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Date: Wed, 20 Jan 2010 13:50:54 +0000 (UTC)
From: "Hudson (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-822) Appends to already-finalized blocks
 can rename across volumes
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    [ https://issues.apache.org/jira/browse/HDFS-822?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12802835#action_12802835 ] 

Hudson commented on HDFS-822:
-----------------------------

Integrated in Hadoop-Hdfs-trunk #206 (See [http://hudson.zones.apache.org/hudson/job/Hadoop-Hdfs-trunk/206/])
    . Appends to already-finalized blocks can rename across volumes. Contributed by Hairong Kuang.


> Appends to already-finalized blocks can rename across volumes
> -------------------------------------------------------------
>
>                 Key: HDFS-822
>                 URL: https://issues.apache.org/jira/browse/HDFS-822
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>    Affects Versions: 0.21.0, 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Hairong Kuang
>            Priority: Blocker
>             Fix For: 0.21.0, 0.22.0
>
>         Attachments: HDFS-822.patch, HDFS-822.patch, HDFS-822.patch
>
>
> This is a performance thing. As I understand the code in FSDataset.append, if the block is already finalized, it needs to move it into the RBW directory so it can go back into a "being written" state. This is done using volumes.getNextVolume without preference to the volume that the block currently exists on. It seems to me that this could cause a lot of slow cross-volume copies on applications that periodically append/close/append/close a file. Instead, getNextVolume could provide an alternate form that gives preference to a particular volume, so the rename stays on the same disk.

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