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=head1 NAME

Lucy::Index::DeletionsWriter - Abstract base class for marking documents as deleted.

=head1 SYNOPSIS

    my $polyreader  = $del_writer->get_polyreader;
    my $seg_readers = $polyreader->seg_readers;
    for my $seg_reader (@$seg_readers) {
        my $count = $del_writer->seg_del_count( $seg_reader->get_seg_name );
        ...
    }



=head1 DESCRIPTION

Subclasses of DeletionsWriter provide a low-level mechanism for declaring a
document deleted from an index.

Because files in an index are never modified, and because it is not
practical to delete entire segments, a DeletionsWriter does not actually
remove documents from the index.  Instead, it communicates to a search-time
companion DeletionsReader which documents are deleted in such a way that it
can create a Matcher iterator.

Documents are truly deleted only when the segments which contain them are
merged into new ones.



=head1 ABSTRACT METHODS

=head2 delete_by_term( I<[labeled params]> )

Delete all documents in the index that index the supplied term.

=over

=item *

B<field> - The name of an indexed field. (If it is not spec'd as
C<< indexed >>, an error will occur.)

=item *

B<term> - The term which identifies docs to be marked as deleted.  If
C<< field >> is associated with an Analyzer, C<< term >>
will be processed automatically (so don't pre-process it yourself).

=back

=head2 delete_by_query(query)

Delete all documents in the index that match C<< query >>.

=over

=item *

B<query> - A L<Query|Lucy::Search::Query>.

=back

=head2 updated()

Returns true if there are updates that need to be written.

=head2 seg_del_count(seg_name)

Return the number of deletions for a given segment.

=over

=item *

B<seg_name> - The name of the segment.

=back





=head1 INHERITANCE

Lucy::Index::DeletionsWriter isa L<Lucy::Index::DataWriter> isa L<Lucy::Object::Obj>.


=cut