User:DWalden (WMF)/(Un)delete associated talk page

What happens when you delete a page edit

Before delete edit


After delete edit


  1. Rows in the revision table are copied into the archive table
  2. Rows in the revision, revision_actor_temp and revision_comment_temp tables are deleted
  3. Row in the page table is deleted
  4. Rows deleted from page_restrictions, redirect, *links, if they existed in the first place
  5. Row inserted into logging table which records the delete action
  6. If deleted page had rows in the recentchanges table (e.g. for edits), they are deleted
  7. Row inserted into recentchanges table which records the delete action

SQL queries edit

(see also API:Database_field_and_API_property_associations)

What happens when you delete a file edit

Files on MediaWiki also have a page associated with them (whose titles are prefixed with "File:" e.g. File:Page_UML_diagram.png). So, what is written above about pages also applies to files.

In addition, there are three database tables:

  • image, stores information about the most recent version of a file
  • oldimage, stores information about older versions of a file
  • filearchive, stores information on deleted files

When you delete edit

  1. Rows from image and oldimage are copied to the filearchive table
  2. Rows deleted from image and oldimage tables
  3. In the filestore, the current and old versions of the file are moved to the $wgDeletedDirectory

SQL queries edit

Where to find files edit

Test Ideas edit

ACID edit

What bugs can we find related to ACID properties (atomicity, consistency, isolation, durability)? (see also MIT's Computer System Engineering course week 8, week 9, week 10. Video lectures [1].)

Consistency edit

  • After deleting or restoring pages or files, does the data in the database end up in inconsistent states?
  • Do all the appropriate rows get deleted or restored?
  • Are all the appropriate relationships between data maintained?
  • For example, I attempted to delete this image via the UI. It timed out. The rows in the revision and page tables were deleted, but the rows in the image table were not. Notice, for example, that even though the page appears to exist, it has a link to "Create" it.
  • Perhaps use ideas from chapter 7 of Explore It!

Use cases edit

Factors edit

Permissions edit

  • Only users with the delete right (which usually is only users in the Administrator or sysop group) can delete a page/file.
  • Only users with the bigdelete right (usually those in the Stewards group) can delete a page/file with over 5000 revisions (or whatever the value of $wgDeleteRevisionsLimit).
  • Users can be blocked from some or all pages. For example, you can block a user from the Talk namespace, which would prevent them deleting a talk page.

"Big" pages edit

  • When deleting pages or files with over 1000 revisions (or whatever the value of $wgDeleteRevisionsBatchSize), instead of all the revisions being deleted in one go they are done in batches.
  • SQL query to list the top 10 pages with most revision: /big_page_sql.
  • To add a large number of edits/revisions to a page you can use /mass_edit.
  • You could combine this with #ACID test ideas above.

Redirects edit

  • Make sure that when we delete pages which are redirects, we delete the redirect itself and not the target of the redirect (see phab:T295435).
  • When you move a page over another page that already exists, the page is deleted to make way for the page you are moving. This is another way of deleting a page.

Tools edit

  • Adding a large number of revisions to a page or file /mass_edit.

Sessions edit