I recently updated my blog theme to use P2. P2 is a free WordPress theme that gives your site more of a Tumblr / Twitter style look.
In general, I liked it. However, I noticed that the performance really sucked. Digging in deeper it turns out the culprit is the P2 variable “mentionData.” I presume it is used to allow the mention feature to work. What it does is preload all of the user profile data onto the page. This can be bad news for a WordPress instance with a lot of users.
I had over 700 users on the site (that was another problem that I rectified), on each page load it P2 will fill in the mentionData variable with all 700+ account holders.
I’ve since deleted the offending users and my performance is great again. I don’t know enough about the theme to want to dive in and take a look at it. Hopefully the guys at Automattic can fix this.