Saturday, November 8, 2008

Things That Make Us Go

I've just finished taking the (EM-based) Performance Tuning course and the SQL Tuning course. It's always a strange feeling taking a course where I already have hands-on experience, or I was around in the early days when standards were being hammered out.

Sometimes that odd feeling (I know this subject backwards and forwards, but I don't know THAT) is a disincentive to take a class. That's probably why I never took a C++ class, after doing the intro to the language with John Vlissides, hearing the early design discussions for the STL, and watching my department mate (and future manager) transcribe the original C++ reference manual to publish with IBM's first C++ compiler.

Other times, behind-the-scenes experience gives a dreamlike quality to the class. Small details become major epiphanies -- THAT'S what that person meant by that remark I didn't believe when they asked me to include it in the documentation. Discussions of timelines kick off a parallel track in my head -- yes, this feature first appeared in that release, but it almost made it in the previous release, or maybe it was there but never exposed, or it was almost called XYZ but changed at the last minute to ABC, and that's why the syntax is the way it is.

My mindset during the performance courses was a mixture of those feelings. I could handwave my way through 95% of the SQL stuff, but didn't know some of the reasons why technique X is just as fast as technique Y; or still believed urban myth Z, which stopped being true some time ago. (Like when SELECT DISTINCT stopped always returning results in sorted order.) I didn't know as much of the EM stuff, but it helped put into perspective why someone might need to know 50 pages worth of internal details just so they could decide whether or not to select one specific checkbox in some dialog.

Just to make things interesting, I took the Enterprise Manager course before the SQL course. The recommended order is the reverse. Sometimes, it's better to wade through the tough stuff first, being thrown into the deep end, and then feel like the easy stuff is a cinch. Like when I first read all those famous science fiction series, for one reason or another I usually read them out of order: Lord of the Rings (3, 1, 2), Dune (2, 3, 1), Riverworld (4, 1, then after that it's too complicated to explain).

My expectation with the SQL Tuning course, was that I would find out I had made dumb newbie decisions about bitmap indexes and function-based indexes all those years ago, and learn that index-organized tables were ideal for some new stuff I'm doing now. Actually, I learned that my original index choices were spot on, and my latest data structures might not be appropriate for IOTs after all.

I will revisit some of my ancient dealings with performance in light of the course material, and write some blog posts about what I find. Back in the late 8i days, I was in charge of the "Indexes" chapter in "Application Developer's Guide - Fundamentals". I was never satisfied with the presentation of bitmap, function-based, reverse key, etc. indexes, but I didn't know enough at the time to be dangerous.

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