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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-4584) Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
Date Fri, 27 Feb 2009 23:13:12 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-4584?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

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

    Attachment: 4584.hbthread.patch

Updated patch for separating heartbeat thread. Methods {{FSDataset.getCapacity(), FSDataset.getDfsUsed(),
FSDataset.getRemaining()}} use commands such as {{df}} and {{du}} on data directories and
does not need to be synchronized with FSVolumeSet.

Changes are:
* Removed synchronizing {{FSVolumeSet.getCapacity()}} on {{FSVolumeSet}}
* Removed synchronizing {{FSVolumeSet.getRemaining()}} on {{FSVolumeSet}}
* Access to {{FSDataset.getCapacity(), FSDataset.getRemaining(), FSDataset.getDfsUsed()}}
are synchronized

Note if {{df}} operation blocks, the heartbeat thread will be blocked. However assuming it
will be much shorter than 10 minutes and the datanodes will not be marked dead by namenodes.


> 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.hbthread.patch, 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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