SQL::Statement::RoadmaUser Contributed Perl DocumentSQL::Statement::Roadmap(3)NAMESQL::Statement::Roadmap - Planned Enhancements for SQL::Statement and
SQL::Parser
Jens Rehsack - June 2010
SYNOPSIS
This document gives a high level overview of the future of
SQL::Statement, SQL::Parser and its impact.
The planned enhancements cover testing, performance, reliability,
extensibility and more.
CHANGES AND ENHANCEMENTS
Enhancements in SQL::Statement 1.xx
SQL::Statement 1.xx will not receive big changes, but a few
enhancements may help us to design SQL::Statement 2.xx much better.
CREATE and DROP of FUNCTION, KEYWORD, OPERATOR, TYPE
SQL::Statement is missing some functions, types, operators etc. It's
supported to add missing functionality - but the implementation wasn't
picked up during the modernizing of column evaluation. See RT#52397 for
some more information.
This should be done before SQL::Statement 1.xx reaches the end of its
road.
Parser improvements
The SQL::Parser is implemented based on a lot of regular expressions
and some manually developed logic. This creates some issues like
RT#53416 or RT#55190. Further, trailing ";" causes SQL::Parser to
croak. We need to decide what can be fixed without internal design
changes and what has to wait.
Performance
There is no intention to work on performance improvements in
SQL::Statement 1.xx. The performance is good as it is and improvement
requires design changes.
Reliability
Bugs will be fixed - where possible. SQL::Statement 1.28 is much more
reliable than SQL::Statement 1.15. Even if a bug cannot be fixed all
issues are gratefully received as they will be considered in the design
process for SQL::Statement 2.xx better.
Extensibility
SQL::Statement 1.xx is highly extensible, even if a more object
oriented design would improve that. The 1.xx branch will not be
redesigned for greater extensibility on a coding level.
Enhancements in SQL::Statement 2.xx
Concerning the procedural design of SQL::Statement 1.xx a rewrite of
the basic components is required.
SQL::Parser rewrite
The SQL::Parser needs to be modified to be able to use a
http://en.wikipedia.org/wiki/Backus_Naur_Form. This would allow users
and developers to rely on many different SQL dialects. This will allow
better extensibility from a feature point of view without losing ANSI
SQL compatibility.
SQL::Statement rewrite
SQL::Statement should be reduced to a simple coordinating engine. The
executing tasks should be organized into separated commands. This will
reduce side effects and will open the door for higher level
optimizations, reliability improvements or sub-selects (or other
calculated tables).
Features
There is a large list of missing features but not all table backends
will be able to support each new feature. The most popular requested
features need additional discussion and everyone is welcome to do it on
the mailto:dbi-dev@perl.org.
LOCK TABLE
Locking table within SQL scripts to manually control table consistence
over several operations. The current locking support is restricted to
one statement.
Transaction support
Executing statements on a temporary copy of the table data.
The easiest way to implement this would be to create a
SQL::Statement::RAM on "BEGIN TRANSACTION" and write the entire table
back on "COMMIT" or discard on "ROLLBACK".
Better performance could be acheived when the implementation allows to
memorize the single modification and apply them at "COMMIT". This needs
more discussion.
ALTER TABLE
Adding, removing or modifying columns is not supported for created
tables. A generic "ALTER TABLE" seems to rely on the implementation of
the transaction support - until better ideas are provided.
Indices
Currently some table backends have implicit support to access specified
rows quicker than fetching each row and evaluating the where clause
against the row data.
An interface would be required to configure fetching to return only
rows matching a restricted where clause. Another (probably better) way
to support indices would be to fetch index entries at first and have an
interface to the table fetching lines based on an index key.
Sub-Selects
In most cases queries can be re-expressed without using sub-selects.
But in any case, there are circumstances where sub-selects are
required.
The first implementation will do the sub-select before the primary
statement is executed without any further optimization. Hopefully a
later version will provide better Performance with some optimization.
Query based variables
Currently the only variable I can imagine is "ROWNUM". More suggestions
are very welcome.
Better SQL Script support
In SQL::Statement 1.xx the function "RUN ()" provides SQL script
execution. This function may have limitations and side effects (at
least when the executed SQL touched the same tables as the primary
statement).
I plan to improve the SQL script support to remove the side effects on
the one hand and have a more flexible and easier way to execute them.
Finally it should be possible to execute a script via:
$dbh->do( join( ";", @script ) );
Trigger support
Most important when doing complicated things is having callback
functions for several events. While real triggers will not be possible
for SQL::Statement and underlying pseudo-databases, callbacks could be
provided via triggers.
Performance
There are several performance optimizations required for SQL::Statement
2.xx.
The first one should be done on a very high level (query optimization)
by implementing algebraic evaluation of queries and clean
implementation of typical database algorithms. With respect to the
basic optimization rule premature optimization is the root of all evil,
it is primarily targeted to have an adequately fast, reliable
implementation of many algorithms (e.g. early incomplete evaluation to
reduce amount of rows, transpose where clause to evaluate constants
first) and a clever controller choosing the right algorithm for a
specific query.
The second optimization goal means: implementing most expensive methods
in XS. This requires a good performance test suite as well as some real
world useage cases.
Reliability
This is one of the primary goals of SQL::Statement. I hope to reach it
using test driven development and I hope I get some more todo's from
the users for this.
Extensibility
The currently high level of extensibility should be increased on a
coding level. This will be done by redesigning the entire parser and
execution engine using object oriented techniques and design patterns.
Testing
Many tests in SQL::Statement are not well organized. The tests should
be reorganized into several parts:
Basic API
This part should test the entire basic API of SQL::Statement,
SQL::Parser and probably the entire engine command classes.
DBI / Table API
This part should test if the API to DBI drivers work (maybe an
empty test driver will be needed for that).
Functionality
This part should test the functionality of the SQL::Parser and the
SQL::Statement engine.
Performance
This part should be used to implement full useage cases (ideally
from real world projects) to allow for testing optimizations.
PRIORITIES
Our priorities are localized to our current issues and proof of concept
fixes for upcoming SQL::Statement 2.xx.
Any additional priorities (as missing features, the SQL::Statement
rewrite) will come later and can be modified by (paying) users.
RESOURCES AND CONTRIBUTIONS
See <http://dbi.perl.org/contributing> for how you can help.
If your company has benefited from the DBI or SQL::Statement, please
consider if it could make a donation to The Perl Foundation "DBI
Development" or "SQL::Statement Development" fund at
<http://dbi.perl.org/donate> to secure future development.
Alternatively, if your company would benefit from a specific new DBI or
SQL::Statement feature, please consider sponsoring its development
through the options listed in the section "Commercial Support from the
Author" on <http://dbi.perl.org/support/>.
Using such targeted financing allows you to contribute to DBI
development (including SQL::Statement and PurePerl DBI drivers) and
rapidly get something specific and directly valuable to you in return.
Thank you.
perl v5.14.1 2010-07-12 SQL::Statement::Roadmap(3)
