public int[] getKeyColumns() throws SQLException {
        throw new UnsupportedOperationException();
    }
Returns the columns that make a key to uniquely identify a
row in this <code>CachedRowSetImpl</code> object.

@return an array of column numbers that constitutes a primary
          key for this rowset. This array should be empty
          if no column is representitive of a primary key
@throws SQLException if the rowset is empty or no columns
          are designated as primary keys
@see #setKeyColumns
src/main/java/org/replicadb/rowset/sun/rowset/internal/SyncResolverImpl.java