Use index order to prune sort size

As Sitaram Vemulapalli proposed, if the index provides a partial sort, we can use the index order to prune the sort size.

CREATE INDEX ON docs(a);

SELECT *

FROM docs

ORDER BY a, b

LIMIT 100;

The index does not fully sort the result. But after 100 records and a subsequent change in the value of a, we can abort the index scan and eliminate the remaining records.