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=encoding utf8
=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
my $writer = MyDataWriter->new(
snapshot => $snapshot, # required
segment => $segment, # required
polyreader => $polyreader, # required
);
Abstract constructor.
=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_segment
$data_writer->add_segment(
reader => $reader # required
doc_map => $doc_map # default: undef
);
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
$data_writer->finish();
Complete the segment: close all streams, store metadata, etc.
=head2 format
my $int = $data_writer->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
$data_writer->delete_segment($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
$data_writer->merge_segment(
reader => $reader # required
doc_map => $doc_map # default: undef
);
Move content from an existing segment into the one currently being
written.
The default implementation calls L<add_segment()|/add_segment> then L<delete_segment()|/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
my $hashref = $data_writer->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
my $snapshot = $data_writer->get_snapshot();
Accessor for “snapshot” member var.
=head2 get_segment
my $segment = $data_writer->get_segment();
Accessor for “segment” member var.
=head2 get_polyreader
my $poly_reader = $data_writer->get_polyreader();
Accessor for “polyreader” member var.
=head2 get_schema
my $schema = $data_writer->get_schema();
Accessor for “schema” member var.
=head2 get_folder
my $folder = $data_writer->get_folder();
Accessor for “folder” member var.
=head1 INHERITANCE
Lucy::Index::DataWriter isa Clownfish::Obj.
=cut