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Date: Mon, 2 Feb 2009 12:15:59 -0800 (PST)
From: "Suresh Srinivas (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=12669727#action_12669727 ] 

Suresh Srinivas commented on HADOOP-4584:
-----------------------------------------

@Raghu, should we just go for a permanent solution instead of this workaround? If so, lets talk about how it should be done.

In step 4, we cannot wait for both. We are dong {{wait(1000}} against the {{receivedBlockList}}. I am not sure how we can at the same time wait against {{commandQueue}}. We have to chose one of them. Which object might get {{notify()}} of the two? BTW this wait is currently 1 second. So we keep looking for work to do every second.

@dhruba
Is is it better to process one command at a time instead of all the queued ones at once?

> 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
>
>
> 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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