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Re: [pcp] braindump on unified-context / live-logging

To: Max Matveev <makc@xxxxxxxxx>
Subject: Re: [pcp] braindump on unified-context / live-logging
From: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Date: Fri, 10 Jan 2014 14:05:25 -0500
Cc: pcp developers <pcp@xxxxxxxxxxx>
Delivered-to: pcp@xxxxxxxxxxx
In-reply-to: <21198.38090.179929.552608@xxxxxxxxxxxx>
References: <20140108013956.GG15448@xxxxxxxxxx> <21198.38090.179929.552608@xxxxxxxxxxxx>
User-agent: Mutt/1.4.2.2i
Hi, Max -

>  fche> 1.1) pmlogger needs to learn to write its output with what IIRC kenj
>  fche> has referred to as "semantic units", ie., proper use sequencing of
>  fche> write(2), fdatasync(), to put interdependent data on disk correctly.
> 
> This was the biggest bugbear of NAS Manager (for those who remember)
> which tried to provide historical and live data using archives as main
> source of information. [...]

(A little more of the history would be great.)


> What would happen if pcp client is using PM_CONTEXT_HOST with new
> protocol? Will it be banned or will it be silently dropped back to
> current "live" sematic?

Certainly.  The new protocol would just carry across the optional
pmSetMode bits, which for PM_CONTEXT_HOST would still default to
PM_MODE_LIVE.  No visible change in behavior.


- FChE

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