The tuning of this property totally depends on your use case.   yarn.scheduler.capacity.<queue-path>.maximum-am-resource-percent: Queue level AMshare For instance lets say your cluster is primarily used for oozie. For each oozie action [except sshaction] you will have a oozie launcher application(map-only job which will start the jobs) and an external application which actually does the job. In this case you will have a requirement to run lots of application and inturn lots of application master. In such cases if you want to achieve more parallelism you will create a dedicated queue for launcher application[oozie.launcher.mapred.job.queue.name can be used to direct all launcher application to this dedicated queue] and another another queue for the external application. You can then set 0.5 to launcher queue which has a single AM and single Mapper so equal distribution is rational setting.   At cluster level yarn.scheduler.capacity.maximum-am-resource-percent - lets say you have the capacity to run 1000 containers and each of your application on an average runs 10 mapper. Then setting this value to 10% would allow you to run, 100 application in parallel (100 application master and 900 mappers). If you set this to 20% then you get a chance to run 200 application in parallel (200 application master and 800 mapper container) - each application will run short of 2 containers and will wait for other application to finish and the average throughput of your application will be little longer.  ... View more

yes you have to upgrade to cdh6.1.0 or higher to use impala-3.1.0 - Its not possible to selectively upgrade impala alone   https://www.cloudera.com/documentation/enterprise/6/release-notes/topics/rg_cdh_61_packaging.html     ... View more

Impala relies on hivemetastore for persisting table metadata. HMS inturn uses db to persist metadata. So if the db's filesystem is out of space, request from hms to persist metadata will be denied and yes if the space on the db is not freed up then request from hms will be failed and eventually impala also fails the query ... View more