Benefits and Drawbacks of Redundant Batch Requests |
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Authors: | Henri Casanova |
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Affiliation: | (1) Department of Information and Computer Sciences, University of Hawai‘i at Manoa, 1680 East–West Rd., Post 317, Honolulu, HI 96822, USA |
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Abstract: | Most parallel computing platforms are controlled by batch schedulers that place requests for computation in a queue until
access to compute nodes is granted. Queue waiting times are notoriously hard to predict, making it difficult for users not
only to estimate when their applications may start, but also to pick among multiple batch-scheduled platforms the one that
will produce the shortest turnaround time. As a result, an increasing number of users resort to “redundant requests”: several
requests are simultaneously submitted to multiple batch schedulers on behalf of a single job; once one of these requests is
granted access to compute nodes, the others are canceled. Using simulation as well as experiments with a production batch
scheduler we evaluate the impact of redundant requests on (1) average job performance, (2) schedule fairness, (3) system load,
and (4) system predictability. We find that some of the popularly held beliefs about the harmfulness of redundant batch requests
are unfounded. We also find that the two most critical issues with redundant requests are the additional load on current middleware
infrastructures and unfairness towards users who do not use redundant requests. Using our experimental results we quantify
both impacts in terms of the number of users who use redundant requests and of the amount of request redundancy these users
employ.
This work was supported by the NSF under Award 0546688. |
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Keywords: | job scheduling batch scheduling redundant requests |
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