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2.4.4. PMDA Help Text

For each metric defined within a PMDA, the PMDA developer is strongly encouraged to provide both terse and extended help text to describe the metric, and perhaps provide hints about the expected value ranges.
The help text is used to describe each metric in the visualization tools and pminfo with the -T option. The help text, such as the help text for the simple PMDA in Example 2.14, “Help Text for the Simple PMDA”, is specified in a specially formatted file, normally called help. This file is converted to the expected run-time format using the newhelp command; see the newhelp(1) man page. Converted help text files are usually placed in the PMDA's directory below ${PCP_PMDAS_DIR} as part of the PMDA installation procedure.

Example 2.14. Help Text for the Simple PMDA

The two instance domains and five metrics have a short and a verbose description. Each entry begins with a line that starts with the character “@” and is followed by either the metric name (simple.numfetch) or a symbolic reference to the instance domain number (SIMPLE.1), followed by the short description. The verbose description is on the following lines, terminated by the next line starting with “@” or end of file:
@ SIMPLE.0 Instance domain “colour” for simple PMDA
Universally 3 instances, “red” (0), “green” (1) and “blue” (3).

@ SIMPLE.1 Dynamic instance domain “time” for simple PMDA
An instance domain is computed on-the-fly for exporting current time
information. Refer to the help text for simple.now for more details.

@ simple.numfetch Number of pmFetch operations.
The cumulative number of pmFetch operations directed to “simple” PMDA.

This counter may be modified with pmstore(1).

@ simple.color Metrics which increment with each fetch
This metric has 3 instances, designated “red”, “green” and “blue”.

The value of the metric is monotonic increasing in the range 0 to
255, then back to 0.  The different instances have different starting
values, namely 0 (red), 100 (green) and 200 (blue).

The metric values my be altered using pmstore(1).

@ simple.time.user Time agent has spent executing user code
The time in seconds that the CPU has spent executing agent user code.

@ simple.time.sys Time agent has spent executing system code
The time in seconds that the CPU has spent executing agent system code.

@ simple.now Time of day with a configurable instance domain
The value reflects the current time of day through a dynamically
reconfigurable instance domain.  On each metric value fetch request,
the agent checks to see whether the configuration file in
${PCP_PMDAS_DIR}/simple/simple.conf has been modified - if it has then
the file is re-parsed and the instance domain for this metric is again
constructed according to its contents.

This configuration file contains a single line of comma-separated time
tokens from this set:
  “sec”  (seconds after the minute),
  “min”  (minutes after the hour),
  “hour” (hour since midnight).

An example configuration file could be:  sec,min,hour
and in this case the simple.now metric would export values for the
three instances “sec”, “min” and “hour” corresponding respectively to
the components seconds, minutes and hours of the current time of day.

The instance domain reflects each token present in the file, and the
values reflect the time at which the PMDA processes the fetch.