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https://issues.apache.org/jira/browse/GIRAPH-259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13427285#comment-13427285
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Maja Kabiljo commented on GIRAPH-259:
-------------------------------------
As long as we document what's the way of execution, having MasterCompute being
executed before or after Vertex computes essentially differs just in the first
super step - whether algorithm starts with master or vertex compute. From what
I see, now it goes like this:
input superstep -> master compute 0 -> vertex compute 0 -> master compute 1 ->
vertex compute 1 -> ...
One thing is that master can't actually give any aggregator value to vertices
in superstep 0 since vertices didn't get a chance to call registerAggregator
before that. I guess the reason we ask aggregators to be registered on the user
is so we wouldn't have to send aggregator class to workers (or in current
implementation write it to Zookeeper)?
Here is the problem with current approach: say we have a regular (not
persistent) sum aggregator and master and vertices make the following changes
during computation:
||superstep||compute||value it sees||change||
|1|master|0|+1|
|1|vertex|1|+5|
|2|master|6|+10|
|2|vertex|15 or 16?| |
We can just define one of those, but my opinion is that it would be clearer if
vertices get executed first:
||superstep||compute||value it sees||change||
|1|vertex|0|+5|
|1|master|5|+1|
|2|vertex|6|+50|
|2|master|50|+10|
|3|vertex|60| |
And if we want to start with master compute we can have master compute
superstep -1 for example.
> TestBspBasic.testBspPageRank is broken
> --------------------------------------
>
> Key: GIRAPH-259
> URL: https://issues.apache.org/jira/browse/GIRAPH-259
> Project: Giraph
> Issue Type: Bug
> Reporter: Maja Kabiljo
> Assignee: Maja Kabiljo
> Attachments: GIRAPH-259-1.patch, GIRAPH-259-2.patch,
> GIRAPH-259-3.patch
>
>
> Test crashes on line 152 in class SimplePageRankVertex in distributed mode.
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