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https://issues.apache.org/jira/browse/YARN-1228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13775769#comment-13775769
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Sandy Ryza commented on YARN-1228:
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Existing tests verify that absolute paths and not giving any file work. Adding
a file to the classpath at runtime is difficult, so I verified that it picks up
files from the classpath by manually testing on a pseudo-distributed cluster.
> Clean up Fair Scheduler configuration loading
> ---------------------------------------------
>
> Key: YARN-1228
> URL: https://issues.apache.org/jira/browse/YARN-1228
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: scheduler
> Affects Versions: 2.1.1-beta
> Reporter: Sandy Ryza
> Assignee: Sandy Ryza
> Attachments: YARN-1228.patch
>
>
> Currently the Fair Scheduler is configured in two ways
> * An allocations file that has a different format than the standard Hadoop
> configuration file, which makes it easier to specify hierarchical objects
> like queues and their properties.
> * With properties like yarn.scheduler.fair.max.assign that are specified in
> the standard Hadoop configuration format.
> The standard and default way of configuring it is to use fair-scheduler.xml
> as the allocations file and to put the yarn.scheduler properties in
> yarn-site.xml.
> It is also possible to specify a different file as the allocations file, and
> to place the yarn.scheduler properties in fair-scheduler.xml, which will be
> interpreted as in the standard Hadoop configuration format. This flexibility
> is both confusing and unnecessary.
> Additionally, the allocation file is loaded as fair-scheduler.xml from the
> classpath if it is not specified, but is loaded as a File if it is. This
> causes two problems
> 1. We see different behavior when not setting the
> yarn.scheduler.fair.allocation.file, and setting it to fair-scheduler.xml,
> which is its default.
> 2. Classloaders may choose to cache resources, which can break the reload
> logic when yarn.scheduler.fair.allocation.file is not specified.
> We should never allow the yarn.scheduler properties to go into
> fair-scheduler.xml. And we should always load the allocations file as a
> file, not as a resource on the classpath. To preserve existing behavior and
> allow loading files from the classpath, we can look for files on the
> classpath, but strip of their scheme and interpret them as Files.
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