Execution, trace, and analysis Intervals

Edit online

In some cases, you can use the trace tool to capture the entire execution of a workload, while in other cases you will capture only an interval of the execution.

The execution interval is the entire time that a workload runs. This interval is arbitrarily long for server workloads that run continuously. The trace interval is the time actually captured in the trace log file by trace. The length of this trace interval is limited by how large a trace log file will fit on the file system.

In contrast, the analysis interval is the portion of the trace interval that is analyzed by the splat command. The -t and -T flags indicate to the splat command to start and finish analysis some number of seconds after the first event in the trace. By default, the splat command analyzes the entire trace, so this analysis interval is the same as the trace interval.

Note: As an optimization, the splat command stops reading the trace when it finishes its analysis, so it indicates that the trace and analysis intervals end at the same time even if they do not.

To most accurately estimate the effect of lock activity on the computation, you will usually want to capture the longest trace interval that you can, and analyze that entire interval with the splat command. The -t and -T flags are usually used for debugging purposes to study the behavior of the splat command across a few events in the trace.

As a rule, either use large buffers when collecting a trace, or limit the captured events to the ones you need to run the splat command.