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2.2.4. Caching PMDA

When either the cost or latency associated with collecting performance metrics is high, the PMDA implementer may choose to trade off the currency of the performance data to reduce the PMDA resource demands or the fetch latency time.
One scheme for doing this is called a caching PMDA, which periodically instantiates values for the performance metrics and responds to each request from PMCD with the most recently instantiated (or cached) values, as opposed to instantiating current values on demand when the PMCD asks for them.
The Cisco PMDA is an example of a caching PMDA. For additional information, see the contents of the ${PCP_PMDAS_DIR}/cisco directory and the pmdacisco(1) man page.