Comment 27 for bug 919801

This tweak speeds up things a little for me, thanks!
You can automate it by creating a cron-job, e.g. create a file in /etc/cron.daily/, name it "cleanupdash" or whatever you want and paste

#!/bin/sh
sqlite3 ~/.local/share/zeitgeist/activity.sqlite vacuum

into it. Save it, change permission

sudo chmod 744 /etc/cron.daily/cleanupdash

and it will auto-execute itself once every day.
Enjoy!