On: Why PostgreSQL doesn't have query hints

[brlewis]

This snippet from the article makes me think their proposal only affects one query at a time:

For example, one which allowed you to put "SELECTIVITY 0.1" after a WHERE clause

[btilly → brlewis]

Oops, you're right.

Let me see. I can peer inside of a running black box and twiddle knobs that do something I don't understand until I magically get the right result. Then I can cross my fingers and hope it doesn't change out from under me.

Why does this not sound appealing?