import org.apache.cassandra.io.util.MappedFileDataInput; //导入依赖的package包/类
/**
 * @return The segment containing the given position: must be closed after use.
 */
public FileDataInput getSegment(long position) {
    Segment segment = floor(position);
    if (segment.right != null) {
        // segment is mmap'd
        return new MappedFileDataInput(segment.right, path, segment.left, (int) (position - segment.left));
    }

    // not mmap'd: open a braf covering the segment
    // FIXME: brafs are unbounded, so this segment will cover the rest of the file, rather than just the row
    RandomAccessReader file = RandomAccessReader.open(new Path(path), fs);
    file.seek(position);
    return file;
}