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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4183) Throttle block recovery
Date Tue, 13 Nov 2012 23:10:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13496649#comment-13496649
] 

Aaron T. Myers commented on HDFS-4183:
--------------------------------------

I personally prefer adding jitter to the lease expiration times. The trouble with throttling
lease recovery is that if we choose a value that's too low then over time outstanding leases
will build up in the NN if the rate of abandoned leases exceeds the throttling rate.
                
> Throttle block recovery
> -----------------------
>
>                 Key: HDFS-4183
>                 URL: https://issues.apache.org/jira/browse/HDFS-4183
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.23.4, 2.0.2-alpha
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Critical
>
> When a large number of files are abandoned without closing, a storm of lease expiration
follows in about an hour (lease hard limit). For the last block of each file, block recovery
is initiated and when the datanode is done, it calls commitBlockSynchronization() is called
against namenode. A burst of these calls can slow down namenode considerably. We need to throttle
block recovery and/or speed up the rate at which commitBlockSynchronization() is served.

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