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I managed to launch a spark application on Yarn. However memory usage is kind of weird as you can see below :
http://imgur.com/1k6VvSI
What does memory reserved mean ? How can i manage to efficiently use all the memory available ?
Thanks in advance.
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To prevent this unfortunate situation, when space on a node is offered to an application, if the application cannot immediately use it, it reserves it, and no other application can be allocated a container on that node until the reservation is fulfilled. Each node may have only one reserved container.
YARN uses the MB of memory and virtual cores per node to allocate and track resource usage. For example, a 5 node cluster with 12 GB of memory allocated per node for YARN has a total memory capacity of 60GB. For a default 2GB container size, YARN has room to allocate 30 containers of 2GB each.
You can get to it in two ways: http:/hostname:8088, where hostname is the host name of the server where Resource Manager service runs. Otherwise, from Ambari UI click on YARN (left bar) then click on Quick Links at top middle, then select Resource Manager. You will see the memory and CPU used for each container.
Check out this blog from Cloudera that explains the new memory management in YARN.
Here's the pertinent bits:
... An implementation detail of this change that prevents applications from starving under this new flexibility is the notion of reserved containers. Imagine two jobs are running that each have enough tasks to saturate more than the entire cluster. One job wants each of its mappers to get 1GB, and another job wants its mappers to get 2GB. Suppose the first job starts and fills up the entire cluster. Whenever one of its task finishes, it will leave open a 1GB slot. Even though the second job deserves the space, a naive policy will give it to the first one because it’s the only job with tasks that fit. This could cause the second job to be starved indefinitely. To prevent this unfortunate situation, when space on a node is offered to an application, if the application cannot immediately use it, it reserves it, and no other application can be allocated a container on that node until the reservation is fulfilled. Each node may have only one reserved container. The total reserved memory amount is reported in the ResourceManager UI. A high number means that it may take longer for new jobs to get space. ,,,
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A container will become reserved state when the container is assigned to some nodemanager node which do not have enough resource(cpu or memory) for it.
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