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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4423) Checkpoint exception causes fatal damage to fsimage.
Date Wed, 30 Jan 2013 02:41:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4423?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13566095#comment-13566095
] 

Tsz Wo (Nicholas), SZE commented on HDFS-4423:
----------------------------------------------

I have run the tests with the patch.  All tests passed except TestNetUtils but it was due
to my local network environment but not related to the patch.
                
> Checkpoint exception causes fatal damage to fsimage.
> ----------------------------------------------------
>
>                 Key: HDFS-4423
>                 URL: https://issues.apache.org/jira/browse/HDFS-4423
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 1.0.4, 1.1.1
>         Environment: CentOS 6.2
>            Reporter: ChenFolin
>            Assignee: Chris Nauroth
>            Priority: Blocker
>         Attachments: HDFS-4423-branch-1.1.patch
>
>   Original Estimate: 72h
>  Remaining Estimate: 72h
>
> The impact of class is org.apache.hadoop.hdfs.server.namenode.FSImage.java
> {code}
> boolean loadFSImage(MetaRecoveryContext recovery) throws IOException {
> ...
> latestNameSD.read();
>     needToSave |= loadFSImage(getImageFile(latestNameSD, NameNodeFile.IMAGE));
>     LOG.info("Image file of size " + imageSize + " loaded in " 
>         + (FSNamesystem.now() - startTime)/1000 + " seconds.");
>     
>     // Load latest edits
>     if (latestNameCheckpointTime > latestEditsCheckpointTime)
>       // the image is already current, discard edits
>       needToSave |= true;
>     else // latestNameCheckpointTime == latestEditsCheckpointTime
>       needToSave |= (loadFSEdits(latestEditsSD, recovery) > 0);
>     
>     return needToSave;
>   }
> {code}
> If it is the normal flow of the checkpoint,the value of latestNameCheckpointTime  is
equal to the value of latestEditsCheckpointTime,and it will exec “else”.
> The problem is that,latestNameCheckpointTime > latestEditsCheckpointTime:
> SecondNameNode starts checkpoint,
> ...
> NameNode:rollFSImage,NameNode shutdown after write latestNameCheckpointTime and before
write latestEditsCheckpointTime.
> Start NameNode:because latestNameCheckpointTime > latestEditsCheckpointTime,so
the value of needToSave is true, and it will not update “rootDir”'s nsCount that is
the cluster's file number(update exec at loadFSEdits “FSNamesystem.getFSNamesystem().dir.updateCountForINodeWithQuota()”),and
then “saveNamespace” will write file number to fsimage whit default value “1”。
> The next time,loadFSImage will fail.
> Maybe,it will work:
> {code}
> boolean loadFSImage(MetaRecoveryContext recovery) throws IOException {
> ...
> latestNameSD.read();
>     needToSave |= loadFSImage(getImageFile(latestNameSD, NameNodeFile.IMAGE));
>     LOG.info("Image file of size " + imageSize + " loaded in " 
>         + (FSNamesystem.now() - startTime)/1000 + " seconds.");
>     
>     // Load latest edits
>     if (latestNameCheckpointTime > latestEditsCheckpointTime){
>       // the image is already current, discard edits
>       needToSave |= true;
>       FSNamesystem.getFSNamesystem().dir.updateCountForINodeWithQuota();
>     }
>     else // latestNameCheckpointTime == latestEditsCheckpointTime
>       needToSave |= (loadFSEdits(latestEditsSD, recovery) > 0);
>     
>     return needToSave;
>   }
> {code}

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