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Date: Tue, 24 Feb 2009 11:03:02 -0800 (PST)
From: "Raghu Angadi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4584) Slow generation of blockReport at
 DataNode causes delay of sending heartbeat to NameNode
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    [ https://issues.apache.org/jira/browse/HADOOP-4584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676364#action_12676364 ] 

Raghu Angadi commented on HADOOP-4584:
--------------------------------------

> Creeping inconsistency bugs in the NN seem to make very accurate block reports a precious commodity, one that I'd gladly pay an expensive scan for (though I agree that once an hour is probably excessive).

FYI : none of the NN inconsistencies in recent times we caught or fixed by disk scans in block reports.

> Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
> ----------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4584
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4584
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Hairong Kuang
>            Assignee: Suresh Srinivas
>             Fix For: 0.20.0
>
>         Attachments: 4584.patch, 4584.patch, 4584.patch, 4584.patch, 4584.patch, 4584.patch
>
>
> sometimes due to disk or some other problems, datanode takes minutes or tens of minutes to generate a block report. It causes the datanode not able to send heartbeat to NameNode every 3 seconds. In the worst case, it makes NameNode to detect a lost heartbeat and wrongly decide that the datanode is dead.
> It would be nice to have two threads instead. One thread is for scanning data directories and generating block report, and executes the requests sent by NameNode; Another thread is for sending heartbeats, block reports, and picking up the requests from NameNode. By having these two threads, the sending of heartbeats will not get delayed by any slow block report or slow execution of NameNode requests.

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