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=head1 NAME

DBD::File::Roadmap - Planned Enhancements for DBD::File and pure Perl DBD's

Jens Rehsack - May 2010

=head1 SYNOPSIS

This document gives a high level overview of the future of the DBD::File DBI
driver and groundwork for pure Perl DBI drivers.

The planned enhancements cover features, testing, performance, reliability,
extensibility and more.

=head1 CHANGES AND ENHANCEMENTS

=head2 Features

There are some features missing we would like to add, but there is
no time plan:

=over 4

=item LOCK TABLE

The newly implemented internal common table meta storage area would allow
us to implement LOCK TABLE support based on file system C<flock ()>
support.

=item Transaction support

While DBD::AnyData recommends explicitly committing by importing and
exporting tables, DBD::File might be enhanced in a future version to allow
transparent transactions using the temporary tables of SQL::Statement as
shadow (dirty) tables.

Transaction support will heavily rely on lock table support.

=item Data Dictionary Persistence

SQL::Statement provides dictionary information when a "CREATE TABLE ..."
statement is executed. This dictionary is preserved for some statement
handle attribute fetches (as C<NULLABLE> or C<PRECISION>).

It is planned to extend DBD::File to support data dictionaries to work
on the tables in it. It is not planned to support one table in different
dictionaries, but you can have several dictionaries in one directory.

=item SQL Engine selecting on connect

Currently the SQL engine selected is chosen during the loading of the module
L<DBI::SQL::Nano>. Ideally end users should be able to select the engine
used in C<< DBI->connect () >> with a special DBD::File attribute.

=back

Other points of view to the planned features (and more features for the
SQL::Statement engine) are shown in L<SQL::Statement::Roadmap>.

=head2 Testing

DBD::File and the dependent DBD::DBM requires a lot more automated tests
covering API stability and compatibility with optional modules
like SQL::Statement.

=head2 Performance

Several arguments for support of features like indexes on columns
and cursors are made for DBD::CSV (which is a DBD::File based driver,
too).  Similar arguments could be made for DBD::DBM, DBD::AnyData,
DBD::RAM or DBD::PO etc.

To improve the performance of the underlying SQL engines, a clean
re-implementation seems to be required. Currently both engines are
prematurely optimized and therefore it is not trivial to provide
further optimization without the risk of breaking existing features.

Join the DBI developers IRC channel at L<irc://irc.perl.org/dbi> to
participate or post to the DBI Developers Mailing List.

=head2 Reliability

DBD::File currently lacks the following points:

=over 4

=item duplicate table names

It is currently possible to access a table quoted with a relative path
(a) and additionally using an absolute path (b). If (a) and (b) are
the same file that is not recognized (except for
flock protection handled by the Operating System) and two independent
tables are handled.