performance

The DevShed technical tour explains that MySQL can spawn new threads, each of which can execute on a different processor/core. What it doesn’t say is that a single thread can only execute on a single core, and if that thread locks a table, then no other threads that need that table can execute until the locking thread/query is complete. Short answer: MySQL works well on multi-core machines until you lock a table.

The good news is that performance is a big goal for WP 2.4, the bad news is that it’s been delayed to the end of January at the earliest.

It was part of a long thread among WordPress hackers over the summer and fall, but this post at VulgarisOverIP just reminded of it: minify promises to be an easy way to compress external CSS and JavaScript without adding extra steps to your develop/deploy process. No, really, look at the usage instructions. (To be clear, the Vulgaris and Google Code versions are different, one derived from the other and backported to PHP4 compatible. Still, the concept is the same.)

Vulgaris reports a nearly 300% decrease in time to download, definitely worth the effort.

Yes, I’m still trying to squeeze more performance out of MySQL. And since small changes to a query can make a big difference in performance…

Here are two really easy things to be aware of:

• Never do a COUNT(*) (or anything *, says Zach). Instead, replace the * with the name of the column you’re searching against (and is hopefully indexed). That way some queries can execute entirely in the keycache (while * forces MySQL to read every matching row from the table).
• When joining two large tables, but only searching against one, put the join statement at the end. Why join the two entire tables when you only have to join the matching rows?

I mention these because, well, I’ve known them forever, but upon seeing them again I realized I hadn’t really obeyed those simple rules in some of my queries.

Separately, there’s some pretty good info on what server variables affect what at mysqlperformanceblog too.

Harry Shearer and Judith Owen are performing their holiday sing-a-long at the concert hall at the Society for Ethical Culture in NYC with guests TMBG and others. It’s a go on Friday, but why can’t these things happen closer to me? Actually, maybe they should all come to Warren afterwards.