[development] Good article on MEMORY temp tables in MySQL

* This could be particularly relevant to Drupal.org if we are still *>* getting temp tables written to disk. It turns out that even when we *>* specify MEMORY for temp tables, MySQL still has the option of writing to *>* disk if other buffers aren't large enough.*

This problem has been driving me totally nuts for months now. Until I read this I've assumed that it was something that I was missing/doing wrong. Thanks for sharing the 411.