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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-16) RPC call times out while indexing map task is computing splits
Date Mon, 13 Feb 2006 07:23:58 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-16?page=comments#action_12366155 ] 

Bryan Pendleton commented on HADOOP-16:
---------------------------------------

Looking further into my concern about hasTaskWithCacheHit overhead (called from obtainNewMapTask
in JobInProgress).... it looks like obtainNewMapTask actually calls hasTaskWithCacheHit once
for each map job, but always chooses the first choice - why even call the relatively expensive
hasTaskWithCacheHit if you've already chosen a value for cacheTarget? Likewise, once you've
filled in both cacheTarget and hasTarget, why not break out of that for loop entirely?

Am I following the code flow incorrectly, or is obtainNewMapTask essentially making maps^2
RPC calls in response to a single incoming RPC call? Even if the jobtracker and namenode are
running on the same host, that could easily explain the sensitivity to timeouts in the current
code.


> RPC call times out while indexing map task is computing splits
> --------------------------------------------------------------
>
>          Key: HADOOP-16
>          URL: http://issues.apache.org/jira/browse/HADOOP-16
>      Project: Hadoop
>         Type: Bug
>   Components: mapred
>  Environment: MapReduce multi-computer crawl environment: 11 machines (1 master with
JobTracker/NameNode, 10 slaves with TaskTrackers/DataNodes)
>     Reporter: Chris Schneider

>
> We've been using Nutch 0.8 (MapReduce) to perform some internet crawling. Things seemed
to be going well until...
> 060129 222409 Lost tracker 'tracker_56288'
> 060129 222409 Task 'task_m_10gs5f' has been lost.
> 060129 222409 Task 'task_m_10qhzr' has been lost.
>    ........
>    ........
> 060129 222409 Task 'task_r_zggbwu' has been lost.
> 060129 222409 Task 'task_r_zh8dao' has been lost.
> 060129 222455 Server handler 8 on 8010 caught: java.net.SocketException: Socket closed
> java.net.SocketException: Socket closed
>         at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:99)
>         at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
>         at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
>         at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)
>         at java.io.DataOutputStream.flush(DataOutputStream.java:106)
>         at org.apache.nutch.ipc.Server$Handler.run(Server.java:216)
> 060129 222455 Adding task 'task_m_cia5po' to set for tracker 'tracker_56288'
> 060129 223711 Adding task 'task_m_ffv59i' to set for tracker 'tracker_25647'
> I'm hoping that someone could explain why task_m_cia5po got added to tracker_56288 after
this tracker was lost.
> The Crawl .main process died with the following output:
> 060129 221129 Indexer: adding segment: /user/crawler/crawl-20060129091444/segments/20060129200246
> Exception in thread "main" java.io.IOException: timed out waiting for response
>     at org.apache.nutch.ipc.Client.call(Client.java:296)
>     at org.apache.nutch.ipc.RPC$Invoker.invoke(RPC.java:127)
>     at $Proxy1.submitJob(Unknown Source)
>     at org.apache.nutch.mapred.JobClient.submitJob(JobClient.java:259)
>     at org.apache.nutch.mapred.JobClient.runJob(JobClient.java:288)
>     at org.apache.nutch.indexer.Indexer.index(Indexer.java:263)
>     at org.apache.nutch.crawl.Crawl.main(Crawl.java:127)
> However, it definitely seems as if the JobTracker is still waiting for the job to finish
(no failed jobs).
> Doug Cutting's response:
> The bug here is that the RPC call times out while the map task is computing splits. 
The fix is that the job tracker should not compute splits until after it has returned from
the submitJob RPC.  Please submit a bug in Jira to help remind us to fix this.

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