Set Application Limits

To avoid system-thrash due to an unmanageable load -- caused either by malicious users, or by accident -- the Capacity Scheduler enables you to place a static, configurable limit on the total number of concurrently active (both running and pending) applications at any one time.

You can set the maximum applications limit using the maximum-applications configuration property. The default value is 10,000.

In Cloudera Manager, select the YARN service.
Click the Configuration tab.
Search for scheduler.
In Capacity Scheduler Configuration Advanced Configuration Snippet (Safety Valve)add the following:
```
Name: yarn.scheduler.capacity.maximum-applications
Value: 10000
```
The limit for running applications in any specific queue is a fraction of this total limit, proportional to its capacity. This is a hard limit, which means that once this limit is reached for a queue, any new applications to that queue will be rejected, and clients will have to wait and retry later. This limit can be explicitly overridden on a per-queue basis with the following configuration property:
```
Name: yarn.scheduler.capacity.<queue-path>.maximum-applications
Value: absolute-capacity * yarn.scheduler.capacity.maximum-applications
```
There is another resource limit that can be used to set a maximum percentage of cluster resources allocated specifically to ApplicationMasters. The maximum-am-resource-percent property has a default value of 10%, and exists to avoid cross-application deadlocks where significant resources in the cluster are occupied entirely by the Containers running ApplicationMasters. This property also indirectly controls the number of concurrent running applications in the cluster, with each queue limited to a number of running applications proportional to its capacity.
```
Name: yarn.scheduler.capacity.maximum-am-resource-percent
Value: 0.1
```
As with maximum-applications, this limit can also be overridden on a per-queue basis:
```
Name:  yarn.scheduler.capacity.<queue-path>.maximum-am-resource-percent
Value: 0.1
```
All of these limits ensure that no single application, user, or queue can cause catastrophic failure, or monopolize the cluster and cause excessive degradation of cluster performance.