Pressflow

We have mentioned before that both Pressflow 6.x and Drupal 7.x (but not core Drupal 6.x), disable page caching when a session is created for an anonymous user.

An extreme case of this happened recently, because of a perfect storm.

Symptoms

The client sends a newsletter to site users, be they who have accounts on the site, or others who just entered their email to get the newsletter.

Over the past few years, we were called in to assist clients with poor performance of their site. Many of these were using Pressflow, because it is "faster" and "more scalable" than Drupal 6.x.

However, some of these clients hurt their site's performance by using Pressflow, rather than plain Drupal, often because they misconfigured or misused it in some way or another.

Setting cache to "external" without having a caching reverse proxy