[stouset]

FK indexes by necessity need to be placed on the foreign table, which is just as likely to be a preexisting table that already contains data.

To be clear I 100% agree that adding indexes later is extremely painful. A little care when first creating tables goes a long way, and I’ve never seen a database fall over due to preemptive over-indexing but I’ve seen countless do so thanks to being underindexed.

Still, taking a DDL operation which is presumed to be essentially instantaneous and adding a default behavior that requires locking completely separate tables for a potentially-lengthy update does give me pause.