ergophobe - 4:04 pm on Mar 18, 2008 (gmt 0)

There are a lot of things that affect this. Wordpress.com has over 100,000 new posts added every day [wordpress.com] running on WordpressMU which is basically a version of wordpress with a wrapper to manage it for multiple users.

Having thousands of articles is not really the issue. Searching through a giant text file will scale roughly linearly as size increases. Retrieving data via simple queries ("get me article 10523") from a database with searches on properly indexed columns, load will increase quite slowly as a function of the size of the data set. Complex queries are another matter, but most queries that WP issues are fairly straightforward.

It's having zillions of page requests and scads of plugins that are more likely to bog things down (some add significant load, some do not, but you can test that with XDebug and Cachegrind).

How well it scales for traffic is affected by things like

- hardware (obviously)

- plugins - do they add DB queries? Do they add css and js files that get downloaded separately (remember, only 1-2 streams at a time)?

- theme - how many different pieces does the theme need to serve up a page? (i.e. same considerations as a non-dynamic page)

- caching - at the WP level as well as PHP accelerators (ioncube and whatnot)

So I don't have any WP sites with lots of pages or lots of traffic, let alone both, but with other CMS I have seen how something that runs like lightning can be brought to a halt by a couple of really load-heavy modules or one bad PHP funciton, and my limited experience (emphasize that!) says that WP can be tuned for speed or tuned to lug.

Another question to ask yourself about scaling is how well does it scale to building many sites off one code base. There are options with WP, but say drupal (and joomla?) have that capability designed into the bones. If you have, just hypothetically, say several thousand domains that ended in "directory" and wanted to build some sort of directory site for each one, how easy would it be to manage it in WP? My gut reaction is that without building some custom scripts, it could be a hassle (I'm in the process of combining a handful of WP sites onto one codebase, which is easy, but getting settings to propagate automatically is harder - and yes, I know about WordpressMU but don't want to use it).