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DBD::File::Roadmap(3) User Contributed Perl DocumentationDBD::File::Roadmap(3)

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

       Jens Rehsack - May 2010

       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, relia‐
       bility, extensibility and more.


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

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

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

	   Transaction support will heavily rely on lock table support.

       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 "NULLABLE" or "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.

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

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


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


       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 reim‐
       plementation seems to be required. Currently both engines are prema‐
       turely 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 <irc://irc.perl.org/dbi> to par‐
       ticipate or post to the DBI Developers Mailing List.


       DBD::File currently lacks the following points:

       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 pro‐
	   tection handled by the Operating System) and two independent tables
	   are handled.

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


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

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

	   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.

	   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

       Our priorities are focussed 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 (pay‐
       ing) users.

       See <http://dbi.perl.org/contributing> for 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
       <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

       Using such targeted financing allows you to contribute to DBI develop‐
       ment and rapidly get something specific and directly valuable to you in

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

       Thank you.

perl v5.8.8			  2010-07-02		 DBD::File::Roadmap(3)
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