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SQL::Statement::Roadmap(3pm) User Contributed Perl Documentation SQL::Statement::Roadmap(3pm)
NAME
SQL::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 was not 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 Backus Naur Form
<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 AT 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 achieved in cases where the implementation is enabled to
memorize pending modifications and apply them at "COMMIT". On the other hand there are
already capabilities to improve some operations, which might create confusion in case of
transactions.
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 usage 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 usage 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.
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