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2.4. Other Issues

Other issues include extracting the information, latency and threads of control, Name Space, PMDA help text, and management of evolution within a PMDA.

2.4.1. Extracting the Information

A suggested approach to writing a PMDA is to write a standalone program to extract the values from the target domain and then incorporate this program into the PMDA framework. This approach avoids concurrent debugging of two distinct problems:
  • Extraction of the data
  • Communication with PMCD
These are some possible ways of exporting the data from the target domain:
  • Accumulate the performance data in a public shared memory segment.
  • Write the performance data to the end of a log file.
  • Periodically rewrite a file with the most recent values for the performance data.
  • Implement a protocol that allows a third party to connect to the target application, send a request, and receive new performance data.
  • If the data is in the operating system kernel, provide a kernel interface (preferred) to export the performance data.
Most of these approaches require some further data processing by the PMDA.