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Re: JSON PMDA

To: David Smith <dsmith@xxxxxxxxxx>
Subject: Re: JSON PMDA
From: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Date: Thu, 16 Apr 2015 11:28:34 -0400
Cc: Nathan Scott <nathans@xxxxxxxxxx>, pcp@xxxxxxxxxxx
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In-reply-to: <552FD368.6030602@xxxxxxxxxx>
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Hi, David -

> [...]
> That sounds good, except in the case where when the JSON PMDA was
> started there were 3 JSON sources, and during the run a 4th was added.
> Now the JSON PMDA gets restarted 

...  but according to normal practice, a "restarted pmda" means
"restarted pmcd", which means active pcp contexts are dropped, which
means clients are to reconnect & recalculate name->pmid mappings.


> In case the above isn't clear, let's say that on startup the JSON PMDA
> sees the following sources:
>   bar (cluster #1), foo (cluster #2), zoo (cluster #3)
> Then the following gets added:
>   dog (cluster #4)
>
> Then the PMDA gets restarted. A sort of the pathnames would give:
>   bar (cluster #1), dog, (cluster #2), foo (cluster #3), zoo (cluster #4)

Yes, or the same sort of thing (for pmid "instance" numbers) if the
contents of the metadata files change across a pmda/pmcd restart.  Or
if the indoms inside the data files drastically.


My point is that this may not be worth protecting against.


- FChE

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