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Date: Thu, 5 Feb 2009 19:30:03 -0800 (PST)
From: "Suresh Srinivas (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Updated: (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:all-tabpanel ]

Suresh Srinivas updated HADOOP-4584:
------------------------------------

    Attachment: 4584.patch

I have made the changes to report received block after processing every command from the queue.

@Dhruba
I have retained {{CommandQueue}} based on LinkedList. The reasons - 1. The required interface is simple 2.{{CommandQueue}} notifies based on a common object {{dataAvailable}} along with receivedBlockList.

Currently the following unit tests are failing (know failures):
- TestMapReduceLocal
- TestKillCompletedJob


> 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
>
>
> 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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