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https://issues.apache.org/jira/browse/HADOOP-3287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598167#action_12598167
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Alejandro Abdelnur commented on HADOOP-3287:
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Having an heterogeneous network would not be affected by the proposed solution.
The TT configuration is not affected by this. The proposed solution is only
about what configuration properties are sent by a client when submitting a job,
instead sending all, just to send what has been explicitly set and the rest to
be resolved using the default values set in the JT.
> Being able to set default job configuration values on the jobtracker
> --------------------------------------------------------------------
>
> Key: HADOOP-3287
> URL: https://issues.apache.org/jira/browse/HADOOP-3287
> Project: Hadoop Core
> Issue Type: Bug
> Components: conf, mapred
> Environment: all
> Reporter: Alejandro Abdelnur
> Priority: Critical
>
> The jobtracker hadoop-site.xml carries custom configuration for the cluster
> and the 'final' flag allows to fix a value ignoring any override by a client
> when submitting a job.
> There are several properties for which a cluster may want to set some default
> values (different from the ones in the hadoop-default.xml), for example:
> * enabling/disabling compression
> * type of compression, record/block
> * number of task retries
> * block replication factor
> * job priority
> * tasks JVM options
> The cluster default values should apply to submitted jobs when the job
> submitter does not care about those values. When the job submitter cares, it
> should include its preferred values. Using the final flag on the jobtracker
> hadoop-site.xml will lock the value ignoring the value set in the client
> jobconf.
> Currently the only way of doing this is to distribute the jobtracker
> hadoop-site.xml to all clients and make sure they use it when creating the
> job configuration.
> There are situations where this is not practical:
> * In a shared cluster with several clients submitting jobs. It requires
> redistributing the hadoop-site.xml to all clients.
> * In a cluster where the jobs are dispatched by a webapp application. It
> requires rebundling and redeploying the webapp.
> The current behavior happens because the jobconf when serialized, to be sent
> to the jobtracker, sends all the values found in the hadoop-default.xml
> bundled with the hadoop JAR file. On the jobtracker side, all those values
> override all but the 'final' properties of the jobtracker hadoop-site.xml.
> According to the javadocs of the Configuration.write(OutpuStream) this should
> not happen ' Writes non-default properties in this configuration.'
> If taken the javadocs as the proper behavior this is a bug in the current
> implementation and it could be easily fixed by avoiding writing default
> values on write.
> This is a generalization of the problem mentioned in Hadoop-3171.
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