Controls if the query planner will produce a plan which will provide <literal>GROUP BY</literal> keys presorted in the order of keys of a child node of the plan, such as an index scan. When disabled, the query planner will produce a plan with <literal>GROUP BY</literal> keys only reordered to match
the <literal>ORDER BY</literal> clause, if any. When enabled, the planner will try to produce a more efficient plan. The default value is on.
A correction of myself: presorted -> sorted, reordered ->sorted
