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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3517) The last InMemory merge may be missed
Date Thu, 12 Jun 2008 04:44:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12604412#action_12604412
] 

Arun C Murthy commented on HADOOP-3517:
---------------------------------------

Ah! I see that findbugs complains that numPendingRequests is also synchronized on ShuffleRamManager
66% of the time, that shouldn't matter since it's guarded by ShuffleRamManager.dataAvailable
100% of the time. *smile*

> The last InMemory merge may be missed
> -------------------------------------
>
>                 Key: HADOOP-3517
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3517
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.18.0
>            Reporter: Devaraj Das
>            Assignee: Arun C Murthy
>            Priority: Blocker
>             Fix For: 0.18.0
>
>         Attachments: HADOOP-3517_1_20080610.patch, HADOOP-3517_2_20080611.patch, HADOOP-3517_2_20080611.patch
>
>
> This is post HADOOP-3366. The inmem merge thread has the loop:
> {code}
>         while (!exitInMemMerge) {
>             ramManager.waitForDataToMerge();
>             doInMemMerge();
>           }
> {code}
> The fetchOutputs, at the end of copying everything, does the following:
> {code}
>         exitInMemMerge = true; 
>         ramManager.close();
> {code}
> Now if the merge thread is doing a merge (inside the doInMemMerge method) when the exitInMemMerge
is set to true, the loop will break and the last merge of the files that got shuffled recently
will be skipped. ramManager.close(), that internally does a final notify to the merge thread
also won't have any effect in this case.

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