Hi Vincentius,
I'd recommend checking out the code in the call() method of this class
https://github.com/apache/giraph/blob/trunk/giraph-core/src/main/java/org/apache/giraph/graph/ComputeCallable.java
to
try to follow the logic that occurs during computation in a superstep, as
well as the code
https://github.com/apache/giraph/blob/trunk/giraph-core/src/main/java/org/apache/giraph/comm/netty/NettyWorkerClientRequestProcessor.java
for handling message sending and the execute method in GraphTaskManager
https://github.com/apache/giraph/blob/trunk/giraph-core/src/main/java/org/apache/giraph/graph/GraphTaskManager.java
which
basically handles the overall control flow of everything. I've found that
for Giraph at some point you're going to more or less need to dig through
the code to figure out what's going on behind the scenes. Looking at the
call() method and computePartition() methods in ComputeCallable are pretty
enlightening. As far as messaging goes it appears that everything is
flushed from the sender before the end of the superstep.
Someone else please correct me if I'm wrong about any of these things; I
don't want to mislead anyone.
Best,
Matthew Saltz
On Mon, Nov 10, 2014 at 12:18 PM, Vincentius Martin
vincentiusmar...@gmail.com wrote:
Hi XingFeng, thanks for your answer!
Yes, I have already read Pregel paper, unfortunately there are some
specific steps that I still couldn't grasp.
Therefore, when does the checkpoint happen? Is it before/after the step 1
(the receiving messages phase) in your explanation?
Also, according to your explanation, I can deduce that at the beginning of
each superstep, the messages are still in the sender workers' buffer and
each of the sender workers will send them at this phase. Am I right?
Regards,
Vincentius Martin
On Mon, Nov 10, 2014 at 5:49 PM, XingFENG xingf...@cse.unsw.edu.au
wrote:
Hi Vincentius Martin,
Since Giraph is based on Pregel, I would refer you to the paper *Pregel:
A System for Large-Scale Graph Processing *for more details.
Briefly speaking, in each superstep,
1. a worker (which is responsible for a partition of vertices) receives
messages from others. A worker then divided these messages according to the
destID and active vertices which have incoming messages.
2. a worker runs *compute* function of each active vertex. Meanwhile,
the *compute* function may generate messages to other vertices. These
messages are buffered, combined and sent in batches in an asynchronous way.
3. after a worker finishes *compute* function of all active vertex, it
waits for all other workers finishing their *compute* functions. What is
more, it waits for all sending tasks to finish to ensure all messages can
be received in next superstep. Then every worker goes into next superstep.
For your second problem, messages are stored in a buffer.
On Mon, Nov 10, 2014 at 6:14 PM, Puneet Agarwal puagar...@yahoo.com
wrote:
These are some very interesting questions. I also would like to know the
answers to these.
- Puneet
IIT Delhi, India
On Monday, November 10, 2014 9:30 AM, Vincentius Martin
vincentiusmar...@gmail.com wrote:
I am curious about how does Giraph receive messages before processing it
I know that they use their accepted messages in the compute() method on
the next superstep, but when do they receive it? If it is before the
checkpoint process, is there any part in the documentation/code that I can
see to understand it?
Also, what mechanism that Giraph use to store messages before superstep
S+1? Are they store it in a buffer or disk first?
I still cannot find anything about this.
Regards,
Vincentius Martin
--
Best Regards.
---
Xing FENG
PhD Candidate
Database Research Group
School of Computer Science and Engineering
University of New South Wales
NSW 2052, Sydney
Phone: (+61) 413 857 288
