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Re: [pcp] RFC: fetchgroup api

To: Mark Goodwin <mgoodwin@xxxxxxxxxx>
Subject: Re: [pcp] RFC: fetchgroup api
From: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Date: Thu, 26 Nov 2015 11:38:20 -0500
Cc: pcp developers <pcp@xxxxxxxxxxx>
Delivered-to: pcp@xxxxxxxxxxx
In-reply-to: <5656970C.10103@xxxxxxxxxx>
References: <20151125064821.GA27272@xxxxxxxxxx> <5656970C.10103@xxxxxxxxxx>
User-agent: Mutt/1.4.2.2i
Hi, Mark -

> Hi Frank, I like this API - have a few questions and suggestions. 

Thanks a lot for looking into it!

> To begin with, for the case where we make several calls to
> pmExtendFetchGroup_indom for several different metrics with the same
> instance domain and the same fetch group, the returned instance
> domains should match up, right?

Yes, generally.

> e.g. for proc metrics, which are pretty dynamic, that doesn't seem
> to be happening - but maybe I'm missing something ...

I ran your program, ramped up proc/pid churn, and saw a few  
    FAIL("nrss != nvss")
entries hit.  Run under the debugger, it's clear that pmFetch
itself returned resultsets with different numbers of values 
(see *fg->prevResult->vset[0] vs. [1] vs [2]).  The inconsistent
results originated from pmdaproc.  fetchgroup can't be blamed.
pmdaproc's "refresh" logic is probably to blame here, if indeed
there is any blame to place.

- FChE

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