Thread:Project:Support desk/Gigabytes of data taken up by MySQL database for mediawiki installation/reply (7)

You can safely delete all rows from mdw_searchindex and rebuild the search index later once the problem has been solved.

As per the backup, read Manual:Backing up a wiki. You can export the XML contents of the wiki running dumpBackup.php, in which case you can filter namespaces to not export the user: or talk: namespaces. Then you can delete the database and start from scratch, and import the generated xml dump again, now without those namespaces.

As per the entire database backup, compressing the generated backup shouldn't be 81GB, I'm sure it could compress it to a 10%.