If a job requires more units of a resource than are currently available, the server does not reserve the resource units by default. You can override this default and have the server reserve resources units when the required units are unavailable.
If a job does not reserve resources, a job requiring a lower resource count will receive the available resources first. As a result, jobs that require a large resource count may encounter processing delays, keeping the overall availability resource count low.
If a job reserves resources, the server reserves the resource units that are available at the time the job is next in the queue and holds them while waiting to accumulate the remainder of resource units required for that job.
Note: Only renewable and depletable resources can be reserved.
Example: Resource reservations
Suppose that job A requires 3 units of a resource and job B requires 2 units. Only 2 units of the resource are available and job A precedes job B in the queue.
If job A reserves resources, job A obtains the 2 units of the resource and waits for the third unit. Job B must wait for the 2 units to become available. Job A obtains the resource units before job B, even though job B required fewer resource units.
If job A does not reserve resources, job A must wait for 3 units to become available. Since job B only requires 2 units of the resource and 2 units of the resource are available, job B obtains the resource units first.
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