What are the key differences with Pressflow?

Question

I am currently using Drupal 7. I heard Pressflow is another solution for high performance sites.

If you have experience with both systems, what is the benefit of migrating from Drupal 7 to PressFlow 7? What are the major differences between Drupal 7 and Pressflow 7?

Answer 1

The differences with standard Drupal 7 are scattered about the Pressflow wiki though not documented very well, perhaps because Pressflow 7 is relatively new. (There is a comparison chart that has not been updated for Pressflow 7.)

Although it is sometimes said that Pressflow is a drag-and-drop replacement for Drupal because you usually don't have to make many changes to your modules' configuration, to get the most out of it you'll want to set up Varnish, APC, Memcached, etc. This will probably be impossible to do on a shared host; you'll need some sort of dedicated server and SSH access to go this route, and it's unnecessary to do so unless you actually have a high performance site.

If, however, like me you just like trying out new things, you could sign up for a free account with Pantheon (disclaimer: I'm a member), and try out Drupal on their servers. Pressflow, Varnish, etc. all come pre-configured. Pantheon was founded by David Strauss, who also co-founded Four Kitchens, the company behind Pressflow.

Answer 2

I dug in to find all of the differences and looked them up on GitHub and this is what I found:

• Pressflow Smart Start will forward you to the install page if the database is set up in settings.php but the database is empty, disabled by default.
  • Files: includes/bootstrap.inc and sites/default/default.settings.php
  • Commits: https://github.com/pressflow/7/commit/fa91b2fc80741cb8c42c2db618f0ef0ad890f4cc
• Allow for environmental PRESSFLOW_SETTINGS to override settings.php; settings must be entered as a JSON array.
  • Files: includes/bootstrap.inc
  • Commits: https://github.com/pressflow/7/commit/673fb0bdab618f8989365012149c76b8397f95d6 (Pull request: https://github.com/pressflow/7/pull/7), and https://github.com/pressflow/7/commit/953e6608b34975eaa0c8abed8a90f80d22f1b967
• APC CSS and JS check; to prevent Drupal from constantly checking the file system for core-aggregated CSS and JS files, use APC as a key:value store instead. This is very helpful for networked file systems (and therefore very relevant to Pantheon, who happens to be the primary driver behind Pressflow since version 7).
  • Files: includes/common.inc (also see lines 3558 and 4949)
  • Commits: https://github.com/pressflow/7/commit/e2f9d2b10b4f0c5f61f120be145621913c6794a4 (Pull request: https://github.com/pressflow/7/pull/16/files, original pull request: https://github.com/pantheon-systems/drops-7/pull/4)
• Allow modules to act on the js_cache before writing to disk, add a new hook called hook_js_cache_alter, and, if you use the new hook, add a note to the aggregated JavaScript that it was built with PressFlow
  • Files: includes/common.inc and modules/system/system.api.php
  • Commits: https://github.com/pressflow/7/commit/53098cf059236110716ca97c18565a178c458b43
• Allow sub-second delays for lock_wait(). The calculation Drupal currently does will allow a value of 0 for the lock wait time, effectively skipping it. When PHP converts to an integer, a float will always round down. For example, as Drupal performs the operation: php -r "echo (int) 0.25 * 2;" would return 0. The Pressflow change corrects this, for example: php -r "echo (int) (0.25 * 2);" would return 5, allowing for sub-second delays to be used as an input to the function.
  • Files: includes/lock.inc
  • Commits: https://github.com/pressflow/7/commit/2cd4323946987608a660694df2c02f3cb4cce6c3

Here's a full diff as of October 2013: https://gist.github.com/alanthing/6064500