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Re: [pcp] [PATCH] PCP pidstat PMDA

To: pcp@xxxxxxxxxxx
Subject: Re: [pcp] [PATCH] PCP pidstat PMDA
From: Ken McDonell <kenj@xxxxxxxxxxxxxxxx>
Date: Wed, 22 Apr 2015 08:29:45 +1000
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References: <5534C680.2020709@xxxxxxxxxx> <493537984.3276058.1429528962326.JavaMail.zimbra@xxxxxxxxxx> <5534EBA8.4030509@xxxxxxxxxx> <1644393599.3651017.1429563442835.JavaMail.zimbra@xxxxxxxxxx> <55364606.1000503@xxxxxxxxxx>
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On 21/04/15 22:43, Marko Myllynen wrote:
...
hmm, so it is possible to provide a redirected metric from another
domain in C but is there a way to do that in Perl or Python? And is it
possible to read a metric from another domain to be used to calculate or
construct a new metrics in the current domain, not just redirect?

In general this is not possible.

Think about the flow of a request (you're building pmda A and pmda B has the metrics you're interested in):

client -> pmcd -> pmda A -> ???

If pmda A tries to use pmcd to get to pmcd B we have a callback into pmcd and all sorts of timeout headaches ... pmie in "secret agent mode" for the summary PMDA does this, but I would not recommend that as a precedent to be copied!

If pmda B has some non-pcp export channel (as well) that could be used.

Otherwise, source code replication from pmda B into pmda A is likely to be the simplest (and most efficient) strategy.


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