There are already several ways to force postgres to use or not use a particular index. We use cloud-hosted and managed Postgres instances on one of the major provider, and I've used a couple of these strategies to massage the query planner.

1. Fiddle with the Query Planner settings (this can be done on a per query level as well, so its not global). E.g. enable_indexscan=off, enable_indexonlyscan=off

2. Add a trivial calculation to the filter clause of the query. E.g. select * from table where indexed_col + 0 = 12345 shouldn't use the index, as the planner won't do the arithmetic.

3. Use the pg_hintplan extension, which allows you to add comments to your code to urge the planner to use certain data access strategies, including specifying which indices to use. See: https://pg-hint-plan.readthedocs.io/en/latest/hint_table.htm...

That second trick is neat, I'll need to remember that. I also really wish I had known about it back in 2015, when we had to massage an inconveniently big (at the time) PG database and started to carve it out into smaller, purpose-specific instances.

Being able to verify that an index was either useless or inefficient without jumping through hoops would have saved quite a lot of time.