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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4584) Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
Date Tue, 24 Feb 2009 05:32:02 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676189#action_12676189
] 

dhruba borthakur commented on HADOOP-4584:
------------------------------------------

I do not understand this patch very clearly, can you pl explain.

Block reports are meant to find inconsistencies between what is on disk versus what is in
the namenode metadata. A typical scenario can be that an administrator mistakenly ran a "rm
 -rf <datadir>" on a datanode. The next block report would make the namenode detect
this situation. 

Does this patch suggest that a block report is created by the datanode without scanning the
data directory on disk? more info HADOOP-1079.

> 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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