Recently I’ve been taking daily backups of a 4.2GB mediawiki (v1.5.6) database, about 3.9GB of which was in the ‘text’ table. It was all the previous versions of pages that were taking up the space so having looked at http://meta.wikimedia.org/wiki/Help:Reduce_size_of_the_database I decided to give deleteOldRevisions.php a go.