Codegen at Runtime

~ chriseyre2000 ~ 1 Comment
Codegen is usually used at build time to produce source code for an application.
However I have recently found a use for it at runtime (although infrequently).

The application that I work on has an archive process that takes the older data away to a secondary database. Periodically a new archive database is created.

We used to use dynamic sql within a stored procedure to move the data from the live to the archive. Strings were constructed within a stored procedure and executed. This turned out to be too slow.

I replaced the dyamic sql with a set of stored procedures that were regenerated at archive creation time using XSLT. This is exactly the same technique as traditional code generation, but  has provided a massive speed increase (3X to 7X improvements have been seen).

TDD Pragmatic Approach

~ chriseyre2000 ~ 1 Comment
Test Driven Developement is a development pratice in which the test are written before the code. The Cycle goes:

  1. Write a test, ensure that it fails [RED]
  2. Make the smallest possible change to get the test to work [GREEN]
  3. Refactor. Simplify the code to eliminate duplication and keep the design clean [REFACTOR]
  4. Repeat

The biggest mistake that people make when trying to get into test driven developement is to try to write all of the tests up front. This process is all about small error free steps.
The trick is to keep the tests small and focused. Don’t try to test too much with one test. If they are too fragile then you will spend your entire time rewriting your tests. As I write the tests I oftern find myself with a substantial helper object that performs the common tasks for me. The tests end up as documentation for the system.

Another important thing to remember is that this cycle is the formal version akin to the full blown scientific method:

  1. State Hypothesis
  2. Design an experiment, then perform it
  3. Identify whether Hypothesis is true or false
  4. Repeat

In addition if you have a project covered with automated tests adding new ones becomes simpler. It is especially powerful if you need to maintain several branches of a given codebase. If the helper object can keep it’s interface untouched across the streams then the tests can stay largely untouched.

I have sucessfully used this when porting an application from one database to another, but the technique would work in the same mannerif you were to change langauages. The trick is to create an abstract interface to test against. You write helper objects that implement that interface against the old and new systems. You write the tests against the old system and then implement the new in order to get the tests to build.

Dia

~ chriseyre2000 ~ 1 Comment
Dia is an open source diagramming tool on the edge of becoming a mainstream utility.
It does most of what Visio does but has a superior price tag.
It still has it’s rough edges but it looks like a promising project.

Codegen and Generative Programming

~ chriseyre2000 ~ 1 Comment
Kathleen Dollard’s CodegendotNet seems to satisfy Generative Programming Generators definition. Generative programming was a book that aimed to set the stage for improvements in productivity. Kathleen Dollard has provided examples to demonstrate how this technology can work. The main problem is that her demo works too well and people are trying to use it as the code generation template.

Here is the overview of codegen as implemneted in an OO-language: here

Knoppix ready for the Desktop

~ chriseyre2000 ~ Leave a comment
I maintain a website that is used to rehome unwanted cats.
Normally I would have used windows:

  • Paintshop Pro
  • AceFTP
  • Firefox

in my course of updting pictures and text to the site.

Due to a recent hard drive failure I have yet to reinstall Paintshop pro and decided to give Knoppix a go.

The stack:

  • GIMP
  • FTP
  • Mozilla

was perfectly adequate for the job. It took a while to get used to using GIMP, but it is far more powerful than PSP 5 that I had been using.

I thought that I had a problem with accessing the photos from my camara until I found that the USB cable was not plugged into the PC.

I am amazed with how well Knoppix configures a basic PC.
It recognises and configures my soundcard automatically – something that Windows 2000 cannot do.

Performance of dynamic sql

~ chriseyre2000 ~ Leave a comment
You would expect that dynamic sql, that is a string constructed in a stored procedure and then executed would be slower than the equivalent as a stored procedure. However I was surprised to find that an application become 7 times faster by removing this.

The dynamic sql allowed the database to be accessed to be specific at call time. However at any given time only one other database was being used. By replacing the appropriate stored procedures at change over time we obtain a substantial performance benefit.