Isolation Scheduler Hosts Sorting | Add secondary sort (No of free slots) and tertiary sort (Hostname)

[meetjain74]

What is the purpose of the change

All things are mentioned in the Issue #8708

How was the change tested

Deployed topologies after the changes and is working as expected.

[reiabreu]

Hi @meetjain74 ! What do you think about adding some unit tests for this? Thank you

[reiabreu]

can we iterate over hostAssignableSlots in the outer loop? This will reduce the number of iterations, since hostAssignableSlots contains the target hosts

[reiabreu]

ran this through an LLM.

Suggested approach to avoid doing Map lookup in every sort iteration

 1. Add freeSlots to HostAssignableSlots:

  1     class HostAssignableSlots {
  2         private final int freeSlots; 
  3         // ... update constructor and add getter
  4     }

  2. Calculate once per host, then sort:

   1     // Build objects with pre-calculated metadata
   2     for (Map.Entry<String, List<WorkerSlot>> entry : hostAssignableSlots.entrySet()) {
   3         int free = (int) entry.getValue().stream().filter(cluster::isSlotAvailable).count();
   4         sortHostAssignSlots.add(new HostAssignableSlots(entry.getKey(), entry.getValue(), free));
   5     }
   6
   7     // Faster Comparator (Direct field access)
   8     Collections.sort(sortHostAssignSlots, (o1, o2) -> {
   9         int bySlots = o2.getWorkerSlots().size() - o1.getWorkerSlots().size();
  10         if (bySlots != 0) return bySlots;
  11         
  12         int byFree = o2.getFreeSlots() - o1.getFreeSlots();
  13         if (byFree != 0) return byFree;
  14         
  15         return o1.getHostName().compareTo(o2.getHostName());
  16     });
`