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https://issues.apache.org/jira/browse/AVRO-1103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396209#comment-13396209
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Doug Cutting commented on AVRO-1103:
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(I'm mostly offline this week, so will be slow to respond.)
> your patched AvroSerialization whilst it uses the config object is still
> trying to use the parent ClassLoader so cannot find my Avro class
I'm confused by this. Using the classloader from the configuration is what
Hadoop does for Writables, no? If the configuration has the wrong classloader
then we might set that to be the same as what Class.forName() uses. Calling
Class.forName(x).getClassloader() seems circular to me.
> it would help me immensely if a version of avro-mapred 1.7 for Hadoop 2 could
> be made available
Are code changes required or simply changes in pom.xml dependencies?
> New AvroDeserializer should Locate Appropriate Classloader
> ----------------------------------------------------------
>
> Key: AVRO-1103
> URL: https://issues.apache.org/jira/browse/AVRO-1103
> Project: Avro
> Issue Type: Improvement
> Components: java
> Affects Versions: 1.7.0
> Environment: Hadoop 0.23.1 with Avro jars replaced by 1.7 jars
> Specific data classes assembled into JAR with mapper/reducer
> Reporter: Jacob Metcalf
> Assignee: Doug Cutting
> Fix For: 1.7.1
>
> Attachments: AVRO-1103-for 0.23.1.patch, AVRO-1103.patch,
> AVRO-1103.patch, AVRO-1103.patch
>
>
> Continuing on from AVRO-873 I believe some more work needs to be done to get
> the MapReduce 2 APIs in Avro 1.7 working with Hadoop 0.23. Since it revolves
> around classloaders it is complex to present a unit test which fails so I
> will explain the problem:
> - By default SpecificDatumReader will use the classloader it was loaded from
> to find a Specific class to deserialize into.
> - In earlier versions of Hadoop e.g. 0.20.2 Avro was not included so
> typically you would bundle Avro into your job jar along with the Specific
> classes so they would be on the same classpath.
>
> - However later versions of Hadoop such as 0.23 ship with Avro. Thus you find
> that the SpecificData.class.getClassloader() is typically a parent loader
> which just contains Hadoop components.
> - Thus when SpecificData goes to construct a Specific class from the schema
> it cannot locate it and silently defaults to creating a GenericData.
> In AVRO-873 an additional constructor was added to SpecificData to force it
> to use a different classloader. Thus to extend this fix to the new MR2 APIs:
> - AvroDeserializer could attempt to instantiate the class using
> Class.forName() and from this get the appropriate Classloader and pass this
> into the constructor of SpecificDatumReader.
> - Line 2771 of SpecificData.java is:
> bq. Class c = SpecificData.get().getClass(schema);
> - This would need to be changed to:
> bq. Class c = this.getClass(schema);
> I have raised this in the mail groups here:
> http://search-hadoop.com/m/wVUf1aLCwd/classloader/v=threaded so apologies if
> this is already being thought about.
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