1. A system, comprising: one or more processors; and logic encoded in one or more tangible media for execution by the one or more processors and when executed operable to perform operations comprising: assigning a virtual operating system container, operating on a single global kernel, from any of a reserve zone pool and a non-reserve zone pool to a task group, the task group comprising a set of tasks for a phase of a request, the phase comprising any of map or reduce; executing the set of tasks within the assigned virtual operating system container; and comparing an actual concurrency rate for each of a plurality of task groups to their expected concurrency rate, the comparing comprising determining a concurrency delta for each of the task groups of the plurality of task groups; and further comprising prioritizing the assignment of virtual operating system containers to the task groups based upon their concurrency deltas, and the task group of the plurality of task groups with a largest concurrency delta being assigned a virtual operating system container first.