TechInfoDepot:Purge

Purge is sometimes necessary to update a wiki page, when templates or subpages transclusion is involved. Purge clears the page's server cache, and the page is rebuilt. Before purging, you may want to try first to refresh the page using your web browser.

For updating a page display, any purge methods do the job, but for categories and backlinks a null edit explained below is required, and other methods don't work. Update of images is explained in a section below.

The page to purge is the one that transcludes, not the page that gets transcluded. Purge consumes a small amount of additional processing power to rebuild the page.

Just by clicking a link
Some pages already have a link like "purge this page", for example TechInfoDepot:Templates for discussion = WP:TFD. Then just clicking it purges.

WP:TFD transcludes subpages like TechInfoDepot:Templates for discussion/Log/2012 December 17, and updates of these subpages are not always reflected in WP:TFD. By purging, you will see the latest.

Internally this technique is realized by purge request to server below. A purge link can be made by the purge template.

Null edit
A null edit purges the page if the target page can be edited:
 * 1) Click the "Edit" tab at the top of the page.
 * 2) Click "Save" at the bottom of the edit box without making any changes.

With a null edit, nothing is saved, and no edit is recorded. Even if you leave text in the edit summary, it will be discarded and result in a null edit. Adding newlines only to the end of the page is also a null edit. They are ignored. Section edits, however, sometimes result in changes, and get saved.

Page protection and move purges, too.


 * Advantage
 * All other purge methods do not apply to categorisation and "what links here" changes from template edits, but a null edit does.


 * Disadvantage
 * If you can't edit the page, you can't do a null edit, obviously. If what you want is category or backlink updates but you can't null-edit, just wait. It depends on how busy the server is until the page is updated, sometimes days. Changes in category links are put into the job queue, and re-cached when the server load is low.

Do not confuse null edit with dummy edit. A dummy edit does modify the source, even though slightly.

User preference
Logged-in users have some options in your Special:Preferences to help purging and bypassing browser caches. See also Special:Gadgets. For purge gadgets in Commons, see commons:Help:purge.

Purge request to server


You can also request the MediaWiki server to purge. Add  at the end of the URL, if the URL does not contain , a question mark, or equivalently, any  , equals signs. Otherwise, append.

It may be easiest to get this done by clicking "edit" or "view source" tab of the page, and change the last portion of the URL, "action=edit" to "action=purge".

Theory
When a change is made to a page, the MediaWiki software saves the change to the main database. Thereafter a copy of that page is made to a "server cache" on secondary servers, and until the page is changed again, that cached page will be shown. A change in a subpage or template does not necessarily generate a new cache of the transcluder page for efficiency. A purge throws away the cache, and rebuilds the page again.

For images
To refresh thumbnails, you may have to purge either or both of the image page and/or the page that loads the image. First go to the image description page by clicking the image. You should go further to Commons if the image is from Commons. Then purge. (Purge gadgets seem to work consistently. See commons:Help:Purge for Commons gadgets.) It may take a while for MediaWiki to complete rescaling, especially for an animated GIF. It depends on how busy the MediaWiki software is.

After a while, go back to the page with thumbnails and reload, bypassing your browser cache (Ctrl-F5 on Firefox). If the page still shows the old thumbnails, then purge this page.

If an image thumbnail will not yet regenerate successfully, it is probably because the server has cached an error page with the URL of a thumbnail, but the page is not purged because the actual thumbnail does not exist. The solution is to request the thumbnail with an unusual URL, say by appending " " to the end, then do a usual purge. If there is still a problem, ask for help at TechInfoDepot:Village pump (technical).

Technical background

 * TechInfoDepot:Transclusion
 * mw:Manual:Purge, mw:Manual:Cache, mw:Manual:Job queue