This is a fascinating study of the problems people get into when using ORMs to handle persistence concerns in their web applications. The authors study real-world applications and distil a catalogue of common performance anti-patterns. There are a bunch of familiar things in the list, and a few that surprised me with the amount of difference they can make. By fixing many of the issues that they find, Yang et al., are able to quantify how many lines of code it takes to address the issue, and what performance improvement the fix delivers.
Much of this is straightforward, but worth the read.