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From "Dmytro Molkov (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-599) Improve Namenode robustness by prioritizing datanode heartbeats over client requests
Date Wed, 26 May 2010 21:03:52 GMT

     [ https://issues.apache.org/jira/browse/HDFS-599?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dmytro Molkov updated HDFS-599:
-------------------------------

    Attachment: HDFS-599.3.patch

Please have a look. I addressed Hairong's comments for the previous patch.
I will create additional Jiras for the rest of the comments in the conversation.

@Hairong as far as TestDistributedFileSystem is concerned it was more of a problem of svn
diff command. The actual change is really small. I added one more test case which reruns other
testcases with service port on. A little is done to make it work, like each testcase instead
of constructing new HdfsConfiguration calls a method that based on the dualPortTesting boolean
flag creates a conf with service port configuration turned on.

> Improve Namenode robustness by prioritizing datanode heartbeats over client requests
> ------------------------------------------------------------------------------------
>
>                 Key: HDFS-599
>                 URL: https://issues.apache.org/jira/browse/HDFS-599
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: Dmytro Molkov
>         Attachments: HDFS-599.3.patch, HDFS-599.patch
>
>
> The namenode processes RPC requests from clients that are reading/writing to files as
well as heartbeats/block reports from datanodes.
> Sometime, because of various reasons (Java GC runs, inconsistent performance of NFS filer
that stores HDFS transacttion logs, etc), the namenode encounters transient slowness. For
example, if the device that stores the HDFS transaction logs becomes sluggish, the Namenode's
ability to process RPCs slows down to a certain extent. During this time, the RPCs from clients
as well as the RPCs from datanodes suffer in similar fashion. If the underlying problem becomes
worse, the NN's ability to process a heartbeat from a DN is severly impacted, thus causing
the NN to declare that the DN is dead. Then the NN starts replicating blocks that used to
reside on the now-declared-dead datanode. This adds extra load to the NN. Then the now-declared-datanode
finally re-establishes contact with the NN, and sends a block report. The block report processing
on the NN is another heavyweight activity, thus casing more load to the already overloaded
namenode. 
> My proposal is tha the NN should try its best to continue processing RPCs from datanodes
and give lesser priority to serving client requests. The Datanode RPCs are integral to the
consistency and performance of the Hadoop file system, and it is better to protect it at all
costs. This will ensure that NN  recovers from the hiccup much faster than what it does now.

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