[jira] [Updated] (HDFS-4452) getAdditionalBlock() can create multiple blocks if the client times out and retries.

["Konstantin Shvachko (JIRA)" <ji...@apache.org>]

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

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

    Attachment: TestAddBlockRetry.java

Here is a simple test I used to catch the race. You just need to run it in debugger and set a breakpoint in FSNamesystem.getAdditionalBlock() on the line that calls chooseTarget().
                
> 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: 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.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira