Re: systemtap/pcp integration

[fche at redhat dot com (Frank Ch. Eigler)]

nathans wrote:

> Got it.  So, next I'm wondering... what is [the module name] doing
> here, in this interface between systemtap/pcp?  [...]

systemtap is not a single bundle of instrumentation.  It is a tool for
building/running many instrumentation scripts.  The unique module name
lets the kernel tell them apart.


> In MMV (and the existing pmdammv, in particular), the basename of
> these files is used to form the first component of the metric
> namespace [...]

That's a most straightforward possibility, though not the most
user-friendly one, as the module names change from run to run.
Perhaps the systemtap script could propose a pmns prefix via an
auxiliary file.


> [...]  I guess you'd have to then completely start over again [for
> JSON]

Yes, but the systemtap side of this would be pretty trivial.  Printing
JSON strings is easy.


>  (for ... reasons?) 

Other messages in the thread pointed out some reasons, namely:

- ability to generalize to event traffic, not just sampled metrics
- robustness, by avoiding fragile C code


> [...]  I haven't seen any other need for a generic JSON interface
> [...]

In previous notes it was pointed out that JSON is a good encoding for
stats data, because it is exported by other tools like ceph, zabbix,
and many others including

> [...] elasticsearch [...]

So the proposal is to think about a single general JSON PMDA that can
be configured to bridge data from multiple JSON-emitting applications,
including systemtap scripts.


- FChE