[tornato7]

I worked at a company with a big, complex Postgres database behind the back end, probably half of all the incidents we had were related to the query planner suddenly deciding to change its approach.

Eventually you get a vague idea of how to coax Postgres to make the plans you want it to, but the fact that you can't at least lock it in and the plan might change with any number of factors at any time... That's just bad design.