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Software Dissonance: Slow Migrations

This weekend one of my choral ensembles had a lesson in dissonance. The two bass parts hold a (dissonant) whole tone interval, which eventually resolves down to a (harmonious) minor third. We were having trouble getting the intonation right, so our choir director had us go very slowly and hold the dissonant interval so our ears would be accustomed to the sound.

Just like music, over time software systems cycle between dissonance and harmony. One significant way dissonance occurs is during migration. In a migration, multiple valid domain models partly overlap. The dissonance is created because they embody slightly different assumptions, structure and capability - yet they share elements in common. When the old model falls away, dissonance resolves to harmony, and the cycle renews.

Most software teams minimize the duration of their migrations, perhaps regarding them as unpleasant or untidy. In my current work setting, my team cannot risk an abrupt migration because there are too many moving parts and too low a tolerance for failure. Like my choir director did with the whole tone interval in the bass parts, my team draws out the migration to get the notes right.

Doing a prolonged migration like ours, we struggle to give clear names, to synchronize data and to guide our business processes. It must seem a cacophony of tumultuous change and instability! Analysts are learning the new system and unlearning the old, while both systems run together slightly out of step. Slowly the intonation stabilizes.

In one month from now we will be free of the old constructs, and we will reach a phase of comparative harmony. But for now we hold the dissonance as our ears adjust.

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