B.1.5.RS:5.1 - Faster ordering in two encompassing uses

A team proposes replacing a stable sorting Method with a faster one that need not preserve the input order of equal keys.

One whole prepares a table showing how many records occur at each key. Internal order among equal keys does not affect those counts. Subject to the remaining input and performance conditions, the candidate can supply that contribution.

Another whole schedules requests by priority while retaining arrival order among requests of equal priority. Its method first orders records by arrival and then stably orders them by priority. Replacing the second sort with the candidate can reverse equal-priority requests. The earlier arrival ordering no longer survives the composition.

An allowed reversal of two equal-priority records with different arrival times exposes the incompatibility with the required guarantee. This is a counterexample to unrestricted replacement, not a prediction that this implementation reverses every such pair; repeated random benchmarks cannot restore the missing guarantee. Options include retaining the stable Method or sorting by an explicit compound key of priority and arrival. The compound-key candidate has changed the operation; compare its behavior and cost before using it. The same “sorted by priority” description concealed different requirements of the two wholes.