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Re: [pcp] Dynamic PMDA cluster - proposal

To: Ken McDonell <kenj@xxxxxxxxxxxxxxxx>
Subject: Re: [pcp] Dynamic PMDA cluster - proposal
From: Martin Hicks <mort@xxxxxxx>
Date: Tue, 8 Jun 2010 07:25:16 -0500
Cc: Corneliu Boac <cboac@xxxxxxx>, pcp@xxxxxxxxxxx
In-reply-to: <1275968673.3803.151.camel@xxxxxxxxxxxxxxxx>
References: <4C07DC70.2030700@xxxxxxx> <1275866862.3803.120.camel@xxxxxxxxxxxxxxxx> <4C0D4D71.9080309@xxxxxxx> <1275946258.3803.133.camel@xxxxxxxxxxxxxxxx> <4C0D6742.8070004@xxxxxxx> <1275968673.3803.151.camel@xxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.17 (2007-11-01)
On Tue, Jun 08, 2010 at 01:44:33PM +1000, Ken McDonell wrote:
> 
> Something does not "feel right" about closing sockets as a signal
> mechanism ... I would have thought that the protocol between the pmda

The reconfiguration was added after the initial creation of the PMDA, so
it may have been "tacked-on" in the easiest way possible.

I'm not really against changing the protocol, if it makes the PMDA work
better.

mh

> and the daemons could be extended to make it more synchronous on each
> socket something like ...
> 
> pmda  pdu             daemon
>                       connect
> accept
>       <-config_req
>       ->config
>       <-data update
>       ->ack_ok                The ack contains state change info
>                               ok means no change
>       <-data update
>       ->ack_ok
>       <-data update
>       ->ack_new_config        pmda wants daemon to get new config info
>       <-config_req
>       ->config
>       <-data update
>       ->ack_new_config
>       <-config_req
> [now if pmda holds off sending the config pdu, the daemon has effectively
> been stopped from pushing updates]
>       ->config                sometime later, let the daemon run again
> 
> I know you did not want to muck with this protocol, but I think making
> this sort of change will give you a more robust implementation as the
> sender always knows how long to wait and the receiver does not need to
> do anything until a pdu is received.  

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