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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7964) Add support for async edit logging
Date Wed, 17 Feb 2016 18:18:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15150918#comment-15150918
] 

Daryn Sharp commented on HDFS-7964:
-----------------------------------

Thanks for the rebase.  I'm currently really busy but will get to this.  To help me more quickly
check the patch, are there any functional changes or just trivial merge conflicts?

> Add support for async edit logging
> ----------------------------------
>
>                 Key: HDFS-7964
>                 URL: https://issues.apache.org/jira/browse/HDFS-7964
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: 2.0.2-alpha
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>         Attachments: HDFS-7964-rebase.patch, HDFS-7964.patch, HDFS-7964.patch, HDFS-7964.patch,
HDFS-7964.patch
>
>
> Edit logging is a major source of contention within the NN.  LogEdit is called within
the namespace write log, while logSync is called outside of the lock to allow greater concurrency.
 The handler thread remains busy until logSync returns to provide the client with a durability
guarantee for the response.
> Write heavy RPC load and/or slow IO causes handlers to stall in logSync.  Although the
write lock is not held, readers are limited/starved and the call queue fills.  Combining an
edit log thread with postponed RPC responses from HADOOP-10300 will provide the same durability
guarantee but immediately free up the handlers.



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