code: public synchronized void truncate(long len) throws SQLException {
  
          try {
              blob.truncate(session, len);
          } catch (HsqlException e) {
              throw Util.sqlException(e);
          }
      }
docs: Truncates the <code>BLOB</code> value that this <code>Blob</code>
  object represents to be <code>len</code> bytes in length.
  
  @param len the length, in bytes, to which the <code>BLOB</code> value
  that this <code>Blob</code> object represents should be truncated
  @throws SQLException if there is an error accessing the
  <code>BLOB</code> value