[darksaints]

> Some RDBMS have mitigations, e.g. Oracle's optimizer plan stability allows you to make the plan unchangeable. It's a 2-sided knife of course: It won't get better if the data has a chance for it, but it won't get worse either.

That's simply not true, it's just less noticeable. Because even if your query plan is not changing, your data is. There will always be some point where your data grows and a reasonable planner (whether you or your database) has to adapt to that as it grows. For example, if a small lookup table grows enough, it stops being faster to do a full table scan on that table, and it becomes reasonable to do an index lookup. If your plan never changes, your performance gets worse. You may argue that fixed query plans are more predictable, but they are not objectively better.

[hyperman1]

To clarify: [the plan] won't get worse. It will of course be less adapted to the new reality. This generally means you'll get a gradual performance detoriation, but not an unexpected cliff. Gradual detoriation is preferrable on prod, as it gives you time to react without causing a major incident. Of course, if you ignore the warnings, you're just as dead.