Saturday, June 10, 2006

Vlad points out my oversimplification

"Does everyone really say that performance tuning should be saved for last? "

Well ok, I meant deferred as long as possible, not dead last. People advocating this strategy include: Kent Beck, Martin Fowler, and I believe Ward Cunningham.

Martin Fowlers discussion
http://www.artima.com/intv/tunable.html

Kent Becks discussion
http://www.rolemodelsoftware.com/moreAboutUs/publications/articles/lazyopt.php

My experience:

On my last application we spent the majority of our time implementing the system and deferring performance. It took three developers six months to build. It was 10x too slow. It took 1 developer 3 weeks to rip out the guts of well factored code and put it back together fast enough.

Near the dawn of time, when I worked at OTI, there was a huge panic after IBM built Visual Age on top of OTI/Smalltalk because it was *WAY* too slow for them. One (Senior) developer, Steve, with the right tools(profiler and an open mind) went and assessed the situation. In a few hours things were all tickety boo. It was simply the way they were initializing their objects.

In my experience, with the code teams I've worked with, deferring performance saved time and money. It's the old 80/20 rule (80% of the time is spent in 20% of the code). In my experience, I think this is way closer to a 95/5 rule.

If you change (refactor) your code alot, that 5% will change alot too (it will be the heart of your system). How easy would allocation be to change if it had to meet performance criteria as well? How could we experiment?

1 Comments:

Blogger Vladimir Levin said...

Vald? :) I read and enjoyed the articles. They were both really good. I still have a bad feeling about leaving performance considerations until late in a project though. Let's say I put 100 identical looking vials in front of you and offer you $100,000 to drink one. Here's the deal: 99 vials have just plain water. 1 of the vials has a poison that leads to a slow and painful death. Would you do it? Chances are you would get the money, but would you really risk your life, even with a 99% probability in your favour? Say there's a 99% chance that performance problems can be dealt with effectively late in a project, but there is 1% chance that performance problems can't be dealt with effectively. Is it worth risking an entire project on faith that one will find ways to fix the problems?

12:01 p.m.  

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