HDFS-11370. Optimize NamenodeFsck#getReplicaInfo. Contributed Takanobu Asanuma.

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

@@ -24,7 +24,9 @@ import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.ReplicaState;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 import static org.apache.hadoop.hdfs.server.common.HdfsServerConstants.BlockUCState.COMPLETE;
 
@@ -109,6 +111,29 @@ public class BlockUnderConstructionFeature {
     return storages;
   }
 
+  /**
+   * Note that this iterator doesn't guarantee thread-safe. It depends on
+   * external mechanisms such as the FSNamesystem lock for protection.
+   */
+  public Iterator<DatanodeStorageInfo> getExpectedStorageLocationsIterator() {
+    return new Iterator<DatanodeStorageInfo>() {
+      private int index = 0;
+
+      @Override
+      public boolean hasNext() {
+        return index <  replicas.length;
+      }
+
+      @Override
+      public DatanodeStorageInfo next() {
+        if (!hasNext()) {
+          throw new NoSuchElementException();
+        }
+        return replicas[index++].getExpectedStorageLocation();
+      }
+    };
+  }
+
   /**
    * @return the index array indicating the block index in each storage. Used
    * only by striped blocks.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeFsck.java

@@ -589,23 +589,27 @@ public class NamenodeFsck implements DataEncryptionKeyFactory {
       return "";
     }
     final boolean isComplete = storedBlock.isComplete();
-    DatanodeStorageInfo[] storages = isComplete ?
-        blockManager.getStorages(storedBlock) :
-        storedBlock.getUnderConstructionFeature().getExpectedStorageLocations();
+    Iterator<DatanodeStorageInfo> storagesItr;
     StringBuilder sb = new StringBuilder(" [");
     final boolean isStriped = storedBlock.isStriped();
     Map<DatanodeStorageInfo, Long> storage2Id = new HashMap<>();
-    if (isStriped && isComplete) {
-      long blockId = storedBlock.getBlockId();
-      Iterable<StorageAndBlockIndex> sis =
-          ((BlockInfoStriped)storedBlock).getStorageAndIndexInfos();
-      for (StorageAndBlockIndex si: sis){
-        storage2Id.put(si.getStorage(), blockId + si.getBlockIndex());
+    if (isComplete) {
+      if (isStriped) {
+        long blockId = storedBlock.getBlockId();
+        Iterable<StorageAndBlockIndex> sis =
+            ((BlockInfoStriped) storedBlock).getStorageAndIndexInfos();
+        for (StorageAndBlockIndex si : sis) {
+          storage2Id.put(si.getStorage(), blockId + si.getBlockIndex());
+        }
       }
+      storagesItr = storedBlock.getStorageInfos();
+    } else {
+      storagesItr = storedBlock.getUnderConstructionFeature()
+          .getExpectedStorageLocationsIterator();
     }
 
-    for (int i = 0; i < storages.length; i++) {
-      DatanodeStorageInfo storage = storages[i];
+    while (storagesItr.hasNext()) {
+      DatanodeStorageInfo storage = storagesItr.next();
       if (isStriped && isComplete) {
         long index = storage2Id.get(storage);
         sb.append("blk_" + index + ":");
@@ -649,7 +653,7 @@ public class NamenodeFsck implements DataEncryptionKeyFactory {
           sb.append("LIVE)");
         }
       }
-      if (i < storages.length - 1) {
+      if (storagesItr.hasNext()) {
         sb.append(", ");
       }
     }