The YARN Service (MapReduce v2)
The YARN service is only available with CDH4.
The current upstream MRv2 release is not yet stable, and should not be considered production-ready at this time. It is given by default a lower alternatives priority than MRv1.
By default, the original MapReduce (MRv1) is set to a higher alternatives priority than YARN. Therefore, even though you add and start the YARN service, MapReduce jobs will still be run under MRv1. If you want to use YARN to run jobs, you will need to change its alternatives priority to be higher than MRv1.
To add the YARN service and configure it to have a higher priority than MRv1, do the following:
- Click the Services tab, then choose All Services.
- From the Actions menu, select Add a Service. A list of possible services are displayed. You can add one type of service at a time.
- Follow the instructions in the Add Service wizard to add the service.
- Stop the YARN service.
- Go to the YARN service page (by selecting the YARN service from the Services menu or from the All Services page).
- Go to the Configuration tab, and search for "Alternatives Priority".
- Change the priority value to be higher than MRv1. (MRv1 by default is set to 92.) Alternatively, you can lower the MapReduce service alternatives priority, via the Configuration tab for the MapReduce service.)
- Save your configuration change.
- Start the YARN service.
- Redeploy the client configuration to have the changes take effect; (from the YARN Status page, Actions menu, click Deploy Client Configuration).
Creating the Job History Directory
When adding the YARN service, the Add Service wizard automatically creates a job history directory for HBase. If you quit the Add Service wizard or it does not finish, you can create the directory outside the wizard by doing these steps:
- Choose Create Job History Dir from the Actions menu in the YARN > Status tab.
- Click Create Job History Dir again to confirm.
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