Collecting Trace Data

Prism creates one trace collection data file per process in your Sun MPI program. Sun HPC 3.0 ClusterTools supports Sun MPI programs with as many as 1024 processes on LSF, or as many as 256 processes on the Cluster Runtime Environment (CRE).

You can specify the size of the trace data collection files with the size argument of the tnffile command. The trace data collection files are allocated a fixed size, not a variable size limit. For example, to increase the size from the default value of 128 Kbytes to two megabytes,

(prism all) tnffile myfile.tnf 2048

Trace data collection files operate as circular buffers. As the file fills up with trace data records, older records are overwritten. Once the data collection process has been completed and the data has been merged in the final trace file, Prism will issue a warning message reporting that older records in the trace buffer have been overwritten, if that is the case. For example:

Maximum file size reached - some
events have been lost. 

It is difficult to predict the precise number of records that will fit in a given buffer size. Some probes report extra data--probe records vary in length. However, the average event generates a record roughly 16 bytes in length.

Tips for Controlling the Scale of Data Collection

• Change (lessen) the number of probes that you enable.

• Change (shorten) the duration of the time during which collection is active.