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https://issues.apache.org/jira/browse/MAPREDUCE-6237?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14301876#comment-14301876
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Hadoop QA commented on MAPREDUCE-6237:
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{color:red}-1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12695991/mapreduce-6237.patch
against trunk revision 1c09ca2.
{color:green}+1 @author{color}. The patch does not contain any @author
tags.
{color:green}+1 tests included{color}. The patch appears to include 1 new
or modified test files.
{color:green}+1 javac{color}. The applied patch does not increase the
total number of javac compiler warnings.
{color:green}+1 javadoc{color}. There were no new javadoc warning messages.
{color:green}+1 eclipse:eclipse{color}. The patch built with
eclipse:eclipse.
{color:red}-1 findbugs{color}. The patch appears to introduce 13 new
Findbugs (version 2.0.3) warnings.
{color:green}+1 release audit{color}. The applied patch does not increase
the total number of release audit warnings.
{color:green}+1 core tests{color}. The patch passed unit tests in
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core.
Test results:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5140//testReport/
Findbugs warnings:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5140//artifact/patchprocess/newPatchFindbugsWarningshadoop-mapreduce-client-core.html
Console output:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5140//console
This message is automatically generated.
> DBRecordReader is not thread safe
> ---------------------------------
>
> Key: MAPREDUCE-6237
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6237
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 2.5.0
> Reporter: Kannan Rajah
> Assignee: Kannan Rajah
> Attachments: mapreduce-6237.patch
>
>
> DBInputFormat.createDBRecorder is reusing JDBC connections across instances
> of DBRecordReader. This is not a good idea. We should be creating separate
> connection. If performance is a concern, then we should be using connection
> pooling instead.
> I looked at DBOutputFormat.getRecordReader. It actually creates a new
> Connection object for each DBRecordReader. So can we just change
> DBInputFormat to create new Connection every time? The connection reuse code
> was added as part of connection leak bug in MAPREDUCE-1443. Any reason for
> caching the connection?
> We observed this issue in a customer setup where they were reading data from
> MySQL using Pig. As per customer, the query is returning two records which
> causes Pig to create two instances of DBRecordReader. These two instances are
> sharing the database connection instance. The first DBRecordReader runs to
> extract the first record from MySQL just fine, but then closes the shared
> connection instance. When the second DBRecordReader runs, it tries to execute
> a query to retrieve the second record on the closed shared connection
> instance, which fail. If we set
> mapred.map.tasks to 1, the query will be successful.
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