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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4584) Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
Date Mon, 02 Feb 2009 20:15:59 GMT

    [ 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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