On 23/07/16 23:17, Marko Myllynen wrote:
...
If we think metrics with PM_INDOM_NULL as one-dimensional metrics,
metrics with instance domains as two-dimensional metrics, and these
metrics which have two dynamic dimensions as three-dimensional metrics,
are there other such "3D" metrics in standard / often used PMDAs
present already, how are they set up?
There is a longish and I think complete discussion on this topic in a
mail thread earlier this year ... see
http://www.pcp.io/pipermail/pcp/2016-May/010387.html
I don't see this any kind of issue here. The case that a component must
begin with an alphabetic is documented in pmns(5) but for some reason
it is not checked/forced and in fact everything seemed to work with
components beginning with a digit.
I believe the implementation matches the documentation, namely name
components must begin with an alphabetic ... I've tried a couple of test
cases and this assertion seems to hold, so I'd be keen to see evidence
to the contrary.
I forgot another biggie yesterday - related to the persistence of PMIDs.
Its important to a number of the client tools (pmlogger, pmie, pmchart,
hmmm pretty much all actually) that if pmcd is restarted, metrics return
with the same PMID as before (this is pretty much part of the protocol
over-the-wire, and its also necessary on-disk between archives of the
same host).
This becomes very difficult to ensure in the case of dynamic metrics -
it was the main reason we switch cgroups to using this model IIRC. And
the pmdaCache interfaces support persisting instance identifiers well of
course.
As I said yesterday in email, pmdaCache can also be used to ensure
persistent mapping from dynamic metric names to PMIDs.
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