[HDFS-16439] Makes calculating maxNodesPerRack simpler

• Type: Improvement
• Status: In Progress
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.4.0
• Component/s: namenode
• Labels: pull-request-available
• Assignee: JiangHua Zhu
• Reporter: JiangHua Zhu
• Created: 26/Jan/22 10:00
• Updated: 27/Jan/22 14:32

Description

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).

Issue Links

• links to: GitHub Pull Request #3937