One of the DrupalCon presentations that I wanted to be sure to watch early on was Databases: The Next Generation, presented by database maintainer and self described gadfly Larry Garfield.
There have been some big changes in the Database Abstraction layer in Drupal 7, which I've been using in patches to core and porting a contib module or two to D7. I've already groked dynamic queries and why they are great from reading up on PDO, but since most of my database experience has been using Drupal 6, I still haven't quite figured out how transactions work even though they've been around in databases for a long time ....and I have no idea about how to make master/slave work.
Even though, as Garfield says, everything in this presentation is covered in the docs at http://drupal.org/node/310069, this presentation is a great and worthwhile intro to the D7 db abstraction layer.
@arianesays thanks! glad it was helpful (and sorry for delay). Slides are @ http://slidesha.re/cUWxR3 and video is @ http://bit.ly/bLDWPw
Shakesville: The Terrible Bargain We Have Regretfully Struck