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Date: Fri, 23 Jan 2015 11:32:39 +0000 (UTC)
From: "Hudson (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HDFS-3519) Checkpoint upload may interfere with
 a concurrent saveNamespace
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    [ https://issues.apache.org/jira/browse/HDFS-3519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14289108#comment-14289108 ] 

Hudson commented on HDFS-3519:
------------------------------

FAILURE: Integrated in Hadoop-Yarn-trunk #816 (See [https://builds.apache.org/job/Hadoop-Yarn-trunk/816/])
HDFS-3519. Checkpoint upload may interfere with a concurrent saveNamespace. Contributed by Ming Ma. (cnauroth: rev d3268c4b10a0f728b554ddb6d69b666a9ca13f12)
* hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
* hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ImageServlet.java
* hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestStandbyCheckpoints.java
* hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java


> Checkpoint upload may interfere with a concurrent saveNamespace
> ---------------------------------------------------------------
>
>                 Key: HDFS-3519
>                 URL: https://issues.apache.org/jira/browse/HDFS-3519
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: Todd Lipcon
>            Assignee: Ming Ma
>            Priority: Critical
>             Fix For: 2.7.0
>
>         Attachments: HDFS-3519-2.patch, HDFS-3519-3.patch, HDFS-3519-branch-2.patch, HDFS-3519.patch, test-output.txt
>
>
> TestStandbyCheckpoints failed in [precommit build 2620|https://builds.apache.org/job/PreCommit-HDFS-Build/2620//testReport/] due to the following issue:
> - both nodes were in Standby state, and configured to checkpoint "as fast as possible"
> - NN1 starts to save its own namespace
> - NN2 starts to upload a checkpoint for the same txid. So, both threads are writing to the same file fsimage.ckpt_12, but the actual file contents correspond to the uploading thread's data.
> - NN1 finished its saveNamespace operation while NN2 was still uploading. So, it renamed the ckpt file. However, the contents of the file are still empty since NN2 hasn't sent any bytes
> - NN2 finishes the upload, and the rename() call fails, which causes the directory to be marked failed, etc.
> The result is that there is a file fsimage_12 which appears to be a finalized image but in fact is incompletely transferred. When the transfer completes, the problem "heals itself" so there wouldn't be persistent corruption unless the machine crashes at the same time. And even then, we'd still have the earlier checkpoint to restore from.
> This same race could occur in a non-HA setup if a user puts the NN in safe mode and issues saveNamespace operations concurrent with a 2NN checkpointing, I believe.


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