Is it slow now?
I don’t know anything about PostgreSQL’s performance characteristics. And ultimately you would have to benchmark the query on your configuration.
There may be cases where an active column can be the best solution but there is the trade off of the required additional update the needs to happen within the same transaction as the insert (both of which affect the index).
Another alternative is to formulate the query around due_for_return and put an index on that but I don’t think it’s going to perform any better than using the primary key index.
