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

"Nathan Scott" <[email protected]>
Newsgroups gmane.comp.sysutils.pcp
Message-ID <[email protected]>

----- Original Message -----
> > [...]  OK, see attached patch - v2.  This is a fairly large update,
> > starting to spec out more of the PMDA side of things now as well and
> > incorporate the feedback so far.
> 
> Thank you, you're obviously working hard on this.  You have sketched out
> more aspects of the representation and a couple aspects of data flow.
> 
> > (not yet profiles or archives though)
> 
> The profiles part is important, [...]

Yes, of course (as are archives), that was why I mentioned 'em as not
here yet.

> This looks very simple, which is good.

Its very lightweight too, which is great.

> how do you imagine this
> being used by tools [...] not simply
> to call pmLookupLabels() after every pmFetch() - that'd be huge new
> overhead.

FWLIW, that "huge overhead" is essentially what you're half-proposing
(although inline in the fetch, not after-the-fact - but same overhead
otherwise).

So, definitely not that.  The model is more like handling instances as
(if) they change, as I mentioned before several times now.

> [...] the PMCD_LABEL_CHANGE pmFetch
> result-flag indicating any labeling change?

Yes, at this stage - label change seems sufficiently infrequent a thing
that this may well a good approach.  That's the plan for the initial
prototype anyway, and will evaluate it then.  Its not hard to imagine
how that will look on the pmda/pmcd side, so I've left that as just an
implementation detail for now, not needing explicit design docs.

> > - switches space-separated name=value pairs to JSONB
> 
> What does "JSONB" mean in this context?

It's clearly defined in pmlabel(1) from the patch...

SYNTAX
Labels are stored and communicated within PCP using JSONB format.  This
format  is  a  restricted  form of JSON suitable for indexing and other
operations.  In JSONB form, insignificant whitespace is discarded,  and
the  order  of object keys is not preserved.  Duplicate object keys are
not kept - the later value for a given key is the only one stored.


cheers.

--
Nathan

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