HDFS-6920. Archival Storage: check the storage type of delNodeHintStorage when deleting a replica. Contributed by Tsz Wo Nicholas Sze.

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

@@ -2771,12 +2771,9 @@ private void chooseExcessReplicates(final Collection<DatanodeStorageInfo> nonExc
     final DatanodeStorageInfo addedNodeStorage
         = DatanodeStorageInfo.getDatanodeStorageInfo(nonExcess, addedNode);
     while (nonExcess.size() - replication > 0) {
-      // check if we can delete delNodeHint
       final DatanodeStorageInfo cur;
-      if (firstOne && delNodeHintStorage != null
-          && (moreThanOne.contains(delNodeHintStorage)
-              || (addedNodeStorage != null
-                  && !moreThanOne.contains(addedNodeStorage)))) {
+      if (useDelHint(firstOne, delNodeHintStorage, addedNodeStorage,
+          moreThanOne, excessTypes)) {
         cur = delNodeHintStorage;
       } else { // regular excessive replica removal
         cur = replicator.chooseReplicaToDelete(bc, b, replication,
@@ -2806,6 +2803,27 @@ private void chooseExcessReplicates(final Collection<DatanodeStorageInfo> nonExc
     }
   }
 
+  /** Check if we can use delHint */
+  static boolean useDelHint(boolean isFirst, DatanodeStorageInfo delHint,
+      DatanodeStorageInfo added, List<DatanodeStorageInfo> moreThan1Racks,
+      List<StorageType> excessTypes) {
+    if (!isFirst) {
+      return false; // only consider delHint for the first case
+    } else if (delHint == null) {
+      return false; // no delHint
+    } else if (!excessTypes.remove(delHint.getStorageType())) {
+      return false; // delHint storage type is not an excess type
+    } else {
+      // check if removing delHint reduces the number of racks
+      if (moreThan1Racks.contains(delHint)) {
+        return true; // delHint and some other nodes are under the same rack 
+      } else if (added != null && !moreThan1Racks.contains(added)) {
+        return true; // the added node adds a new rack
+      }
+      return false; // removing delHint reduces the number of racks;
+    }
+  }
+
   private void addToExcessReplicate(DatanodeInfo dn, Block block) {
     assert namesystem.hasWriteLock();
     LightWeightLinkedSet<Block> excessBlocks = excessReplicateMap.get(dn.getDatanodeUuid());

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

@@ -792,8 +792,15 @@ public DatanodeStorageInfo chooseReplicaToDelete(BlockCollection bc,
         minSpaceStorage = storage;
       }
     }
-    final DatanodeStorageInfo storage = oldestHeartbeatStorage != null?
-        oldestHeartbeatStorage : minSpaceStorage;
+
+    final DatanodeStorageInfo storage;
+    if (oldestHeartbeatStorage != null) {
+      storage = oldestHeartbeatStorage;
+    } else if (minSpaceStorage != null) {
+      storage = minSpaceStorage;
+    } else {
+      return null;
+    }
     excessTypes.remove(storage.getStorageType());
     return storage;
   }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestBlockManager.java

@@ -38,6 +38,7 @@
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.StorageType;
 import org.apache.hadoop.hdfs.protocol.Block;
 import org.apache.hadoop.hdfs.protocol.BlockListAsLongs;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
@@ -46,6 +47,7 @@
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeStorage;
 import org.apache.hadoop.net.NetworkTopology;
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.Mockito;
@@ -599,5 +601,19 @@ public void testSafeModeIBRAfterIncremental() throws Exception {
         new BlockListAsLongs(null, null));
     assertEquals(1, ds.getBlockReportCount());
   }
-}
 
+  @Test
+  public void testUseDelHint() {
+    DatanodeStorageInfo delHint = new DatanodeStorageInfo(
+        DFSTestUtil.getLocalDatanodeDescriptor(), new DatanodeStorage("id"));
+    List<DatanodeStorageInfo> moreThan1Racks = Arrays.asList(delHint);
+    List<StorageType> excessTypes = new ArrayList<StorageType>();
+
+    excessTypes.add(StorageType.DEFAULT);
+    Assert.assertTrue(BlockManager.useDelHint(true, delHint, null,
+        moreThan1Racks, excessTypes));
+    excessTypes.add(StorageType.SSD);
+    Assert.assertFalse(BlockManager.useDelHint(true, delHint, null,
+        moreThan1Racks, excessTypes));
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestReplicationPolicy.java

@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Matchers.any;
 import static org.mockito.Mockito.mock;
@@ -935,6 +936,12 @@ public void testChooseReplicaToDelete() throws Exception {
     assertEquals(2, first.size());
     assertEquals(2, second.size());
     List<StorageType> excessTypes = new ArrayList<StorageType>();
+    {
+      // test returning null
+      excessTypes.add(StorageType.SSD);
+      assertNull(replicator.chooseReplicaToDelete(
+          null, null, (short)3, first, second, excessTypes));
+    }
     excessTypes.add(StorageType.DEFAULT);
     DatanodeStorageInfo chosen = replicator.chooseReplicaToDelete(
         null, null, (short)3, first, second, excessTypes);
@@ -950,7 +957,7 @@ public void testChooseReplicaToDelete() throws Exception {
         null, null, (short)2, first, second, excessTypes);
     assertEquals(chosen, storages[5]);
   }
-  
+
   /**
    * This testcase tests whether the default value returned by
    * DFSUtil.getInvalidateWorkPctPerIteration() is positive,