Help: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.
How to purge
Just by clicking a link
Some pages already have a link like "purge this page", for example Wikipedia:Templates for discussion = WP:TFD. Then just clicking it purges.
WP:TFD transcludes subpages like Wikipedia: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
Template:Distinguish2 A null edit purges the page if the target page can be edited:
- Click the "Edit" tab at the top of the page.
- Click "Save" at the bottom of the edit box without making any changes.
With a null edit, nothing is usually saved, and no edit is typically recorded. If you leave text in the edit summary, it will probably be discarded and result in a null edit. Adding new blank lines only to the end of the page is also usually a null edit. Trailing blank lines are largely 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.
forcerecursivelinkupdate
The behaviour of null edits changed around July 2013. Null edits previously added all pages which transcluded the page to be added to the job queue to be reparsed. Now a null edit will reparse the page edited just as it always has (and therefore fix category membership and such), but it will no longer queue every transcluding page for reparse too.
A new "forcerecursivelinkupdate" parameter was added to the API's action=purge to get the old behavior if necessary. So action=purge&forcerecursivelinkupdate=1 in the URL (see below) will get the old behaviour. Only use this responsibly.
These changes do not affect normal edits that change the content of a page.
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 ?action=purge at the end of the URL, if the URL does not contain ?, a question mark, or equivalently, any =, equals signs. Otherwise, append &action=purge.
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 "?1" to the end, then do a usual purge. If there is still a problem, ask for help at Wikipedia:Village pump (technical).