presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/index/Indexer.java/Indexer/getLocalityGroups
class Indexer:    public static Map<String, Set<Text>> getLocalityGroups(AccumuloTable table)
    {
        Map<String, Set<Text>> groups = new HashMap<>();
        // For each indexed column
        for (AccumuloColumnHandle columnHandle : table.getColumns().stream().filter(AccumuloColumnHandle::isIndexed).collect(Collectors.toList())) {
            // Create a Text version of the index column family
            Text indexColumnFamily = new Text(getIndexColumnFamily(columnHandle.getFamily().get().getBytes(UTF_8), columnHandle.getQualifier().get().getBytes(UTF_8)).array());

            // Add this to the locality groups,
            // it is a 1:1 mapping of locality group to column families
            groups.put(indexColumnFamily.toString(), ImmutableSet.of(indexColumnFamily));
        }
        return groups;
    }