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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3287) Being able to set default job configuration values on the jobtracker
Date Tue, 20 May 2008 03:20:55 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598167#action_12598167

Alejandro Abdelnur commented on HADOOP-3287:

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
> 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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