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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4186) logSync() is called with the write lock held while releasing lease
Date Wed, 14 Nov 2012 13:22:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13497082#comment-13497082
] 

Kihwal Lee commented on HDFS-4186:
----------------------------------

It's modtly an optimization. Since several methods are now calling logSync() even if there
is nothing to sync,it allows returning early before hitting the edit log lock. There is no
correctness problem without it in terms of edit logging, but the metric for batched sync will
be inaccurate. 
                
> logSync() is called with the write lock held while releasing lease
> ------------------------------------------------------------------
>
>                 Key: HDFS-4186
>                 URL: https://issues.apache.org/jira/browse/HDFS-4186
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.23.4, 2.0.2-alpha
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Critical
>         Attachments: hdfs-4186-trunk.patch
>
>
> As pointed out in HDFS-4138, when the lease monitor calls internalReleaseLease(), it
acquires the namespace write lock. Inside internalReleaseLease(), if a block recovery is needed,
the lease is reassigned to the namenode itself and this is logged & synced in logReassignLease().
> Since this is done while the write lock is held, log syncing is blocked. When a large
number of leases are expired and blocks are recovered, namenode can slow down.

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