Saturday, August 23, 2008

Why Trigger

A few benefits of triggers in the mortgage commissions system

* testability -- To test the triggers, just run one or a bunch of inserts. Use sqsh, aqua studio, fitnesse or any other tool. If the logic is in Perl/Java, i don't think it would be so simple.
* Modular -- All (and only) the logic related to inserting records are contained in the triggers. This is separate from other logic. Separation of concern. Other developers are shielded from the complexity of saving records.

* complexity -- The insert trigger in the MtgAccts table involves more than 5 queries. To implement the same logic using Java or Perl would take 3-5 times more lines of code, by my estimate.

* flexibility -- during production support. Suppose we need to load a few records for a production issue. Just write the query by hand and test in QA and then run it in sqsh/aqua or another tool.
* reuse -- 70% of the trigger code in MtgAccts table are used in other tables and also used in the spApproveMtg stored proc.

There are some concerns ...

* performance -- is not a top priority. Each month's load job takes less than 30 seconds now.
* UDB -- There's some concern over migrating stored proc and triggers to UDB. Trigger support in UDB is probably richer than sybase. Therefore the triggers are probably UDB-friendly.

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