protected Pair<Long, Row> computeNext()
{
if (rows == null || !rows.hasNext())
return endOfData();
Row row = rows.next();
Map<String, ByteBuffer> keyColumns = new HashMap<String, ByteBuffer>();
for (String column : partitionBoundColumns.keySet())
keyColumns.put(column, row.getBytesUnsafe(column));
// increase total CF row read
if (previousRowKey.isEmpty() && !keyColumns.isEmpty())
{
previousRowKey = keyColumns;