Martin Widlake's Yet Another Oracle Blog

Friday Philosophy – It’s not “Why Won’t It Work!” it’s “What Don’t I Understand?” April 27, 2012

I had a tricky performance problem to solve this week. Some SQL was running too slow to support the business need. I made the changes and additions I could see were needed to solve the problem and got the code running much faster – but it would not run faster consistently. It would run like a dream, then run slow, then run like a dream again 2 or 3 times and then run like a wounded donkey 3 or 4 times. It was very frustrating.

For many this would provoke the cry of “Why won’t it work!!!”. But I didn’t, I was crying “What don’t I understand???”. {I think I even did a bit of fist-pounding, but only quietly as my boss was sitting on the desk opposite me.}

I think I’ve always been a bit like that in respect of How Things Work”, but it has been enhanced within me by being blessed to work with or meet people for whom it is more important for them to understand why something is not working than fixing it.

I was reminded of this by a thoughtful comment in an email that one of the oaktable sent to the list. They made the comment that what they felt was common between members of the oaktable is “that we’re not interested (really) in what the solution is of most of our problems, but actually, what is the underlying issue that really causes the problem?”

It struck a real chord with me. Quite a few people I’ve come across seem to be fixated on wanting to know solutions – so that they can look knowledgeable and be “one of the best”. But that’s just stamp collecting really. It’s like one of those ‘games card’ fads that each generation of children has, where you want to collect the best cards so you can win. I never got it as a kid as there are few rules, tactics, ‘how it works’ to elucidate. What success is there in winning when it’s just down to the cards you have? {And being candid, I didn’t like them as partly as I never had the money to buy many cards and partly I was rubbish at trading them. No sales skills.}

I know the solve-it-don’t-just-fix-it position is a topic I have touched on before, but I think the attitude of trying to fix problems by understanding how it works is far more satisfying than doing so by knowing a set of solutions. You develop a deeper understanding to help solve new problems than any amount of solution-stamp-collecting ever will. However, another wise voice on the Oaktable discussion pointed out that you can be in a work environment where there is no time to investigate and you simply have to try your set of fixes and move on if you hit one that works. Your work environment can strongly influence how you work and, it some ways, the ways you think.

I bet some people are wondering what my problem at the start of this post actually was? Well, a nice technical blog about it may appear over the weekend, but the core reason for the toggling of working/not-working was partition swap. We have data coming into the system very fast. We build a new summary of the key data in one table and then swap it into active play via partition swap. On the live system, stats had not been gathered on the “swap” table we had introduced but had on the active table. So, each time the partition swapped, we went from good stats to “empty” stats or the other way around. The empty stats gave a quite, quite dreadful execution plan.