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https://issues.apache.org/jira/browse/HAMA-443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13150258#comment-13150258
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Thomas Jungblut commented on HAMA-443:
--------------------------------------
Nope.
The whole messsaging is based on this modulo "hack".
You partition by the vertex name's hashcode.
So every vertex where the vertex name is % numTasks == 0 belongs to the first
task -> peerNames[0].
In case a vertex at task 2 (=peerNames[1]) has a vertex where the hashCode
buckets to peerNames[0] , it will be messaged to peerNames[0].
If the vertex is not on this task (=nullpointer exception), either the
consistency of hashCode is broken or the partitioning does not work correctly.
The lookup map is just for reverse lookup of the vertex by its name, since
there is no other choice with messaging. Yeah we could message a whole vertex,
but that is not really an overhead.
> SSSP doesn't works with multi-tasks
> -----------------------------------
>
> Key: HAMA-443
> URL: https://issues.apache.org/jira/browse/HAMA-443
> Project: Hama
> Issue Type: Bug
> Components: examples
> Affects Versions: 0.3.0
> Reporter: Edward J. Yoon
> Assignee: Thomas Jungblut
> Fix For: 0.4.0
>
> Attachments: HAMA-443.patch, HAMA-443_1.patch, HAMA-443_v2.patch,
> HAMA-443_v3.patch, HAMA-443_v4.patch, HAMA-443_v5.patch, patch.txt
>
>
> {code}
> root@Cnode1:/usr/local/src/hama-trunk# core/bin/hama jar
> examples/target/hama-examples-0.4.0-incubating-SNAPSHOT.jar sssp Klewno xx
> /user/root/edward/sssp-adjacencylist.txt
> Single Source Shortest Path Example:
> <Startvertex name> <optional: output path> <optional: path to own adjacency
> list textfile!>
> Setting default start vertex to "Frankfurt"!
> Setting start vertex to Klewno!
> Using new output folder: xx
> 11/09/26 09:46:24 INFO graph.ShortestPaths: Starting data partitioning...
> 11/09/26 09:47:12 INFO graph.ShortestPaths: Finished!
> 11/09/26 09:47:12 INFO bsp.BSPJobClient: Running job: job_201109260929_0004
> 11/09/26 09:47:15 INFO bsp.BSPJobClient: Current supersteps number: 0
> 11/09/26 09:47:21 INFO bsp.BSPJobClient: Current supersteps number: 1
> 11/09/26 09:47:33 INFO bsp.BSPJobClient: The total number of supersteps: 1
> Job Finished in 21.553 seconds
> -------------------- RESULTS --------------------
> java.lang.NullPointerException
> at
> org.apache.hama.examples.graph.ShortestPathsBase.printOutput(ShortestPathsBase.java:93)
> at
> org.apache.hama.examples.graph.ShortestPaths.main(ShortestPaths.java:239)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at
> org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:68)
> at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:139)
> at org.apache.hama.examples.ExampleDriver.main(ExampleDriver.java:37)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at org.apache.hama.util.RunJar.main(RunJar.java:145)
> {code}
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