private static int compareQualifierPart(Cell cell, int length, byte[] prefix) {
    if (cell instanceof ByteBufferExtendedCell) {
      return ByteBufferUtils.compareTo(((ByteBufferExtendedCell) cell).getQualifierByteBuffer(),
        ((ByteBufferExtendedCell) cell).getQualifierPosition(), length, prefix, 0, length);
    }
    return Bytes.compareTo(cell.getQualifierArray(), cell.getQualifierOffset(), length, prefix, 0,
      length);
  }
This filter is used for selecting only those keys with columns that matches a particular prefix.
For example, if prefix is 'an', it will pass keys with columns like 'and', 'anti' but not keys
with columns like 'ball', 'act'.
hbase-client/src/main/java/org/apache/hadoop/hbase/filter/ColumnPrefixFilter.java