[jira] [Assigned] (HDFS-16439) Makes calculating maxNodesPerRack simpler

["JiangHua Zhu (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-16439?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

JiangHua Zhu reassigned HDFS-16439:
-----------------------------------

    Assignee: JiangHua Zhu

> Makes calculating maxNodesPerRack simpler
> -----------------------------------------
>
>                 Key: HDFS-16439
>                 URL: https://issues.apache.org/jira/browse/HDFS-16439
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.4.0
>            Reporter: JiangHua Zhu
>            Assignee: JiangHua Zhu
>            Priority: Major
>
> When creating a new file, it is usually necessary to communicate with the namenode first to obtain the location of some DataNodes as the target location of Blockd. At this time, when BlockPlacementPolicyDefault#getMaxNodesPerRack() is executed, if the number of replicas is very large, once it exceeds the number of all nodes in the cluster. The following piece of code will be executed:
>        int clusterSize = clusterMap.getNumOfLeaves();
>        int totalNumOfReplicas = numOfChosen + numOfReplicas;
> if (totalNumOfReplicas > clusterSize) {
>        numOfReplicas -= (totalNumOfReplicas-clusterSize);
>        totalNumOfReplicas = clusterSize;
>      }
> Here, the calculation for numOfReplicas gets a little more complicated. It can be simplified like:
> numOfReplicas = clusterSize - numOfChosen
> It would be more helpful to understand it this way, while also freeing up a little cpu (though not a lot).



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