I’ve got a lot of feedback on my last blogpost; one question was posted on another paltform where I’ve reblogged the same text, and this question was so interesting that I’ve decided to write a separate post in reply.
So tell me, Hettie, are these kind of discoveries being reported at the conferences, and would they later become a part of a common knowledgebase? Will this sort of technique be taught in colleges? Overall, in your opinion, are the nowadays CS graduates more knowledgeable in this area. And, by the way, is there any special knowledge which is necessary to be able to resolve problems like this, or it’s just a combination of basic knowledge plus experience?
Great question! I have being teaching optimization for almost 15 years, and in general my optimism on this subject is very modest. You can teach technique, you can show tons of examples, and still there is no guarantee that a student who has attended your class will be able to correctly identify a similar pattern in the real life and to recall what specific technique which was advised for a similar problem. But may be I am just not good in teaching this stuff.
It’s tempting to say, that all that matters are years of practice, but this is also not always the case, since you, and me, and all of us can recall the situations in which years of experience did not help. And to be honest, I do not want to wait for “years of experience”! I want to be able to hire a new grad, who can optimize at a reasonable level. And I am not saying I never met this kind of CS grads, but what I am saying is that whenever it happens, it is due to the person’s individual abilities and/or a desire to excel in this particular skill.
Let’s be clear: the kind of breakthrough as I’ve described in the previous post does not happen often. In fact, you might never get anything like this in your live. But there are still tons of optimizations which can be done almost every day.
I would still argue that knowing the basics is a key. For the thousandth time over – you need to know your math, your calc and your algebra in order to understand how databases work. You might not be aware of some sophisticated indexes, but you should be able to identify, looking at the query, what’s it about< whether it is "short" or "long". And if you try and try, and it does not become faster, you need all your convincing powers to convince yourself, that this query can be optimized. There should be a way.
Another big thing I am trying to teach – to write queries declaratively. This is an extremely challenging task, because most of the requirements are formulated in an imperative manner. So what I am trying to teach, is that even if you find something like “previous three occurrences”, or “return to the previous status”, or “compare the top two” in the requirements, you still can write a declarative statement, carefully using CASE, GROUP BY and sometimes window functions. And it’s amazing, how fast everything starts running right away. Most of the time being able to reduce the number of table scans to one does the trick, except of… well, except of the situation, when you should do exactly the opposite.
I didn’t figure out yet, how to teach to distinguish one from another :). But the more I think about it, there more it seems like that’s what signifies that somebody can optimize, and that skill is the most difficult to teach. Most optimization classes teach you how and when to use some indexes, and how to choose the join order, but they do not teach how to rewrite a query itself.
… For the original question: no, I do not think they teach it in school. But I am trying to promote this idea!