NPAC Technical Report SCCS-685
Accessing Sections of Out-of-Core Arrays Using an Extended Two-Phase Method
Rajeev Thakur, Alok Choudhary
Submitted January 10 1995
Abstract
In out-of-core computations, data needs to be moved back and forth between
main memory and disks during program execution. In this paper, we
propose a technique called the Extended Two-Phase Method, for
accessing sections of out-of-core arrays efficiently. This
is an extension and generalization of the Two-Phase Method for reading
in-core arrays from files, which was previously proposed
in [Rosario93,Bordawekar93]. The Extended Two-Phase Method uses
collective I/O in which all processors cooperate to perform I/O
in an efficient manner by combining several I/O requests into fewer
larger requests, eliminating multiple disk accesses for the same data
and reducing contention for
disks. We describe the algorithms for reading as well
as writing array sections. Performance results on the Intel Touchstone
Delta for many different access patterns are presented and analyzed.
It is observed that the Extended Two-Phase Method gives consistently
good performance over a wide range of access patterns.