To permit easy and efficient access to non-contiguous regions in memory for communication and I/O the message passing interface offers nested datatypes. Since nested datatypes can be very complicated, the understanding of non-contiguous access patterns and the debugging of wrongly accessed memory regions is hard for the developer. HDTrace is an environment which allows to trace the behavior of MPI programs and to simulate them for arbitrary
virtual cluster configuration. It is designed to record all MPI parameters including MPI datatypes. In this paper we present the capabilities to visualize usage of derived datatypes for communication and I/O accesses – a simple hierarchical view is introduced which presents them in a compact form and allows to dig into the nested datatypes. File regions accessed in non-contiguous I/O calls can be visualized in terms of the original datatype. The presented feature assists developers in understanding the datatype layout and spatial I/O access patterns of their application.

@inproceedings{VOMDKL12,
	author	 = {Julian Kunkel and Thomas Ludwig},
	title	 = {{Visualization of MPI(-IO) Datatypes}},
	year	 = {2012},
	booktitle	 = {{Applications, Tools and Techniques on the Road to Exascale Computing}},
	editor	 = {Koen De Bosschere and Erik H. D'Hollander and Gerhard R. Joubert and David Padua and Frans Peters},
	publisher	 = {IOS Press},
	address	 = {Amsterdam, Berlin, Tokyo, Washington DC},
	series	 = {Advances in Parallel Computing},
	number	 = {22},
	pages	 = {473--480},
	conference	 = {ParCo 2011},
	organization	 = {University of Ghent, ELIS Department},
	location	 = {Ghent, Belgium},
	isbn	 = {978-1-61499-040-6},
	issn	 = {0927-5452},
	abstract	 = {To permit easy and efficient access to non-contiguous regions in memory for communication and I/O the message passing interface offers nested datatypes. Since nested datatypes can be very complicated, the understanding of non-contiguous access patterns and the debugging of wrongly accessed memory regions is hard for the developer. HDTrace is an environment which allows to trace the behavior of MPI programs and to simulate them for arbitrary  virtual cluster configuration. It is designed to record all MPI parameters including MPI datatypes. In this paper we present the capabilities to visualize usage of derived datatypes for communication and I/O accesses -- a simple hierarchical view is introduced which presents them in a compact form and allows to dig into the nested datatypes. File regions accessed in non-contiguous I/O calls can be visualized in terms of the original datatype. The presented feature assists developers in understanding the datatype layout and spatial I/O access patterns of their application.},
}