Comment by davidrowley

There is a pg_hint_plan extension. I think the danger with hints is that they might only be correct when written. If the table sizes or data skew changes, they might make things worse. I don't have a link to hand, but last time I recall a discussion on hints there was no general objection to them, providing the implementation could be done in a way that didn't force the planner's hand too strongly and still allowed it to adapt to the underlying data changing. For example, indicating there's a correlation between two columns, rather than specifying a given predicate matches 10 rows.