Currently the Preference execution poliy is applied to each node individually and is identical to the OR execution policy. To sum up: despite its name, it has nothing to do with a "preference".

We propose to make it live up to its name, which implies:

• it should define a real order of preference for a number of node execution policies, where a node that satisfies policy N in the list will have priority over a node that satisfies policy N + 1
• it should be applied globally to all the nodes available to the driver
• because of the previous point, it should be a separate attribute of the job SLA
• it should be applicable to the client-side as well, where it would define a driver preference rather than a node preference
• special care should be taken about perfomance, as the algorithm will be in O(nbNodes * nbJobs). Should we allow parallel (with regards to the nodes) evaluation of the policy for each job?