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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-4452) getAdditionalBlock() can create multiple blocks if the client times out and retries.
Date Fri, 01 Feb 2013 05:39:16 GMT

     [ https://issues.apache.org/jira/browse/HDFS-4452?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Konstantin Shvachko updated HDFS-4452:
--------------------------------------

    Status: Patch Available  (was: Open)

I tested it locally. It passes all tests including TestDFSClientRetries, which models the
case when the retry happens after the first attempt completes getAdditionalBlock() fully.
I'll write another test which models simultaneous execution of  getAdditionalBlock() by two
threads shortly.
                
> getAdditionalBlock() can create multiple blocks if the client times out and retries.
> ------------------------------------------------------------------------------------
>
>                 Key: HDFS-4452
>                 URL: https://issues.apache.org/jira/browse/HDFS-4452
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.2-alpha
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>            Priority: Critical
>         Attachments: getAdditionalBlock.patch, TestAddBlockRetry.java
>
>
> HDFS client tries to addBlock() to a file. If NameNode is busy the client can timeout
and will reissue the same request again. The two requests will race with each other in {{FSNamesystem.getAdditionalBlock()}},
which can result in creating two new blocks on the NameNode while the client will know of
only one of them. This eventually results in {{NotReplicatedYetException}} because the extra
block is never reported by any DataNode, which stalls file creation and puts it in invalid
state with an empty block in the middle.

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