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Re: JSON PMDA (was Re: [pcp] PCP JMX PMDA)

To: Nathan Scott <nathans@xxxxxxxxxx>, Marko Myllynen <myllynen@xxxxxxxxxx>
Subject: Re: JSON PMDA (was Re: [pcp] PCP JMX PMDA)
From: David Smith <dsmith@xxxxxxxxxx>
Date: Tue, 26 Apr 2016 13:41:03 -0500
Cc: pcp developers <pcp@xxxxxxxxxxx>
Delivered-to: pcp@xxxxxxxxxxx
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On 04/26/2016 01:41 AM, Nathan Scott wrote:
> Hi guys,
> 
> ----- Original Message -----
>> [...]
>>>> * metadata.json updates are not picked up during JSON PMDA lifetime
>>>
>>> Yes, that is true. As far as I know, that's fairly standard for PMDAs,
>>> especially python ones.
>>
>> Ok, Nathan mentioned earlier that the Python PMDA API was extended to
>> allow adding metrics dynamically so if metadata.json updates are not
>> picked up then on the fly then perhaps he meant something else.
> 
> I was referring to all the work David did to allow metrics to be defined
> dynamically for python PMDAs (i.e. such that add_metric() can be called
> after the PMDA enters its run() routine ... see commit ddfdbf144982bb1).
> 
> I'm a little surprised its not more dynamic than it is.  MMV handles the
> dynamic addition and removal of metrics, and I thought pmdajson did that
> too - apologies, my mistake there (I'd assumed this would be needed/used
> for the systemtap support?).  It is indeed relatively uncommon though as
> David says, to have that level of flexibility in any PMDA.

As I mentioned in my other email, I was wrong here. The JSON pmda does
handle dynamic addition and removal of metadata files. However, it
doesn't handle changes to an existing metadata file.

-- 
David Smith
dsmith@xxxxxxxxxx
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)

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