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From Markus Weimer <>
Subject Re: Understanding GroupCommunication terms
Date Thu, 16 Jun 2016 18:44:03 GMT

On 2016-06-16 11:01, Andrew Chung wrote:
> 1. What is the relationship between group, operator, Node, and Task?

Node and Task are synonymous. People just call things Nodes in the MPI 
literature, we have Tasks.

An operator is one of the primitives offered: BROADCAST, REDUCE, ... .

A communications group is a collection of Tasks with operators. IMRU 
only used one of those. But it is conceivable to have multiple groups 
orchestrated by the same Driver.

> 2. Is `Node` a logical or a physical concept? i.e. can a REEF Task
> contain multiple Nodes? My understanding is that it is a logical
> concept.

Yes, I think so.

> 3. What does an `OperatorTopology` represent? To me it seems like it
> represents a logical Node.

It represents the relationship between Tasks on the Driver: E.g. which 
Task sends its REDUCE input to which, or how BROADCASTs get sent. It is 
typically some sort of tree.

> 4. In `GroupCommunicationMessage`, what is are `sourceId` and
> `destId`? Are they a logical or a physical concept? Do they map to
> Nodes, Tasks, or operators?

I don't know, but would suspect them to identify the Tasks participating 
in the communication.

> 5. Can multiple operators reside on the same REEF Task? Multiple nodes?

Yes. For example, in IMRU, the UpdateTask and MapTask both take part in 
the REDUCE and BROADCAST operators.


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