Controlling Buffer Size

When collecting TNF data, Prism creates a trace file for every process. Using the optional size argument, You can specify the maximum size (in kilobytes) of the output trace files used by each process. The default size is 128Kbytes. The output trace files are limited in size--once a file has been filled, more recent trace events overwrite the oldest ones. The following tnffile command example requests a trace file of 8192 Kbytes (8 Mbytes):

(prism all) tnffile myfile.tnf 8192

Since the TNF trace data buffer is limited in size, beware of allowing the trace data from the probes you are interested in to be overwritten by trace data from subsequent probes. For example, data from interesting events may be lost if those events occurred just prior to an area of your code that generates a lot of probe data. To reduce the chance that your probe data buffers are overwhelmed by especially busy sections of your code, use the tnfcollection command as an event action specifier (as described in "Collecting Performance Data") to focus attention on the most interesting routines.

You can also set the optional tnffile size argument to as large a value as your /usr/tmp allows. By enlarging the size of the trace data buffers with this command, you can reduce some of the probability that interesting data will get overwritten.