CUMULVS: Extending a Generic Steering and Visualization Middleware for Application Fault-Tolerance

CUMULVS is a middleware library that provides application programmers with a simple API for describing viewable and steerable elds in large-scale distributed simulations. These descriptions provide the data type, a logical name of the eld/parameter, and the mapping of global indices to local indices (processor and physical storage) for distributed data elds. The CUMULVS infrastructure uses these descriptions to allow an arbitrary number of front-end \viewer" programs to dynamically attach to a running simulation, select one or more elds for visualization, and update steerable variables. (Viewer programs can be built using commercial visualization software such as AVS or custom software based on GUI interface builders like Tcl/Tk.) Although these data eld descriptions require a small e ort on the part of the application programmer, the payo is a high degree of exibility for the infrastructure and end-user. This exibility has allowed us to extend the infrastructure to include \application-directed" checkpointing, where the application determines the essential state that must be saved for a restart. This has the advantage that checkpoints can be smaller and made portable across heterogeneous architectures using the semantic description information that can be included in the checkpoint le. Because many technical di culties, such as e cient I/O handling and time-coherency of data, are shared between visualization and checkpointing, it is advantageous to leverage a checkpoint/restart system against a visualization/steering infrastructure. Also, because CUResearch supported by the Applied Mathematical Sciences Research Program of the O ce of Energy Research, U.S. Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation 1060-3425/98 $10.0 MULVS \understands" parallel data distributions, efcient parallel checkpointing is achievable with a minimal amount of e ort on the programmer's part. However, application scientists must still determine what makes up the essential state needed for an application restart and provide the proper logic for restarting from a checkpoint versus normal startup. This paper will outline the structure and communication protocols used by CUMULVS for visualization and steering. We will develop the similarities and di erences between userdirected checkpointing and CUMULVS-based visualization. Finally, these concepts will be illustrated using a large synthetic seismic dataset code.