=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.

=item invalid table names

The current implementation does not prevent someone choosing a
directory name as a physical file name for the table to open.

=back

=head2 Extensibility

I (Jens Rehsack) have some (partially for example only) DBD's in mind:

=over 4

=item DBD::Sys

Derive DBD::Sys from a common code base shared with DBD::File which handles
all the emulation DBI needs (as getinfo, SQL engine handling, ...)

=item DBD::Dir

Provide a DBD::File derived to work with fixed table definitions through the
file system to demonstrate how DBI / Pure Perl DBDs could handle databases
with hierarchical structures.

=item DBD::Join

Provide a DBI driver which is able to manage multiple connections to other
Databases (as DBD::Multiplex), but allow them to point to different data
sources and allow joins between the tables of them:

  # Example
  # Let table 'lsof' being a table in DBD::Sys giving a list of open files using lsof utility
  # Let table 'dir' being a atable from DBD::Dir
  $sth = $dbh->prepare( "select * from dir,lsof where path='/documents' and dir.entry = lsof.filename" )
  $sth->execute(); # gives all open files in '/documents'
  ...

  # Let table 'filesys' a DBD::Sys table of known file systems on current host
  # Let table 'applications' a table of your Configuration Management Database
  #  where current applications (relocatable, with mountpoints for filesystems)
  #  are stored
  $sth = dbh->prepare( "select * from applications,filesys where " .
                       "application.mountpoint = filesys.mountpoint and ".
		       "filesys.mounted is true" );
  $sth->execute(); # gives all currently mounted applications on this host

=back

=head1 PRIORITIES

Our priorities are focused on current issues. Initially many new test
cases for DBD::File and DBD::DBM should be added to the DBI test
suite. After that some additional documentation on how to use the
DBD::File API will be provided.

Any additional priorities will come later and can be modified by (paying)
users.

=head1 RESOURCES AND CONTRIBUTIONS

See F<CONTRIBUTING.md> for I<how you can help>.

If your company has benefited from DBI, please consider if
it could make a donation to The Perl Foundation "DBI Development"
fund at L<http://dbi.perl.org/donate> to secure future development.

Alternatively, if your company would benefit from a specific new
DBI feature, please consider sponsoring it's development through
the options listed in the section "Commercial Support from the Author"
on L<http://dbi.perl.org/support/>.

Using such targeted financing allows you to contribute to DBI
development and rapidly get something specific and directly valuable
to you in return.

My company also offers annual support contracts for the DBI, which
provide another way to support the DBI and get something specific
in return. Contact me for details.

Thank you.

=cut
