CorporisPublica:Purge

The purge function is a handy way to make an incorrectly displaying CorporisPublica page display correctly by clearing the page’s server cache. This forces the wiki software to rebuild the page completely.

Some pages use transclusion to incorporate subpages or templates. If you can’t see the transcluded pages properly, purging might help. However purging does not apply new categorisation and "what links here" changes from templates; in these cases a null edit is required.

Anyone can request that a purge be performed, including anonymous editors. Issuing the command is not harmful to the operation of the website, but consumes a small amount of additional processing power to rebuild the page. You may want to try first to refresh the page using your web browser.

How to purge

 * Note: purging may take a few minutes, though it usually happens immediately.

There are four ways to purge the server cache:

The simplest way for editable pages:
 * Click the "Edit" tab at the top of the page.
 * Click "Save" at the bottom of the edit box without making any changes. This is a null edit. Nothing is saved. A null edit will not record an edit, nor make any entry in the page history or in Recent Changes, etc..

From any CorporisPublica page:
 * At the end of the URL in the address bar of your browser, add the text ?action=purge
 * Press or click "Go" to tell the browser to go to that revised URL
 * The page should be refreshed in a short time

Similarly, from any CorporisPublica page:
 * Click the "edit this page" tab (or "view source" tab if the page is protected)
 * In the address bar in your browser, at the end of the URL, where you see &action=edit, replace "edit" with "purge," so it now reads &action=purge
 * Press or click "Go" to tell the browser to go to that revised URL
 * The page should be refreshed in a short time

A fourth way is to use the purge template which creates a clickable link:
 * Go to the Sandbox (CorporisPublica:Sandbox)
 * Edit the page and add or
 * Save the page; this provides a permanent link on the page for purging. One may also just use preview, click on the link there to get to the purge page.
 * Click on the link it creates (you’ll see a blue link called "purge")

Purge gadgets
Logged-in users that have the Friendly clock enabled can purge the page by clicking the time at the top of the page. It acts as a purge link.

There is another gadget that adds a "*" tab to the top of the page. It purges the page’s server cache when clicked.

To enable the purge links go to "my preferences," and then to the gadgets tab. Search for "purge." Enable the clock gadget and/or the purge gadget. Both provide purge links at the top of the page. In Commons preferences there is a third gadget to add a toolbox link (sidebar usually) to generate new thumbnails. It shows up on image description pages on the Commons.

How it works
When a change is made to a page, the MediaWiki software saves the change to the main database. The next time a non-logged in user views the page, a copy of that page is made to a "server cache" on a set of secondary servers. Until the page is changed again, all non-logged in users who try to view that page will be shown the copy from the server cache. That way, users who are viewing but not editing do not put a drain on the main database server, and still see the most recent version of the page. (Logged-in users have a choice in their Special:Preferences under "Appearance" whether to see cached or live versions.)

Normally, when a change is made, the page is marked as "touched" and the software will create a new copy of the page for the server cache. However, when a change is made to a subpage or template, but not to the article page which transcludes it, the article page is not marked as "touched," and a new copy is not generated for the cache. Therefore anyone viewing the article page may see a cached page which includes old versions of the subpage or template.

The purge command forces the server cache to purge the old version of the page. The next time the page is viewed, the page will be rebuilt from scratch, including fresh versions of all subpages and templates, and a new copy will be made for the server cache. Note that this may take a few minutes in extreme cases.

For images
Purging an image’s description page can be used to force the software to regenerate all the thumbnails for that particular image. For images from the Commons purge the image description page on the Commons. The purge gadgets seem to work most consistently to force rescaling of all sizes of thumbnails of a particular image. See above:.

It may take a while for MediaWiki to get around to doing the rescaling, especially if it is an animated GIF. It depends on how busy the MediaWiki software is, and on the task queue. After a while reload the page that contains the thumbnail while bypassing your browser cache (Ctrl-F5 on Firefox). This may pull up the newly rescaled GIF thumbnail. See: CP:BYPASS. If this doesn’t work you may need to try later. You may need to purge that page with the thumbnails also. A simple page purge may work. If there is still a problem, ask for help at CorporisPublica:Village pump (technical).

If an image thumbnail will not regenerate successfully after the original image has been purged, 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. The thumbnail should then be successfully generated. Finally, do action=purge to delete the cached error. You should only do this if you have tried the above method and an action=purge, and neither have worked. When looking at an article page you may see old versions of thumbnailed images. There may be newer thumbnails, but they aren’t showing up on the article page. To force the newer thumbnails to show up, purge the article page. For editable pages the simplest way is do a null edit (see CP:Null edit). Click the edit link at the top of the page, and then save the page without making changes to the wikitext. Nothing is saved. A null edit will not record an edit, nor make any entry in the page history or in Recent Changes, etc.

=Resources=

Utilities

 * CorporisPublica:WikiProject User scripts/Scripts/Add purge to tabs – a user script which adds a purge tab to the row of tabs

Technical background

 * CorporisPublica:Transclusion
 * mw:Manual:Purge