I wrote a simple script to display a random blog that changes every 10 seconds. It worked on my computer but wouldn't work on this site. I spent a lot of time trying to get it to work, and I just found out that using order by rand() in a MySQL query can be such a resouce hog that it doesn't work at all.

I don't know how the internals of MySQL work, but I think it creates a temporary table, and then sorts it randomly, which is a huge waste. When you have over a million rows, and all you want is one randomly chosen row, MySQL is doing millions of times more work than it needs to.

My workaround was to choose a random number, and then use a limit clause to start at that number, and only return 1 row.