Section: User Contributed Perl Documentation (3pm)
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DBD::File::Roadmap - Planned Enhancements for DBD::File and pure Perl DBD's
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, reliability,
extensibility and more.
CHANGES AND ENHANCEMENTS
There are some features missing we would like to add, but there is
no time plan:
- LOCK TABLE
The newly implemented internal common table meta storage area would allow
us to implement LOCK TABLE support based on file system "flock ()"
- 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.
- 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
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 <irc://irc.perl.org/dbi> to
participate 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 protection 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 handling, ...)
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:
# 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 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)
RESOURCES AND CONTRIBUTIONS
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''
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.
- CHANGES AND ENHANCEMENTS
- RESOURCES AND CONTRIBUTIONS