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Sanjay Radia commented on HADOOP-8473: -------------------------------------- There are two separate problems here as mentioned in your description - please split into two separate jiras: * correctness - two replicas are not on the same node * performance optimization - "choose the target and source node on the same node group for balancing as the first priority". > Update Balancer to support new NetworkTopology with NodeGroup > ------------------------------------------------------------- > > Key: HADOOP-8473 > URL: https://issues.apache.org/jira/browse/HADOOP-8473 > Project: Hadoop Common > Issue Type: Sub-task > Components: util > Affects Versions: 1.0.0, 2.0.0-alpha > Reporter: Junping Du > Assignee: Junping Du > Attachments: HADOOP-8473-Balancer-NodeGroup-aware.patch > > > Since the Balancer is a Hadoop Tool, it was updated to be directly aware of > four-layer hierarchy instead of creating an alternative Balancer > implementation. To accommodate extensibility, a new protected method, > doChooseNodesForCustomFaultDomain is now called from the existing chooseNodes > method so that a subclass of the Balancer could customize the balancer > algotirhm for other failure and locality topologies. An alternative option is > to encapsulate the algorithm used for the four-layer hierarchy into a > collaborating strategy class. > The key changes introduced to support a four-layer hierarchy were to override > the algorithm of choosing <source, target> pairs for balancing. Unit tests > were created to test the new algorithm. > The algorithm now makes sure to choose the target and source node on the same > node group for balancing as the first priority. Then the overall balancing > policy is: first doing balancing between nodes within the same nodegroup then > the same rack and off rack at last. Also, we need to check no duplicated > replicas live in the same node group after balancing. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira