Transaction txn = iter.next();
        if(txn.getZxid().compareTo(zxid) >= 0) {
          iter.backward();
          break;
        }
      }
      return iter;
    }
docs: Gets an iterator to read transactions from this log starting
  at the given zxid (including zxid).
  
  @param zxid the id of the transaction.
  @return an iterator to read the next transaction in logs.
  @throws IOException in case of IO failure