@AlexT: All scripts take as much of CPU as they need to run; whole the point is to make them light enough to not cause an issue. If it takes up to 0.5 seconds per request, it's obviously far too heavy for a recurring context like this, and won't scale up in a multi-user environment. 10 users means the query is made 2x per second, and that alone takes up the full CPU time. What if you have 50 users?

If you read through the files associated with action, it's obvious that there's a huge amount of see more optimization that can be done. For example:

- Add in an internal session cache to remember the results of the getBlockedUsers() and getUserInfo() queries -- two SQL queries off.
- Remove delete query, get new messages narrowed by time last queried, and have a cron job do the cleanup at set intervals.
- Go over the required files in XML.php, collect the necessary functions into a subset of files, and then make the calls through your "light" version -- without huge unnecessary overhead.