When an update leaves things inconsistent.
WHAT HAPPENS
Many updates change the database structure as well as the code.
If the code updated and the database routine did not run, they are out of step.
THE SYMPTOM
Errors about missing columns or tables Features not working The application reporting a database update is required
THE FIX
Run the application's database update routine.
WordPress prompts for this on the admin screen after a core update.
Drupal has an update script that must be visited after any core or module update.
Others vary; check the documentation.
IF THE UPDATE FAILED PARTWAY
Restore your backup, which is why you took one before updating.
Then update again, having addressed whatever caused the failure: usually memory, execution time, or disk space.
IF YOU HAVE NO BACKUP
Re-run the update. Most applications handle being run again.
If the schema is genuinely inconsistent, that is difficult without a backup.
PREVENTION
Back up before every update Raise limits before large updates Run the database routine promptly after the code update
