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Date: Mon, 15 Dec 2008 11:47:44 -0800 (PST)
From: "Raghu Angadi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4865) Trigger block scans for datanode
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    [ https://issues.apache.org/jira/browse/HADOOP-4865?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12656723#action_12656723 ] 

Raghu Angadi commented on HADOOP-4865:
--------------------------------------

Mostly looks good. A few comments :

DNA_SCAN meant for NameNode to inform datanode is not used here, thus better to be removed in this patch. Even if we want such a functionality, it might be add such a method to 'DataNode Client protocol'.

I think we should remove synchronized just around manualScanList. it does not improve anything and usually synchronizing around each member separately only leads to confusion. In general it is better to keep synchronization consistent with the code around while adding a patch.

Also, I would just make 'verifyFirstBlock()' to look at the manual list first. 


> Trigger block scans for datanode
> --------------------------------
>
>                 Key: HADOOP-4865
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4865
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Brian Bockelman
>         Attachments: manual_block_scan.patch
>
>
> Provide a mechanism to trigger block scans in a datanode upon request.  Support interfaces for commands sent by the namenode and through the HTTP interface.

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