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Re: pcp updates - slow start PMDAs

To: Ken McDonell <kenj@xxxxxxxxxxxxxxxx>, pcp@xxxxxxxxxxx
Subject: Re: pcp updates - slow start PMDAs
From: Martins Innus <minnus@xxxxxxxxxxx>
Date: Tue, 08 Apr 2014 15:52:23 -0400
Cc: "Eigler, Frank" <fche@xxxxxxxxxx>
Delivered-to: pcp@xxxxxxxxxxx
In-reply-to: <5341E094.5090304@xxxxxxxxxxxxxxxx>
References: <5341E094.5090304@xxxxxxxxxxxxxxxx>
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Ken,

On 4/6/14 7:17 PM, Ken McDonell wrote:
This commit will allow all PMDAs (C, Perl and Python) to get early access to 
pmdaConnect().

This should avoid most of the slow start issues where a PMDA is launched but 
takes some time to discover what metrics and/or instance domains are available 
... if this process takes too long, pmcd will assume the initial credentials 
handshake has timed out and the PMDA will not be a happy camper thereafter.

By giving the PMDA developer the option to connect to pmcd sooner, this problem 
is largely avoided.

What remains is the slow PMDA issue where a subsequent PDU request from a PMAPI client is 
received from pmcd while the PMDA is "busy" (including slow start) ... this 
requires much more serious surgery to fix.

If you've been seeing PMDAs not starting (perhaps sometimes, not all times), 
this change should help ... feedback and confirmation of this hypothesis would 
be most valuable.


Based on some initial testing, my slow start case in perl appears to be fixed with this change, thanks very much for fixing this! I'm not sure yet if I will hit the other problem you mention. I will have to do some more testing.

Thanks again.

Martins

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