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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2391) Speculative Execution race condition with output paths
Date Tue, 12 Feb 2008 07:36:12 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12567988#action_12567988
] 

Hadoop QA commented on HADOOP-2391:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
http://issues.apache.org/jira/secure/attachment/12375307/patch-2391.txt
against trunk revision 619744.

    @author +1.  The patch does not contain any @author tags.

    tests included +1.  The patch appears to include 6 new or modified tests.

    javadoc +1.  The javadoc tool did not generate any warning messages.

    javac +1.  The applied patch does not generate any new javac compiler warnings.

    release audit +1.  The applied patch does not generate any new release audit warnings.

    findbugs +1.  The patch does not introduce any new Findbugs warnings.

    core tests +1.  The patch passed core unit tests.

    contrib tests +1.  The patch passed contrib unit tests.

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/1782/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/1782/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/1782/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/1782/console

This message is automatically generated.

> Speculative Execution race condition with output paths
> ------------------------------------------------------
>
>                 Key: HADOOP-2391
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2391
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>         Environment: all
>            Reporter: Dennis Kubes
>            Assignee: Amareshwari Sri Ramadasu
>             Fix For: 0.16.1
>
>         Attachments: HADOOP-2391-1-20071211.patch, patch-2391.txt
>
>
> I am tracking a problem where when speculative execution is enabled, there is a race
condition when trying to read output paths from a previously completed job.  More specifically
when reduce tasks run their output is put into a working directory under the task name until
the task in completed.  The directory name is something like workdir/_taskid.  Upon completion
the output get moved into workdir.  Regular tasks are checked for this move and not considered
completed until this move is made.  I have not verified it but all indications point to speculative
tasks NOT having this same check for completion and more importantly removal when killed.
 So what we end up with when trying to read the output of previous tasks with speculative
execution enabled is the possibility that previous workdir/_taskid will be present when the
output directory is read by a chained job.  Here is an error when supports my theory:
> Generator: org.apache.hadoop.ipc.RemoteException: java.io.IOException: Cannot open filename
/u01/hadoop/mapred/temp/generate-temp-1197104928603/_task_200712080949_0005_r_000014_1
>         at org.apache.hadoop.dfs.NameNode.open(NameNode.java:234)
>         at sun.reflect.GeneratedMethodAccessor64.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>         at java.lang.reflect.Method.invoke(Method.java:597)
>         at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:389)
>         at org.apache.hadoop.ipc.Server$Handler.run(Server.java:644)
>         at org.apache.hadoop.ipc.Client.call(Client.java:507)
>         at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:186)
>         at org.apache.hadoop.dfs.$Proxy0.open(Unknown Source)
>         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.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
>         at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
>         at org.apache.hadoop.dfs.$Proxy0.open(Unknown Source)
>         at org.apache.hadoop.dfs.DFSClient$DFSInputStream.openInfo(DFSClient.java:839)
>         at org.apache.hadoop.dfs.DFSClient$DFSInputStream.<init>(DFSClient.java:831)
>         at org.apache.hadoop.dfs.DFSClient.open(DFSClient.java:263)
>         at org.apache.hadoop.dfs.DistributedFileSystem.open(DistributedFileSystem.java:114)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1356)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1349)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1344)
>         at org.apache.hadoop.mapred.SequenceFileOutputFormat.getReaders(SequenceFileOutputFormat.java:87)
>         at org.apache.nutch.crawl.Generator.generate(Generator.java:429)
>         at org.apache.nutch.crawl.Generator.run(Generator.java:563)
>         at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65)
>         at org.apache.hadoop.util.ToolBase.doMain(ToolBase.java:54)
>         at org.apache.nutch.crawl.Generator.main(Generator.java:526)
> I will continue to research this and post as I make progress on tracking down this bug.

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