add faq for schedule

docs/faq.md

@@ -11,3 +11,12 @@ A: We recommend deploying them on the same subnet. In theory, as long as the net
 ### Q: If user find a job to retry multiple times, how to diagnose the cause?
 
 A: Users can find historical job logs through yarn. Please check [issue-1072](https://github.com/Microsoft/pai/issues/1072)'s answer.
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+### Q: To improve the cluster usage, user would like to see a VC can use up all cluster resource if others don’t use it.
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+A: OpenPAI use [capacity scheduler]((https://hadoop.apache.org/docs/r1.2.1/capacity_scheduler.html)) of YARN for resource allocation. maximum-capacity defines a limit beyond which a queue cannot use the capacity of the cluster. This provides a means to limit how much excess capacity a queue can use. By default, there is no limit. [OpenPAI capacity scheduler](../pai-management/bootstrap/hadoop-resource-manager/hadoop-resource-manager-configuration/capacity-scheduler.xml.template) not set this item and there is no limit. By default, a VC can use up all cluster resource if others don’t use it.
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+### Q: To ensure one user cannot occupy excessive resource, operator would like to set a quota constraint for individual users. 
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+A: OpenPAI use capacity scheduler of YARN for resource allocation. User can configure the item "[yarn.scheduler.capacity.root.{{ queueName }}.minimum-user-limit-percent](https://hadoop.apache.org/docs/r1.2.1/capacity_scheduler.html)" to control the user's resource quota. This configuration item is in this file [capacity-scheduler.xml.template](../pai-management/bootstrap/hadoop-resource-manager/hadoop-resource-manager-configuration/capacity-scheduler.xml.template) of OpenPAI.
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