[davidrowley]

Yeah, this is similar to some semi-baked ideas I was talking about in https://www.postgresql.org/message-id/CAApHDvo2sMPF9m=i+YPPU...

I think it should always be clear which open would scale better for additional rows over what the estimated row count is. We should always know this because we already cost for N rows, so it's possible to cost for N+1 rows and use the additional costs to calculate how the plan choice will scale when faced with more rows than expected.