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From "Meng Zhu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MESOS-8339) Quota headroom may be insufficiently held when role has more reservation than quota.
Date Fri, 15 Dec 2017 23:48:00 GMT
Meng Zhu created MESOS-8339:
-------------------------------

             Summary: Quota headroom may be insufficiently held when role has more reservation
than quota.
                 Key: MESOS-8339
                 URL: https://issues.apache.org/jira/browse/MESOS-8339
             Project: Mesos
          Issue Type: Bug
          Components: allocation
            Reporter: Meng Zhu


If a role has more reservation than its quota, the current quota headroom calculation is insufficient
in guaranteeing quota allocation.

Consider, role `A` with 100 (units of resource, same below) reservation and 10 quota and role
`B` with no reservation and 90 quota. Let's say there is no allocation yet. The existing allocator
would calculate that the required headroom is 100. And since unallocated quota role reserved
resource is also 100, no additional resources would be held back for the headroom.

While role `A` would have no problem getting its quota satisfied. Role `B` may have difficulty
getting any resources because the "headroom" can only be allocated to `A`.

The solution is to calculate per-role headroom before aggregating the quantity. And unallocated
reservations should not count towards quota headroom. In the above case. The headroom for
role `A` should be zero, the headroom for role `B` should be 90. Thus the aggregated headroom
will be `90`.



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