Upgrading WordPress – A Peack under the Hood

What happens when we click Upgrade Now?

  • WordPress creates automatically a file named .maintenance
  • All these files might be overriden:
    • All the files under /wp-includes/
    • All the files under /wp-admin/
    • Any wordpress’ original theme folder (Twentyten, Twentyeleven etc..) under wp_content/
    • All files directly under wordpress’ root
  • A couple of files/folders may be added to wp_content/
  • On the database, The “db_upgraded” flag on the wp_options table is set to “0”
  • If all went well, WordPress deletes automatically the .maintenance file

Once done, the right db and system versions are recorded on the wp_config.php file:
* The WordPress version string
* @global string $wp_version
$wp_version = '3.1.3';

* Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
* @global int $wp_db_version
$wp_db_version = 17516;

If anything goes wrong – here’s an interesting article with some suggestions for troubleshooting.