Lucy::Index::Segment - Warehouse for information about one segment of an inverted index.


    # Index-time.
    package MyDataWriter;
    use base qw( Lucy::Index::DataWriter );

    sub finish {
        my $self     = shift;
        my $segment  = $self->get_segment;
        my $metadata = $self->SUPER::metadata();
        $metadata->{foo} = $self->get_foo;
            key       => 'my_component',
            metadata  => $metadata

    # Search-time.
    package MyDataReader;
    use base qw( Lucy::Index::DataReader );

    sub new {
        my $self     = shift->SUPER::new(@_);
        my $segment  = $self->get_segment;
        my $metadata = $segment->fetch_metadata('my_component');
        if ($metadata) {
            $self->set_foo( $metadata->{foo} );
        return $self;


Apache Lucy’s indexes are made up of individual “segments”, each of which is is an independent inverted index. On the file system, each segment is a directory within the main index directory whose name starts with “seg_”: “seg_2”, “seg_5a”, etc.

Each Segment object keeps track of information about an index segment: its fields, document count, and so on. The Segment object itself writes one file, segmeta.json; besides storing info needed by Segment itself, the “segmeta” file serves as a central repository for metadata generated by other index components – relieving them of the burden of storing metadata themselves.



    my $int = $segment->add_field($field);

Register a new field and assign it a field number. If the field was already known, nothing happens.

  • field - Field name.

Returns: the field’s field number, which is a positive integer.


        key      => $key,       # required
        metadata => $metadata,  # required

Store arbitrary information in the segment’s metadata hash, to be serialized later. Throws an error if key is used twice.

  • key - String identifying an index component.

  • metadata - JSON-izable data structure.


    my $obj = $segment->fetch_metadata($key);

Fetch a value from the Segment’s metadata hash.


    my $int = $segment->field_num($field);

Given a field name, return its field number for this segment (which may differ from its number in other segments). Return 0 (an invalid field number) if the field name can’t be found.

  • field - Field name.


    my $string = $segment->field_name($field_num);

Given a field number, return the name of its field, or undef if the field name can’t be found.


    my $string = $segment->get_name();

Getter for the object’s seg name.


    my $int = $segment->get_number();

Getter for the segment number.



Setter for the object’s document count.


    my $int = $segment->get_count();

Getter for the object’s document count.


    my $int = $segment->compare_to($other);

Compare by segment number.


Lucy::Index::Segment isa Clownfish::Obj.