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RE: [tao-users] Load balancing question

Thanks, it seem that the algorithm, or at least how it's interacting with the standard CORBA behavior seems quite reasonable.

I didn't think of the fact that if the client ORB receives a TRANSIENT it would go to the load manager for a second try and if you add awareness to the load manager that the same dead replica is not used it would definitly be good enough!
Thanks,

/Jesper 

-----Original Message-----
From: Ossama Othman [mailto:ossama@dre.vanderbilt.edu] 
Sent: den 23 april 2005 20:08
To: Jesper S�derlund
Cc: tao-users@cse.wustl.edu
Subject: Re: [tao-users] Load balancing question

Hi Jesper,

Sorry for the delay.

On Mon, 2005-04-11 at 22:12 +0200, Jesper S�derlund wrote:
> The load balancing algorithm implemented by TAO, how does it cope with 
> the disapearance of a replica?

It currently does not.  The LoadManager currently assumes that all group members are reachable.  However, it should be relatively straightforward to implement a simple heartbeat/ping mechanism that is configurable at run-time through the PortableGroup PropertyManager interface.

> Would it not, until it itself found out that the replica was gone, 
> redirect clients to a "dead" node? How can the clients cope with this 
> gracefully?

Currently, the LoadManager could potentially redirect the client to a dead node.  If the client cannot connect to the group member (e.g. a CORBA::TRANSIENT condition), I believe that the client side ORB should redirect the request back to the previous location, which in this case is the LoadManager.  Once redirected back to the LoadManager, the LoadManager will reassign the client request to another group member.
The same goes for other non-fatal exceptions, such as CORBA::OBJ_ADAPTER and CORBA::NO_RESPONSE.

Fatal exceptions must be handled by the client as they normally would without load balancing.  Fatal exception handling related to dead nodes will be mitigated once the dead node detection support is added to the LoadManager.  However, the client should still be able to handle fatal exceptions with or without load balancing.

We'll try to add support for dead member detection ASAP since the client could potentially be bounced back and forth from and to the LoadManager, respectively, indefinitely if there is only one member in the load balanced object group.

I'll add this discussion to a related bug entry in our BTS here:

	http://deuce.doc.wustl.edu/bugzilla/show_bug.cgi?id=1365

Please feel free to add yourself to the CC list on the above bug entry.

-Ossama
--
Ossama Othman <ossama@dre.vanderbilt.edu>


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4/23/2005 9:48:30 PM
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