Manual:DeleteArchivedRevisions.php

Deletes all the archived (hidden from public view) revisions, by clearing out the archive table. These revisions will no longer be restorable. The pages are permanently deleted.

When a page is 'deleted' by an administrator (Help:Sysop deleting and undeleting), records are moved from the 'revision' table to the 'archive' table, although the bulk of the data (page text) remains in the 'text' table. The script deletes all records from the archive table and then invokes purgeOldText.php to purge the text records which no revision links to. This can be useful for reducing the size of the database but it does mean you lose the ability to restore the according revisions.

Prior to MediaWiki 1.16, a helper file deleteArchivedRevisions.inc contained the class that performs the work. This class was merged into deleteArchivedRevisions.php in 1.16.