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Re: Local context vs dynamic namespace

To: kenj@xxxxxxxxxxxxxxxx
Subject: Re: Local context vs dynamic namespace
From: Nathan Scott <nathans@xxxxxxxxxx>
Date: Wed, 14 Apr 2010 09:23:58 +1000 (EST)
Cc: pcp <pcp@xxxxxxxxxxx>
In-reply-to: <1271199338.24244.278.camel@xxxxxxxxxxxxxxxx>
----- "Ken McDonell" <kenj@xxxxxxxxxxxxxxxx> wrote:

> On Wed, 2010-04-14 at 08:02 +1000, Nathan Scott wrote:
> No real issue with this, but a few comments.
> 1. By "drop a file" I presume you're thinking one file per pmda that
> wants to play, and then "somewhere" in libpcp I process all of the
> files

Right, that was what I was thinking.

> in the magic directory.  This means update is file replacement,
> rather
> than the edit and update a common file model that is much more error
> prone.

Right.  Someday, pmcd could perhaps take a leaf out of this book,
but way beyond scope here.

> 4. Should we retire the $PMDA_LOCAL_PROC and $PMDA_LOCAL_SAMPLE
> controls
> that influence when the proc and sample metrics might be available
> for
> PM_CONTEXT_LOCAL?  I think they are passed their use-by date, so
> would
> not worry if they were quietly forgotten about.

I'd be happy with that too, yep.

> 5. A lot cleaner than all of this would be an extended pmcd.conf
> format
> that included a "pick me for PM_CONTEXT_LOCAL" flag ... there is
> space
> to do that at the end of the dso line (no arguments for dsos). This
> would be
>       - system wide
>       - at the discretion of the pmda install script
>       - atomic with pmda install/remove
>       - no environment variables

Mmm, yes, nice idea - do we even need to extend the format?  Just say
any dso pmda listed in pmcd.conf is auto-loaded for local context?
With the clear/add/del a programmer can still fine tune their needs,
if they really just want particular PMDAs for a specialised tool.

This all means you have to parse pmcd.conf in libpcp, which is a bit
more involved perhaps than walking a directory and using the existing
(-K) parser code ... but, you choose, I'd be happy with either way.



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