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Date: Mon, 19 May 2008 10:35:55 -0700 (PDT)
From: "dhruba borthakur (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3310) Lease recovery for append
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    [ https://issues.apache.org/jira/browse/HADOOP-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598011#action_12598011 ] 

dhruba borthakur commented on HADOOP-3310:
------------------------------------------

every read request has the blockid and the generation stamp. if the datanode cannot find the block (because the generation stamp has changed), then it will return an exception. 

The current code also behaves as folows: When a client gets an exception, it retries other replicas. If all these replicas fail, then it goes back to the namenode to re-retrieve block locations. Now, it should get the correct generation stamp of the block. Then, the client will retry the read request to the datanode and this one shud succeed.

do you think that this will work?

> Lease recovery for append
> -------------------------
>
>                 Key: HADOOP-3310
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3310
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: 3310_20080514.patch, 3310_20080516b.patch, 3310_20080516c.patch
>
>
> In order to support file append, a GenerationStamp is associated with each block.  Lease recovery will be performed when there is a possibility that the replicas of a block in a lease may have different GenerationStamp values.
> For more details, see the documentation in HADOOP-1700.

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