saved by9 people, first bygozomama on 2007-04-10, last byMatt M on 2008-05-19
Justin Silverton at Jaslabs has a supposed list of 10 tips for optimizing MySQL queries. I couldn't read this and let it stand because this list is really, really bad. Some guy named Mike noted this, too. So in this entry I'll do two things: first, I'll explain why his list is bad; second, I'll present my own list which, hopefully, is much better. Onward, intrepid readers!
The rule in any situation where you want to opimize some code is that you first profile it and then find the bottlenecks. Mr. Silverton, however, aims right for the tippy top of the trees. I'd say 60% of database optimization is properly understanding SQL and the basics of databases. You need to understand joins vs. subselects, column indices, how to normalize data, etc. The next 35% is understanding the performance characteristics of your database of choice. COUNT(*) in MySQL, for example, can either be almost-free or painfully slow depending on which storage engine you're using. Other things to consider: under what conditions does your database invalidate caches, when does it sort on disk rather than in memory, when does it need to create temporary tables, etc. The final 5%, where few ever need venture, is where Mr. Silverton spends most of his time. Never once in my life have I used SQL_SMALL_RESULT.
