An Extended Two-Phase Method for Accessing Sections of Out-of-Core Arrays

A number of applications on parallel computers deal with very large data sets that cannot t in main memory In such applications data must be stored in les on disks and fetched into memory during program execution Parallel programs with large out of core arrays stored in les must read write smaller sections of the arrays from to les In this paper we describe a method for accessing sections of out of core arrays e ciently Our method the extended two phase method uses collective I O Processors cooperate to combine several I O requests into fewer larger granularity requests reorder requests so that the le is accessed in proper sequence and eliminate simultaneous I O requests for the same data In addition the I O workload is divided among processors dynamically depending on the access requests We present performance results obtained from two real out of core parallel applications matrix multiplication and a Laplace s equation solver and several synthetic access patterns all on the Intel Touchstone Delta These results indicate that the extended two phase method signi cantly outperformed a direct noncollective method for accessing out of core array sections This work was supported in part by the Scalable I O Initiative a multiagency project funded by the Advanced Research Projects Agency contract number DABT C the Department of Energy the National Aero nautics and Space Administration and the National Science Foundation by a National Science Foundation Young Investigator Award CCR and by a grant from Intel Scalable Systems Division This work was performed in part using the Intel Touchstone Delta System operated by Caltech on behalf of the Concurrent Supercomputing Consortium Access to this facility was provided by the Center for Research on Parallel Computation