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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1846) Don't fill preallocated portion of edits log with 0x00
Date Wed, 27 Apr 2011 23:47:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1846?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13026049#comment-13026049
] 

Hadoop QA commented on HDFS-1846:
---------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12477582/hdfs-1846.1.patch
  against trunk revision 1097252.

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

    +1 tests included.  The patch appears to include 2 new or modified tests.

    +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
warnings.

    -1 core tests.  The patch failed these core unit tests:
                  org.apache.hadoop.hdfs.server.namenode.TestEditLogFileOutputStream
                  org.apache.hadoop.hdfs.TestFileConcurrentReader
                  org.apache.hadoop.hdfs.tools.offlineEditsViewer.TestOfflineEditsViewer

    +1 contrib tests.  The patch passed contrib unit tests.

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

Test results: https://builds.apache.org/hudson/job/PreCommit-HDFS-Build/421//testReport/
Findbugs warnings: https://builds.apache.org/hudson/job/PreCommit-HDFS-Build/421//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/hudson/job/PreCommit-HDFS-Build/421//console

This message is automatically generated.

> Don't fill preallocated portion of edits log with 0x00
> ------------------------------------------------------
>
>                 Key: HDFS-1846
>                 URL: https://issues.apache.org/jira/browse/HDFS-1846
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.23.0
>            Reporter: Aaron T. Myers
>            Assignee: Aaron T. Myers
>         Attachments: hdfs-1846-perf-analysis.0.patch, hdfs-1846.0.txt, hdfs-1846.1.patch
>
>
> HADOOP-2330 added a feature to preallocate space in the local file system for the NN
transaction log. That change seeks past the current end of the file and writes out some data,
which on most systems results in the intervening data in the file being filled with zeros.
Most underlying file systems have special handling for sparse files, and don't actually allocate
blocks on disk for blocks of a file which consist completely of 0x00.
> I've seen cases in the wild where the volume an edits dir is on fills up, resulting in
a partial final transaction being written out to disk. If you examine the bytes of this (now
corrupt) edits file, you'll see the partial final transaction followed by a lot of zeros,
suggesting that the preallocation previously succeeded before the volume ran out of space.
If we fill the preallocated space with something other than zeros, we'd likely see the failure
at preallocation time, rather than transaction-writing time, and so cause the NN to crash
earlier, without a partial transaction being written out.
> I also hypothesize that filling the preallocated space in the edits log with something
other than 0x00 will result in a performance improvement in NN throughput. I haven't tested
this yet, but I intend to as part of this JIRA.

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