[GitHub] [hadoop] whbing commented on a diff in pull request #5759: HDFS-17052. Improve BlockPlacementPolicyRackFaultTolerant to avoid choose nodes failed when no enough Rack.

["whbing (via GitHub)" <gi...@apache.org>]

whbing commented on code in PR #5759:
URL: https://github.com/apache/hadoop/pull/5759#discussion_r1247501492


##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyRackFaultTolerant.java:
##########
@@ -192,11 +192,23 @@ private void chooseEvenlyFromRemainingRacks(Node writer,
       } finally {
         excludedNodes.addAll(newExcludeNodes);
       }
+      if (numResultsOflastChoose == results.size()) {
+        Map<String, Integer> nodesPerRack = new HashMap<>();
+        for (DatanodeStorageInfo dsInfo : results) {
+          String rackName = dsInfo.getDatanodeDescriptor().getNetworkLocation();
+          nodesPerRack.merge(rackName, 1, Integer::sum);
+        }
+        for (int numNodes : nodesPerRack.values()) {
+          if (numNodes > bestEffortMaxNodesPerRack) {
+            bestEffortMaxNodesPerRack = numNodes;
+          }

Review Comment:
   Line 201~203 get max value, maybe we can use the following code to make it more clear and concise.
   ```java
           bestEffortMaxNodesPerRack =
               Math.max(bestEffortMaxNodesPerRack, Collections.max(nodesPerRack.values()));
   ```



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