Side Channel

Let's get this out of the way first: MySQL beats PostgreSQL for Drupal sites in terms of raw performance. See this benchmark

But the real question is the how and why, and also how to make sites even faster and more scalable?

I'm not going to address all the possible factors at play here, there are too many of them, so I'm just touching on a number of the whys:

• Drupal issues a ''lot'' of queries, to the tune of about 100+ queries, including duplicates, per page. Many of these are very simple, name, value lookups, especially checking the links for aliases (aka drupal_lookup_path). The sheer strength and speed of MySQL and it's query caching means it wins over PostgreSQL hands down.

• Drupal doesn't really do transactions, and uses lock/unlock tables to force consistency across concurrent requests. One "unlock" request forces a COMMIT sql for PostgreSQL. In default installations, this means an fsync() is issued, and fsync on the default installation of Linux's ext3 is rather conservative. Their (ext3, postgreSQL) priority of safety over performance hurts drupal a lot. (Hint: ''default'' settings. synchronous_commit = off helps)

Now, why would anyone want to use PostgreSQL for drupal? Well, because we '''can''', and because I'm a diehard PostgreSQL user, and we believe in safe data. And we have several custom applications built on top of and integrated with Drupal (and we really want Postgis). It is working within the constrain of "must use PostgreSQL" that we have started to be able to track down some performance bottlenecks and getting insights in making things faster, particularly via our own distribution of Drupal, pulut.