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4.6.3. Configuring the Trace PMDA

The trace PMDA is configurable primarily through command-line options. The list of command-line options in Table 4.1, “Selected Command-Line Options” is not exhaustive, but it identifies those options which are particularly relevant to tuning the manner in which performance data is collected.

Table 4.1. Selected Command-Line Options

Access controls
The trace PMDA offers host-based access control. This control allows and disallows connections from instrumented applications running on specified hosts or groups of hosts. Limits to the number of connections allowed from individual hosts can also be mandated.
Sample duration
The interval over which metrics are to be maintained before being discarded is called the sample duration.
Number of historical buffers
The data maintained for the sample duration is held in a number of internal buffers within the trace PMDA. These are referred to as historical buffers. This number is configurable so that the rolling window effect can be tuned within the sample duration.
Counter and observation metric units
Since the data being exported by the trace.observe.value and trace.counter.count metrics are user-defined, the trace PMDA by default exports these metrics with a type of “none.” A framework is provided that allows the user to make the type more specific (for example, bytes per second) and allows the exported values to be plotted along with other performance metrics of similar units by tools like pmchart.
Instance domain refresh
The set of instances exported for each of the trace metrics can be cleared through the storable trace.control.reset metric.