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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4584) Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
Date Wed, 11 Feb 2009 23:19:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12672824#action_12672824
] 

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

Regd more complete solution, a much simpler fix could be :
 
  * BlockReport does not list the directories at all, but just sends the in-memory list of
blocks
  * Any mysteriously missing blocks would be caught by DataBlockScanner (default period 3
weeks)

Pros :
   * The simplest fix with maximum benefit
   * Good precursor to eventually removing or drastically less frequent block reports

Cons :
    * DataBlockScanner is rather slow (though the period could configured)
         ** But we have rarely seen blocks disappear. more likely there are truncated or corrupt.

This is preferred fix for this jira.

Separating heartbeat from block reports and deletions that this attached patch does could
still be useful. I am +1 having that too.. but not a requirement.


> 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
>
>
> 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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