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4.6. Trace PMDA Design

Trace PMDA design covers application interaction, sampling techniques, and configuring the trace PMDA.

4.6.1. Application Interaction

Figure 4.3, “Trace PMDA Overview” describes the general state maintained within the trace PMDA.
Trace PMDA Overview

Figure 4.3. Trace PMDA Overview

Applications that are linked with the libpcp_trace library make calls through the trace Application Programming Interface (API). These calls result in interprocess communication of trace data between the application and the trace PMDA. This data consists of an identification tag and the performance data associated with that particular tag. The trace PMDA aggregates the incoming information and periodically updates the exported summary information to describe activity in the recent past.
As each protocol data unit (PDU) is received, its data is stored in the current working buffer. At the same time, the global counter associated with the particular tag contained within the PDU is incremented. The working buffer contains all performance data that has arrived since the previous time interval elapsed. For additional information about the working buffer, see Section 4.6.2.2, “Rolling-Window Periodic Sampling”.