> On Aug. 5, 2015, 5:46 a.m., Jie Yu wrote:
> > src/master/http.cpp, line 573
> > <https://reviews.apache.org/r/35702/diff/12/?file=1026443#file1026443line573>
> >
> >     What is 'Nothing' here?
> 
> Michael Park wrote:
>     The `Nothing` here comes from the result of `master->apply` which returns 
> a `Future<Nothing>`. But I feel like you're not actually asking for an answer 
> here?
>     
>     What would you like to see?
>     
>     What I have currently is a comment above the code which reads:
>     
>     ```cpp
>     // Propogate the 'Future<Nothing>' as 'Future<Response>' where
>     // 'Nothing' -> 'OK' and Failed -> 'Conflict'.
>     ```
> 
> Jie Yu wrote:
>     I mean if we remove 'Nothing' here, will it compile?

Oh, it does. I forgot about this behavior. Thanks, updated.


- Michael


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On Aug. 5, 2015, 7:12 p.m., Michael Park wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/35702/
> -----------------------------------------------------------
> 
> (Updated Aug. 5, 2015, 7:12 p.m.)
> 
> 
> Review request for mesos, Adam B, Benjamin Hindman, Ben Mahler, Jie Yu, Joris 
> Van Remoortere, and Vinod Kone.
> 
> 
> Bugs: MESOS-2600
>     https://issues.apache.org/jira/browse/MESOS-2600
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> This involved a lot more challenges than I anticipated, I've captured the 
> various approaches and limitations and deal-breakers of those approaches 
> here: [Master Endpoint Implementation 
> Challenges](https://docs.google.com/document/d/1cwVz4aKiCYP9Y4MOwHYZkyaiuEv7fArCye-vPvB2lAI/edit#)
> 
> Key points:
> 
> * This is a stop-gap solution until we shift the offer creation/management 
> logic from the master to the allocator.
> * `updateAvailable` and `updateSlave` are kept separate because
>   (1) `updateAvailable` is allowed to fail whereas `updateSlave` must not.
>   (2) `updateAvailable` returns a `Future` whereas `updateSlave` does not.
>   (3) `updateAvailable` never leaves the allocator in an over-allocated state 
> and must not, whereas `updateSlave` does, and can.
> * The algorithm:
>     * Initially, the master pessimistically assume that what seems like 
> "available" resources will be gone.
>       This is due to the race between the allocator scheduling an `allocate` 
> call to itself vs master's
>       `allocator->updateAvailable` invocation.
>       As such, we first try to satisfy the request only with the offered 
> resources.
>     * We greedily rescind one offer at a time until we've rescinded 
> sufficiently many offers.
>       IMPORTANT: We perform `recoverResources(..., Filters())` which has a 
> default `refuse_sec` of 5 seconds,
>       rather than `recoverResources(..., None())` so that we can virtually 
> always win the race against `allocate`.
>       In the rare case that we do lose, no disaster occurs. We simply fail to 
> satisfy the request.
>     * If we still don't have enough resources after resciding all offers, be 
> semi-optimistic and forward the
>       request to the allocator since there may be available resources to 
> satisfy the request.
>     * If the allocator returns a failure, report the error to the user with 
> `Conflict`.
> 
> This approach is clearly not ideal, since we would prefer to rescind as 
> little offers as possible.
> 
> 
> Diffs
> -----
> 
>   src/master/http.cpp 76e70801925041f08bc94f0ca18c86f1a573b2b3 
>   src/master/master.hpp e44174976aa64176916827bec4c911333c9a91db 
>   src/master/master.cpp 50b98248463fc4cd48962890c14c7ad64f2b6f43 
>   src/master/validation.hpp 43b8d84556e7f0a891dddf6185bbce7ca50b360a 
>   src/master/validation.cpp ffb7bf07b8a40d6e14f922eabcf46045462498b5 
> 
> Diff: https://reviews.apache.org/r/35702/diff/
> 
> 
> Testing
> -------
> 
> `make check`
> 
> 
> Thanks,
> 
> Michael Park
> 
>

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