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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1612) HDFS Design Documentation is outdated
Date Thu, 24 Feb 2011 03:44:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998686#comment-12998686

Hadoop QA commented on HDFS-1612:

-1 overall.  Here are the results of testing the latest attachment 
  against trunk revision 1072023.

    +1 @author.  The patch does not contain any @author tags.

    +0 tests included.  The patch appears to be a documentation patch that doesn't require

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit

    -1 core tests.  The patch failed these core unit tests:

    -1 contrib tests.  The patch failed contrib unit tests.

    +1 system test framework.  The patch passed system test framework compile.

Test results: https://hudson.apache.org/hudson/job/PreCommit-HDFS-Build/208//testReport/
Findbugs warnings: https://hudson.apache.org/hudson/job/PreCommit-HDFS-Build/208//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://hudson.apache.org/hudson/job/PreCommit-HDFS-Build/208//console

This message is automatically generated.

> HDFS Design Documentation is outdated
> -------------------------------------
>                 Key: HDFS-1612
>                 URL: https://issues.apache.org/jira/browse/HDFS-1612
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: documentation
>    Affects Versions: 0.20.2, 0.21.0
>         Environment: http://hadoop.apache.org/hdfs/docs/current/hdfs_design.html#The+Persistence+of+File+System+Metadata
> http://hadoop.apache.org/common/docs/r0.20.2/hdfs_design.html#The+Persistence+of+File+System+Metadata
>            Reporter: Joe Crobak
>            Priority: Minor
>         Attachments: HDFS-1612.patch
> I was trying to discover details about the Secondary NameNode, and came across the description
below in the HDFS design doc.
> {quote}
> The NameNode keeps an image of the entire file system namespace and file Blockmap in
memory. This key metadata item is designed to be compact, such that a NameNode with 4 GB of
RAM is plenty to support a huge number of files and directories. When the NameNode starts
up, it reads the FsImage and EditLog from disk, applies all the transactions from the EditLog
to the in-memory representation of the FsImage, and flushes out this new version into a new
FsImage on disk. It can then truncate the old EditLog because its transactions have been applied
to the persistent FsImage. This process is called a checkpoint. *In the current implementation,
a checkpoint only occurs when the NameNode starts up. Work is in progress to support periodic
checkpointing in the near future.*
> {quote}
> (emphasis mine).
> Note that this directly conflicts with information in the hdfs user guide, http://hadoop.apache.org/common/docs/r0.20.2/hdfs_user_guide.html#Secondary+NameNode
> and http://hadoop.apache.org/hdfs/docs/current/hdfs_user_guide.html#Checkpoint+Node
> I haven't done a thorough audit of that doc-- I only noticed the above inaccuracy.

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