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From Andrew Chung <afchun...@gmail.com>
Subject Re: Understanding GroupCommunication terms
Date Thu, 16 Jun 2016 19:41:54 GMT
I see, thanks!

On Thursday, June 16, 2016, Dhruv Mahajan <dhruv.mahajan@gmail.com> wrote:

> Hi Andrew,
>
> So Julia is right. For a given group, a task represents one node only. But
> then if the operators task is using are from different groups then it sort
> of represents one node per group. Does that make sense?
>
> Dhruv
>
> On Thu, Jun 16, 2016 at 12:20 PM, Andrew Chung <afchung90@gmail.com
> <javascript:;>> wrote:
>
> > Seems like there are some differences in understanding here. @Dhruv could
> > you verify that a reef task can or cannot contain multiple nodes?
> >
> > Thanks,
> > Andrew
> >
> > On Thursday, June 16, 2016, Julia Wang (QIUHE) <Qiuhe.Wang@microsoft.com
> <javascript:;>>
> > wrote:
> >
> > > Short summary:
> > > A group can have multiple operators
> > > A group contains multiple nodes
> > > A task can represent multiple nodes in multiple groups case. If there
> is
> > > only one group, a task represents a node. That’s is current IMRU case.
> > > Node is a concept in typology like a tree node
> > > OperatorTopology is responsible for receiving/sending message for an
> > > operator in a group. It knows the topology like parent and children.
> > > sourceId and destId are for communication between nodes I believe
> > > One task can have multiple operators.
> > >
> > > Julia
> > >
> > > -----Original Message-----
> > > From: Dhruv Mahajan [mailto:dhruv.mahajan@gmail.com <javascript:;>
> <javascript:;>]
> > > Sent: Thursday, June 16, 2016 11:48 AM
> > > To: dev@reef.apache.org <javascript:;> <javascript:;>
> > > Subject: Re: Understanding GroupCommunication terms
> > >
> > > Hi
> > >
> > > Please find answers inline.
> > >
> > > >
> > > > 1. What is the relationship between group, operator, Node, and Task?
> > > >
> > >
> > > A group consists of set of nodes/ evaluators that need to communicated
> > > with each other. An operator like Broadast, Reduce, AllReduce specifies
> > the
> > > semantics of communication. Each node might be part of multiple groups.
> > A
> > > task can call these operators to get and send the values. So in that
> > sense
> > > when a task uses these operators task and node are sort of same thing.
> > >
> > >
> > > > 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.
> > > >
> > > Node is a logical concept. In general, One REEF task has one node only.
> > In
> > > my mind I cannot think of case where it would be otherwise.
> > >
> > >
> > > > 3. What does an `OperatorTopology` represent? To me it seems like it
> > > > represents a logical Node.
> > > >
> > > For doing these communications nodes are organized in particular
> topology
> > > (flat where master connects to all other nodes, Binary tree: where
> nodes
> > > are organized in a tree fashion, Binomial topology and so on). Each
> node
> > > needs to communicate only to its children and parents during any
> operator
> > > call (broadcast etc.). The OperatorTopology class defines the local
> > > topology for the node (children and parent) and then provide lower
> level
> > > functions to send and receive messages, do reduce on output of children
> > > etc. Each operator has its own OperatorTopology class even though they
> > > belong to same group (ideally we need only one OperatorTopology per
> > group)
> > >
> > >
> > > > 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?
> > > >
> > > Let me get back after looking at the code :)
> > >
> > >
> > >
> > > > 5. Can multiple operators reside on the same REEF Task? Multiple
> nodes?
> > > > Multiple operators can reside on same REEF task. In ML its sort of
> > > > common to do broadcast followed by reduce. Multiple groups also can
> > > > reside on same task. Node and REEf-Task are one and the same thing.
> As
> > > > I said earlier, I cannot think od the case when they will not be.
> > >
> > >
> > >
> > >
> > > > Thanks!
> > > > Andrew
> > > >
> > >
> >
>

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