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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5967) Sqoop should only use a single map task
Date Sat, 06 Jun 2009 10:50:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12716864#action_12716864

Hadoop QA commented on HADOOP-5967:

-1 overall.  Here are the results of testing the latest attachment 
  against trunk revision 782083.

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

    -1 tests included.  The patch doesn't appear to include any new or modified tests.
                        Please justify why no tests are needed for this patch.

    +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

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

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

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/472/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/472/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/472/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/472/console

This message is automatically generated.

> Sqoop should only use a single map task
> ---------------------------------------
>                 Key: HADOOP-5967
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5967
>             Project: Hadoop Core
>          Issue Type: Improvement
>            Reporter: Aaron Kimball
>            Assignee: Aaron Kimball
>            Priority: Minor
>         Attachments: single-mapper.patch
> The current DBInputFormat implementation uses SELECT ... LIMIT ... OFFSET statements
to read from a database table. This actually results in several queries all accessing the
same table at the same time. Most database implementations will actually use a full table
scan for each such query, starting at row 1 and scanning down until the OFFSET is reached
before emitting data to the client. The upshot of this is that we see O(n^2) performance in
the size of the table when using a large number of mappers, when a single mapper would read
through the table in O(n) time in the number of rows.
> This patch sets the number of map tasks to 1 in the MapReduce job sqoop launches.

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