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=head1 NAME
Lucy::Index::DataWriter - Write data to an index.
=head1 SYNOPSIS
# Abstract base class.
=head1 DESCRIPTION
DataWriter is an abstract base class for writing index data, generally in
segment-sized chunks. Each component of an index -- e.g. stored fields,
lexicon, postings, deletions -- is represented by a
DataWriter/L<DataReader|Lucy::Index::DataReader> pair.
Components may be specified per index by subclassing
L<Architecture|Lucy::Plan::Architecture>.
=head1 CONSTRUCTORS
=head2 new( I<[labeled params]> )
my $writer = MyDataWriter->new(
snapshot => $snapshot, # required
segment => $segment, # required
polyreader => $polyreader, # required
);
=over
=item *
B<snapshot> - The Snapshot that will be committed at the end of the
indexing session.
=item *
B<segment> - The Segment in progress.
=item *
B<polyreader> - A PolyReader representing all existing data in the
index. (If the index is brand new, the PolyReader will have no
sub-readers).
=back
=head1 ABSTRACT METHODS
=head2 add_inverted_doc( I<[labeled params]> )
Process a document, previously inverted by C<< inverter >>.
=over
=item *
B<inverter> - An Inverter wrapping an inverted document.
=item *
B<doc_id> - Internal number assigned to this document within the
segment.
=back
=head2 add_segment( I<[labeled params]> )
Add content from an existing segment into the one currently being
written.
=over
=item *
B<reader> - The SegReader containing content to add.
=item *
B<doc_map> - An array of integers mapping old document ids to
new. Deleted documents are mapped to 0, indicating that they should be
skipped.
=back
=head2 finish()
Complete the segment: close all streams, store metadata, etc.
=head2 format()
Every writer must specify a file format revision number, which should
increment each time the format changes. Responsibility for revision
checking is left to the companion DataReader.
=head1 METHODS
=head2 delete_segment(reader)
Remove a segment's data. The default implementation is a no-op, as
all files within the segment directory will be automatically deleted.
Subclasses which manage their own files outside of the segment system
should override this method and use it as a trigger for cleaning up
obsolete data.
=over
=item *
B<reader> - The SegReader containing content to merge, which must
represent a segment which is part of the the current snapshot.
=back
=head2 merge_segment( I<[labeled params]> )
Move content from an existing segment into the one currently being
written.
The default implementation calls add_segment() then delete_segment().
=over
=item *
B<reader> - The SegReader containing content to merge, which must
represent a segment which is part of the the current snapshot.
=item *
B<doc_map> - An array of integers mapping old document ids to
new. Deleted documents are mapped to 0, indicating that they should be
skipped.
=back
=head2 metadata()
Arbitrary metadata to be serialized and stored by the Segment. The
default implementation supplies a Hash with a single key-value pair for
"format".
=head2 get_snapshot()
Accessor for "snapshot" member var.
=head2 get_segment()
Accessor for "segment" member var.
=head2 get_polyreader()
Accessor for "polyreader" member var.
=head2 get_schema()
Accessor for "schema" member var.
=head2 get_folder()
Accessor for "folder" member var.
=head1 INHERITANCE
Lucy::Index::DataWriter isa Clownfish::Obj.
=cut