In an effort to reduce our traffic by cutting out unintentional reloads (particularly through using the 'back' and 'forward' buttons in Internet Explorer), certain accesses to Wikipedia are now marked to allow browsers to cache them.

Now cacheable are: - Viewing an article's current version - Viewing an older version of an article - Showing an article's history - Recent changes list

The browser still must check with the server to see if the page has changed, but if it hasn't the browser's cached version can be shown, saving a lot of database sorting, wikitext parsing, link checking, and bandwidth. If it has changed, you get the new version.

I haven't been able to get Mozilla to consistently behave correctly (probs with the expiry time; it doesn't check for updates), so for Gecko-based browsers the pages will still be marked as un-cacheable. This isn't as big a deal anyway, as Mozilla will in any case use cached pages when traversing the "back" and "forward" buttons; IE's forced reloads in this situation are the primary target.

(The pages are also marked 'private', so shared proxy caches shouldn't send one person's logged-in pages to another person.)

If anyone has (new) problems with pages showing old versions when they shouldn't, please let me know!

So far this is installed only on www.wikipedia.org and test.wikipedia.org. It'll go on meta and the rest of the languages soon when I get other things updated this weekend.

-- brion vibber (brion @ pobox.com)