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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3521) Allow namenode to tolerate edit log corruption
Date Wed, 13 Jun 2012 17:01:44 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13294557#comment-13294557
] 

Colin Patrick McCabe commented on HDFS-3521:
--------------------------------------------

bq. cmccabe: ... you will never encounter a partial write more than 1MB from the end of the
file.

bq. szetswo: The edit log may be corrupted.

If the edit log is corrupted, we *never* want to ignore the corruption.  

UNCHECKED_REGION_LENGTH was never about ignoring corruption in general.  It was about ignoring
sentinel bytes followed by non-sentinel data.

I think we need to revert this and have a longer discussion about this.  I'm really scared
by what this change could do.  I know for sure that it breaks recovery mode, and it also appears
to degrade edit log integrity too.
                
> Allow namenode to tolerate edit log corruption
> ----------------------------------------------
>
>                 Key: HDFS-3521
>                 URL: https://issues.apache.org/jira/browse/HDFS-3521
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>             Fix For: 1.2.0
>
>         Attachments: h3521_20120610_b-1.patch, h3521_20120611_b-1.0.patch, h3521_20120611_b-1.patch
>
>
> HDFS-3479 adds checking for edit log corruption. It uses a fixed UNCHECKED_REGION_LENGTH
(=PREALLOCATION_LENGTH) so that the bytes at the end within the length is not checked.  Instead
of not checking the bytes, we should check everything and allow toleration.

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