HDFS-8073. Split BlockPlacementPolicyDefault.chooseTarget(..) so it can be easily overrided. (Contributed by Walter Su)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -385,6 +385,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8079. Move dfs.client.retry.* confs from DFSConfigKeys to
     HdfsClientConfigKeys.Retry.  (szetszwo)
 
+    HDFS-8073. Split BlockPlacementPolicyDefault.chooseTarget(..) so it
+    can be easily overrided. (Walter Su via vinayakumarb)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java

@@ -333,41 +333,8 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
             + " unavailableStorages=" + unavailableStorages
             + ", storagePolicy=" + storagePolicy);
       }
-
-      if (numOfResults == 0) {
-        writer = chooseLocalStorage(writer, excludedNodes, blocksize,
-            maxNodesPerRack, results, avoidStaleNodes, storageTypes, true)
-                .getDatanodeDescriptor();
-        if (--numOfReplicas == 0) {
-          return writer;
-        }
-      }
-      final DatanodeDescriptor dn0 = results.get(0).getDatanodeDescriptor();
-      if (numOfResults <= 1) {
-        chooseRemoteRack(1, dn0, excludedNodes, blocksize, maxNodesPerRack,
-            results, avoidStaleNodes, storageTypes);
-        if (--numOfReplicas == 0) {
-          return writer;
-        }
-      }
-      if (numOfResults <= 2) {
-        final DatanodeDescriptor dn1 = results.get(1).getDatanodeDescriptor();
-        if (clusterMap.isOnSameRack(dn0, dn1)) {
-          chooseRemoteRack(1, dn0, excludedNodes, blocksize, maxNodesPerRack,
-              results, avoidStaleNodes, storageTypes);
-        } else if (newBlock){
-          chooseLocalRack(dn1, excludedNodes, blocksize, maxNodesPerRack,
-              results, avoidStaleNodes, storageTypes);
-        } else {
-          chooseLocalRack(writer, excludedNodes, blocksize, maxNodesPerRack,
-              results, avoidStaleNodes, storageTypes);
-        }
-        if (--numOfReplicas == 0) {
-          return writer;
-        }
-      }
-      chooseRandom(numOfReplicas, NodeBase.ROOT, excludedNodes, blocksize,
-          maxNodesPerRack, results, avoidStaleNodes, storageTypes);
+      writer = chooseTargetInOrder(numOfReplicas, writer, excludedNodes, blocksize,
+          maxNodesPerRack, results, avoidStaleNodes, newBlock, storageTypes);
     } catch (NotEnoughReplicasException e) {
       final String message = "Failed to place enough replicas, still in need of "
           + (totalReplicasExpected - results.size()) + " to reach "
@@ -422,7 +389,55 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
     }
     return writer;
   }
-    
+
+  protected Node chooseTargetInOrder(int numOfReplicas, 
+                                 Node writer,
+                                 final Set<Node> excludedNodes,
+                                 final long blocksize,
+                                 final int maxNodesPerRack,
+                                 final List<DatanodeStorageInfo> results,
+                                 final boolean avoidStaleNodes,
+                                 final boolean newBlock,
+                                 EnumMap<StorageType, Integer> storageTypes)
+                                 throws NotEnoughReplicasException {
+    final int numOfResults = results.size();
+    if (numOfResults == 0) {
+      writer = chooseLocalStorage(writer, excludedNodes, blocksize,
+          maxNodesPerRack, results, avoidStaleNodes, storageTypes, true)
+          .getDatanodeDescriptor();
+      if (--numOfReplicas == 0) {
+        return writer;
+      }
+    }
+    final DatanodeDescriptor dn0 = results.get(0).getDatanodeDescriptor();
+    if (numOfResults <= 1) {
+      chooseRemoteRack(1, dn0, excludedNodes, blocksize, maxNodesPerRack,
+          results, avoidStaleNodes, storageTypes);
+      if (--numOfReplicas == 0) {
+        return writer;
+      }
+    }
+    if (numOfResults <= 2) {
+      final DatanodeDescriptor dn1 = results.get(1).getDatanodeDescriptor();
+      if (clusterMap.isOnSameRack(dn0, dn1)) {
+        chooseRemoteRack(1, dn0, excludedNodes, blocksize, maxNodesPerRack,
+            results, avoidStaleNodes, storageTypes);
+      } else if (newBlock){
+        chooseLocalRack(dn1, excludedNodes, blocksize, maxNodesPerRack,
+            results, avoidStaleNodes, storageTypes);
+      } else {
+        chooseLocalRack(writer, excludedNodes, blocksize, maxNodesPerRack,
+            results, avoidStaleNodes, storageTypes);
+      }
+      if (--numOfReplicas == 0) {
+        return writer;
+      }
+    }
+    chooseRandom(numOfReplicas, NodeBase.ROOT, excludedNodes, blocksize,
+        maxNodesPerRack, results, avoidStaleNodes, storageTypes);
+    return writer;
+  }
+  
   /**
    * Choose <i>localMachine</i> as the target.
    * if <i>localMachine</i> is not available,