TMSS-2886: little query optimization

SAS/TMSS/backend/src/tmss/tmssapp/views.py

@@ -757,10 +757,12 @@ def failure_report(request):
 def public_schedule(request):
     '''return the current and future running and scheduled units in either html table or json depending on the request accept header'''
     # get all current and future running and scheduled units
-    scheduled_or_running_units = models.SchedulingUnitBlueprint.objects.filter(status__value__in=models.SchedulingUnitStatus.ACTIVE_STATUS_VALUES) \
+    scheduled_or_running_units = models.SchedulingUnitBlueprint.objects.prefetch_related('task_blueprints__specifications_template__type') \
+                                                                       .select_related(models.SchedulingUnitBlueprint.path_to_project, 'status', 'specifications_template', 'specifications_template') \
+                                                                       .filter(status__value__in=models.SchedulingUnitStatus.ACTIVE_STATUS_VALUES) \
                                                                        .filter(obsolete_since__isnull=True) \
                                                                        .filter(on_sky_stop_time__gte=datetime.utcnow()) \
-                                                                       .order_by('on_sky_start_time').all()
+                                                                       .order_by('on_sky_start_time').all()[:3]
 
     # return json if requested
     if 'json' in request.headers.get('Accept','').lower():