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https://issues.apache.org/jira/browse/HAMA-642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13456465#comment-13456465
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Thomas Jungblut commented on HAMA-642:
--------------------------------------

We could always do the hardcore database approach and save the keys in a B+ 
tree while keeping the memory consuming parts on _local_ disk. 

In HAMA-596 I've seen the adjacency list use most of the RAM. So it would 
totally make sense to check this approach, it would enable large undirected or 
even dense graphs.
Although I think it is not difficult to write a B+ Tree, I think the layout on 
disk and lookup techniques could be quite sophisticated. Can we loot out some 
frameworks that can help us on that?

Please don't come up with HBase or Accumulo, we should get this done without 
any other infrastructure burden (at least Hama itself is enough infra burden 
for most people).
                
> Make GraphRunner disk based
> ---------------------------
>
>                 Key: HAMA-642
>                 URL: https://issues.apache.org/jira/browse/HAMA-642
>             Project: Hama
>          Issue Type: Improvement
>          Components: graph
>            Reporter: Thomas Jungblut
>
> To improve scalability we can improve the graph runner to be disk based.
> Which basically means:
> - We have just a single Vertex instance that get's refilled.
> - We directly write vertices to disk after partitioning
> - In every superstep we iterate over the vertices on disk, fill the vertex 
> instance and call the users compute functions
> Problems:
> - State other than vertex value can't be stored easy
> - How do we deal with random access after messages have arrived?
> So I think we should make the graph runner more hybrid, like using the queues 
> we have implemented in the messaging. So the graphrunner can be configured to 
> run completely on disk, in cached mode or in in-memory mode.

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