Re: RFC: metric labels as first-class PCP concept

----- Original Message -----
> > [...]
> > > Downsides: Some text would be uglified (which clients can hide), and
> > 
> > You can't hide those awful instance names
> 
> Yes, you can.

Not in these cases ...

> >  - pmchart, pmval, pmie, ...  lots of the tools expect some kind of
> > meaningful instance name - and an instance name with a JSON document
> > appended to it is not that, sorry.
> 
> These tools are all shipped with PCP.  We can give them a flag, or
> even hard-code behaviour, to clip off the "@label ..." parts, as a UI
> policy matter.

(that'd be yet another compromise hack)

But you're not following.  Those tools have already shipped, sometimes
for 20+ years.  They are installed on peoples systems and the instance
names that they see (from remote hosts or newly created V.2 archives)
cannot, and will not, be turned into such a mess.  These tools will
access up-rev, remote pmcd servers for many many years, and archives
for many more.

We are not going to be appending JSON documents to instance names, it's
as flawed an idea as putting labels in metric help text.

> > > [...]  If metric labels were represented as values
> in peer metrics, rather than help text, there is no format
> archive/etc. change required.

What you're suggesting is basically the same as event metric parameters
(Ken's idea, years ago).  I considered using that here too, and in depth,
but ultimately discarded it because...

> > Labels are really a separate metadata concept.  [...] do it cleanly.

Again, they are a separate metadata concept - much closer to pmDesc fields
(analogous to inode stat(2) data in earlier filesystem extended attributes
comparison) than to full metrics.  A metric is a very heavy weight thing
(namespace, PMIDs, indoms, instances, pmDesc, help texts) - labels are not
that at all.

> You also mentioned the need to vary labels - that necessitates treating
> them as values along a timeline, just like normal metrics.

Much lighter weight though - labels are a concept closer to instances than
metrics, which also change along the same timeline.


It seems one unexplored area needing discussion is filtering.  I'll follow
up on that in a separate thread, as that is a big topic and I want to look
at filtering solutions beyond labels as well.

cheers.

--
Nathan

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