I'm curious what does
SELECT COUNT(DISTINCT old_text), COUNT(*) FROM text;
show on Wikipedia's database? On mine I get
COUNT(DISTINCT old_text): 2913
COUNT(*): 3560
I.e., 1/7 of the rows are redundant.
Currently undos, so frequent on wikis, just blindly create a duplicate row
instead of checking if the old one could be reused,
https://bugzilla.wikimedia.org/show_bug.cgi?id=18333 . Maybe some hardware
savings could even be achieved.