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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5369) Small tweaks to reduce MapFile index size
Date Tue, 10 Mar 2009 13:28:51 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5369?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12680459#action_12680459
] 

Hadoop QA commented on HADOOP-5369:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12401772/smaller_mapfile.patch
  against trunk revision 751994.

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

    +1 tests included.  The patch appears to include 3 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 warnings.

    +1 Eclipse classpath. The patch retains Eclipse classpath integrity.

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

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

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

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-minerva.apache.org/42/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-minerva.apache.org/42/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-minerva.apache.org/42/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-minerva.apache.org/42/console

This message is automatically generated.

> Small tweaks to reduce MapFile index size
> -----------------------------------------
>
>                 Key: HADOOP-5369
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5369
>             Project: Hadoop Core
>          Issue Type: Improvement
>            Reporter: Ben Maurer
>            Assignee: Ben Maurer
>             Fix For: 0.21.0
>
>         Attachments: mapfile.patch, smaller_mapfile.patch, smaller_mapfile.patch, smaller_mapfile.patch,
smaller_mapfile.patch
>
>
> Two minor tweaks can help reduce the memory overhead of the MapFile index a bit:
> 1) Because the index file is a sequence file, it's length is not known. That means the
index is built using the standard "mulitply the size of the buffer on overflow" with a factor
of 3/2. With small keys, the slack in the index can be substantial. This patch has a constant
upper bound on the amount of slack allowed.
> 2) In block compressed map files the index file often has entries with the same offset
(because the compressed block had more than index interval keys). The entries with identical
offsets do not help MapFile do random access any faster. This patch eliminates these types
of entries from new map files, and ignores them while reading old map files. This patch greatly
helped with memory usage on a compressed hbase table.

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