3,174 research outputs found
Design and Evaluation of a Collective IO Model for Loosely Coupled Petascale Programming
Loosely coupled programming is a powerful paradigm for rapidly creating
higher-level applications from scientific programs on petascale systems,
typically using scripting languages. This paradigm is a form of many-task
computing (MTC) which focuses on the passing of data between programs as
ordinary files rather than messages. While it has the significant benefits of
decoupling producer and consumer and allowing existing application programs to
be executed in parallel with no recoding, its typical implementation using
shared file systems places a high performance burden on the overall system and
on the user who will analyze and consume the downstream data. Previous efforts
have achieved great speedups with loosely coupled programs, but have done so
with careful manual tuning of all shared file system access. In this work, we
evaluate a prototype collective IO model for file-based MTC. The model enables
efficient and easy distribution of input data files to computing nodes and
gathering of output results from them. It eliminates the need for such manual
tuning and makes the programming of large-scale clusters using a loosely
coupled model easier. Our approach, inspired by in-memory approaches to
collective operations for parallel programming, builds on fast local file
systems to provide high-speed local file caches for parallel scripts, uses a
broadcast approach to handle distribution of common input data, and uses
efficient scatter/gather and caching techniques for input and output. We
describe the design of the prototype model, its implementation on the Blue
Gene/P supercomputer, and present preliminary measurements of its performance
on synthetic benchmarks and on a large-scale molecular dynamics application.Comment: IEEE Many-Task Computing on Grids and Supercomputers (MTAGS08) 200
Complete subgraphs in a multipartite graph
In 1975 Bollob\'as, Erd\H os, and Szemer\'edi asked the following question:
given positive integers with , what is the largest
minimum degree among all -partite graphs with parts of size
and which do not contain a copy of ? The case has
attracted a lot of attention and was fully resolved by Haxell and Szab\'{o},
and Szab\'{o} and Tardos in 2006. In this paper we investigate the case
of the problem, which has remained dormant for over forty years. We resolve the
problem exactly in the case when , and up to an additive
constant for many other cases, including when . Our
approach utilizes a connection to the related problem of determining the
maximum of the minimum degrees among the family of balanced -partite
-vertex graphs of chromatic number at most
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