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https://issues.apache.org/jira/browse/HADOOP-4522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12647910#action_12647910
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Matei Zaharia commented on HADOOP-4522:
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One other difference between the config in the fair scheduler and the capacity
scheduler is that the fair scheduler uses a file different than the Hadoop
config file (hadoop-site.xml/hadoop-default.xml), which actually has its own
XML format. This means that admins don't have to worry about which parts of
hadoop-site.xml they've changed and which they haven't if they want to change
the scheduling config. In my opinion it's far easier to understand the system
if hadoop-site.xml is read only on startup, rather than having to learn and
worry about which parameters get reloaded and which ones don't. Admins may also
edit a config file while the system is running in order to plan for the next
restart, and reloading some parameters may be confusing. When job persistence
is in, there won't even be too much of a cost to restarting the JobTracker -
jobs won't be lost, and the restart is very fast anyway.
By the way a note on what to do if the JT machine fails: why not use DNS and
assign the same name to a different machine? This seems a lot less complex.
> Capacity Scheduler needs to re-read its configuration
> -----------------------------------------------------
>
> Key: HADOOP-4522
> URL: https://issues.apache.org/jira/browse/HADOOP-4522
> Project: Hadoop Core
> Issue Type: New Feature
> Reporter: Vivek Ratan
>
> An external application (an Ops script, or some CLI-based tool) can change
> the configuration of the Capacity Scheduler (change the capacities of various
> queues, for example) by updating its config file. This application then needs
> to tell the Capacity Scheduler that its config has changed, which causes the
> Scheduler to re-read its configuration. It's possible that the Capacity
> Scheduler may need to interact with external applications in other similar
> ways.
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