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Tom White commented on MAPREDUCE-1700: -------------------------------------- [~xumingming], the set of packages to blacklist came from the Jetty (http://docs.codehaus.org/display/JETTY/Classloading), which is why Commons Logging and Log4j were included. Excluding logging classes prevents inadvertant double initialization of the logging system - once when the task JVM starts and again when the user code is loaded. Note that you can change the system default by setting mapreduce.job.classloader.system.classes. > User supplied dependencies may conflict with MapReduce system JARs > ------------------------------------------------------------------ > > Key: MAPREDUCE-1700 > URL: https://issues.apache.org/jira/browse/MAPREDUCE-1700 > Project: Hadoop Map/Reduce > Issue Type: Bug > Components: task > Reporter: Tom White > Assignee: Tom White > Fix For: 2.0.3-alpha > > Attachments: MAPREDUCE-1700-ccl.patch, MAPREDUCE-1700-ccl.patch, > MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, > MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, > MAPREDUCE-1700.patch, MAPREDUCE-1700.patch > > > If user code has a dependency on a version of a JAR that is different to the > one that happens to be used by Hadoop, then it may not work correctly. This > happened with user code using a different version of Avro, as reported > [here|https://issues.apache.org/jira/browse/AVRO-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852081#action_12852081]. > The problem is analogous to the one that application servers have with WAR > loading. Using a specialized classloader in the Child JVM is probably the way > to solve this. -- This message was sent by Atlassian JIRA (v6.1#6144)