You can use top jobs and starving jobs with fairshare. They just don’t play very well together.
The situation you can get into is where you have a top job. You one of the most deserving entities. We add your top job to the calendar and estimate where and when it will run. We won’t use those resources for other jobs. What can happen is your other running jobs are still accumulating usage. If your usage grows high enough, you are no longer one of the most deserving entities. Your job loses its top job slot. Once the usage balances out again, your job will need to wait for those resources all over again.
Now we do our best to avoid this situation. When a top job is added to the calendar, we temporarily add the job’s requested resources to its fairshare usage. This will lower the entity’s priority during that cycle. Now that the entity has a lower priority, their jobs are less likely to run. Less likely doesn’t mean the situation is completely avoided.
From your use cases above, it does sound that top jobs and fairshare are what you want. Just keep in mind that this unfortunate situation can occur.
Bhroam