All the tables that are innodb type (contenttype, searchcore, searchlog, searchgroup, tag, tagcontent) are showing insane overheads, hundreds of megabytes. Trying to repair them gives this message:
Note: Table does not support optimize, doing recreate + analyze instead
I went into phpmyadmin, changed these tables back to MyIsam, ran the repair, changed them back to innodb.
Result: contenttype+searchcore tables now show zero overhead. The rest of the tables show again hundreds of megabytes overhead. Each refresh I do, the overhead is changed! Every time the overhead becomes a bit lower, until after a while it goes back to hundreds of megabytes!!