HDFS-16076. Avoid using slow DataNodes for reading by sorting locations (#3117)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -516,6 +516,10 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   // Whether to enable datanode's stale state detection and usage for reads
   public static final String DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_KEY = "dfs.namenode.avoid.read.stale.datanode";
   public static final boolean DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_DEFAULT = false;
+  public static final String DFS_NAMENODE_AVOID_SLOW_DATANODE_FOR_READ_KEY =
+      "dfs.namenode.avoid.read.slow.datanode";
+  public static final boolean
+      DFS_NAMENODE_AVOID_SLOW_DATANODE_FOR_READ_DEFAULT = false;
   // Whether to enable datanode's stale state detection and usage for writes
   public static final String DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_WRITE_KEY = "dfs.namenode.avoid.write.stale.datanode";
   public static final boolean DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_WRITE_DEFAULT = false;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java

@@ -156,23 +156,36 @@ public int compare(DatanodeInfo a, DatanodeInfo b) {
 
   /**
    * Comparator for sorting DataNodeInfo[] based on
-   * stale, decommissioned and entering_maintenance states.
+   * slow, stale, entering_maintenance and decommissioned states.
-   * Order: live {@literal ->} stale {@literal ->} entering_maintenance
+   * Order: live {@literal ->} slow {@literal ->} stale {@literal ->}
-   * {@literal ->} decommissioned
+   * entering_maintenance {@literal ->} decommissioned
    */
   @InterfaceAudience.Private 
-  public static class ServiceAndStaleComparator extends ServiceComparator {
+  public static class StaleAndSlowComparator extends ServiceComparator {
+    private final boolean avoidStaleDataNodesForRead;
     private final long staleInterval;
+    private final boolean avoidSlowDataNodesForRead;
+    private final Set<String> slowNodesUuidSet;
 
     /**
      * Constructor of ServiceAndStaleComparator
-     * 
+     * @param avoidStaleDataNodesForRead
+     *          Whether or not to avoid using stale DataNodes for reading.
      * @param interval
      *          The time interval for marking datanodes as stale is passed from
-     *          outside, since the interval may be changed dynamically
+     *          outside, since the interval may be changed dynamically.
+     * @param avoidSlowDataNodesForRead
+     *          Whether or not to avoid using slow DataNodes for reading.
+     * @param slowNodesUuidSet
+     *          Slow DataNodes UUID set.
      */
-    public ServiceAndStaleComparator(long interval) {
+    public StaleAndSlowComparator(
+        boolean avoidStaleDataNodesForRead, long interval,
+        boolean avoidSlowDataNodesForRead, Set<String> slowNodesUuidSet) {
+      this.avoidStaleDataNodesForRead = avoidStaleDataNodesForRead;
       this.staleInterval = interval;
+      this.avoidSlowDataNodesForRead = avoidSlowDataNodesForRead;
+      this.slowNodesUuidSet = slowNodesUuidSet;
     }
 
     @Override
@@ -183,9 +196,22 @@ public int compare(DatanodeInfo a, DatanodeInfo b) {
       }
 
       // Stale nodes will be moved behind the normal nodes
-      boolean aStale = a.isStale(staleInterval);
+      if (avoidStaleDataNodesForRead) {
-      boolean bStale = b.isStale(staleInterval);
+        boolean aStale = a.isStale(staleInterval);
-      return aStale == bStale ? 0 : (aStale ? 1 : -1);
+        boolean bStale = b.isStale(staleInterval);
+        ret = aStale == bStale ? 0 : (aStale ? 1 : -1);
+        if (ret != 0) {
+          return ret;
+        }
+      }
+
+      // Slow nodes will be moved behind the normal nodes
+      if (avoidSlowDataNodesForRead) {
+        boolean aSlow = slowNodesUuidSet.contains(a.getDatanodeUuid());
+        boolean bSlow = slowNodesUuidSet.contains(b.getDatanodeUuid());
+        ret = aSlow == bSlow ? 0 : (aSlow ? 1 : -1);
+      }
+      return ret;
     }
   }    
     

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

@@ -1104,8 +1104,8 @@ boolean isGoodDatanode(DatanodeDescriptor node,
 
     // check if the target is a slow node
     if (dataNodePeerStatsEnabled && excludeSlowNodesEnabled) {
-      Set<Node> nodes = DatanodeManager.getSlowNodes();
+      Set<String> slowNodesUuidSet = DatanodeManager.getSlowNodesUuidSet();
-      if (nodes.contains(node)) {
+      if (slowNodesUuidSet.contains(node.getDatanodeUuid())) {
         logNodeIsNotChosen(node, NodeNotChosenReason.NODE_SLOW);
         return false;
       }

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

@@ -140,6 +140,9 @@ public class DatanodeManager {
   /** Whether or not to avoid using stale DataNodes for reading */
   private final boolean avoidStaleDataNodesForRead;
 
+  /** Whether or not to avoid using slow DataNodes for reading. */
+  private final boolean avoidSlowDataNodesForRead;
+
   /** Whether or not to consider lad for reading. */
   private final boolean readConsiderLoad;
 
@@ -210,7 +213,7 @@ public class DatanodeManager {
 
   @Nullable
   private final SlowPeerTracker slowPeerTracker;
-  private static Set<Node> slowNodesSet = Sets.newConcurrentHashSet();
+  private static Set<String> slowNodesUuidSet = Sets.newConcurrentHashSet();
   private Daemon slowPeerCollectorDaemon;
   private final long slowPeerCollectionInterval;
   private final int maxSlowPeerReportNodes;
@@ -242,7 +245,6 @@ public class DatanodeManager {
     } else {
       networktopology = NetworkTopology.getInstance(conf);
     }
-
     this.heartbeatManager = new HeartbeatManager(namesystem,
         blockManager, conf);
     this.datanodeAdminManager = new DatanodeAdminManager(namesystem,
@@ -273,7 +275,6 @@ public class DatanodeManager {
     }
     this.slowDiskTracker = dataNodeDiskStatsEnabled ?
         new SlowDiskTracker(conf, timer) : null;
-
     this.defaultXferPort = NetUtils.createSocketAddr(
           conf.getTrimmed(DFSConfigKeys.DFS_DATANODE_ADDRESS_KEY,
               DFSConfigKeys.DFS_DATANODE_ADDRESS_DEFAULT)).getPort();
@@ -294,11 +295,9 @@ public class DatanodeManager {
     } catch (IOException e) {
       LOG.error("error reading hosts files: ", e);
     }
-
     this.dnsToSwitchMapping = ReflectionUtils.newInstance(
         conf.getClass(DFSConfigKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY, 
             ScriptBasedMapping.class, DNSToSwitchMapping.class), conf);
-    
     this.rejectUnresolvedTopologyDN = conf.getBoolean(
         DFSConfigKeys.DFS_REJECT_UNRESOLVED_DN_TOPOLOGY_MAPPING_KEY,
         DFSConfigKeys.DFS_REJECT_UNRESOLVED_DN_TOPOLOGY_MAPPING_DEFAULT);
@@ -313,7 +312,6 @@ public class DatanodeManager {
       }
       dnsToSwitchMapping.resolve(locations);
     }
-
     heartbeatIntervalSeconds = conf.getTimeDuration(
         DFSConfigKeys.DFS_HEARTBEAT_INTERVAL_KEY,
         DFSConfigKeys.DFS_HEARTBEAT_INTERVAL_DEFAULT, TimeUnit.SECONDS);
@@ -322,7 +320,6 @@ public class DatanodeManager {
         DFSConfigKeys.DFS_NAMENODE_HEARTBEAT_RECHECK_INTERVAL_DEFAULT); // 5 minutes
     this.heartbeatExpireInterval = 2 * heartbeatRecheckInterval
         + 10 * 1000 * heartbeatIntervalSeconds;
-
     // Effected block invalidate limit is the bigger value between
     // value configured in hdfs-site.xml, and 20 * HB interval.
     final int configuredBlockInvalidateLimit = conf.getInt(
@@ -335,16 +332,17 @@ public class DatanodeManager {
         + ": configured=" + configuredBlockInvalidateLimit
         + ", counted=" + countedBlockInvalidateLimit
         + ", effected=" + blockInvalidateLimit);
-
     this.checkIpHostnameInRegistration = conf.getBoolean(
         DFSConfigKeys.DFS_NAMENODE_DATANODE_REGISTRATION_IP_HOSTNAME_CHECK_KEY,
         DFSConfigKeys.DFS_NAMENODE_DATANODE_REGISTRATION_IP_HOSTNAME_CHECK_DEFAULT);
     LOG.info(DFSConfigKeys.DFS_NAMENODE_DATANODE_REGISTRATION_IP_HOSTNAME_CHECK_KEY
         + "=" + checkIpHostnameInRegistration);
-
     this.avoidStaleDataNodesForRead = conf.getBoolean(
         DFSConfigKeys.DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_KEY,
         DFSConfigKeys.DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_DEFAULT);
+    this.avoidSlowDataNodesForRead = conf.getBoolean(
+        DFSConfigKeys.DFS_NAMENODE_AVOID_SLOW_DATANODE_FOR_READ_KEY,
+        DFSConfigKeys.DFS_NAMENODE_AVOID_SLOW_DATANODE_FOR_READ_DEFAULT);
     this.readConsiderLoad = conf.getBoolean(
         DFSConfigKeys.DFS_NAMENODE_READ_CONSIDERLOAD_KEY,
         DFSConfigKeys.DFS_NAMENODE_READ_CONSIDERLOAD_DEFAULT);
@@ -389,7 +387,7 @@ private void startSlowPeerCollector() {
       public void run() {
         while (true) {
           try {
-            slowNodesSet = getSlowPeers();
+            slowNodesUuidSet = getSlowPeersUuidSet();
           } catch (Exception e) {
             LOG.error("Failed to collect slow peers", e);
           }
@@ -509,12 +507,16 @@ private boolean isInactive(DatanodeInfo datanode) {
     return datanode.isDecommissioned() || datanode.isEnteringMaintenance() ||
         (avoidStaleDataNodesForRead && datanode.isStale(staleInterval));
   }
+
+  private boolean isSlowNode(String dnUuid) {
+    return avoidSlowDataNodesForRead && slowNodesUuidSet.contains(dnUuid);
+  }
   
   /**
    * Sort the non-striped located blocks by the distance to the target host.
    *
-   * For striped blocks, it will only move decommissioned/stale nodes to the
+   * For striped blocks, it will only move decommissioned/stale/slow
-   * bottom. For example, assume we have storage list:
+   * nodes to the bottom. For example, assume we have storage list:
    * d0, d1, d2, d3, d4, d5, d6, d7, d8, d9
    * mapping to block indices:
    * 0, 1, 2, 3, 4, 5, 6, 7, 8, 2
@@ -526,8 +528,11 @@ private boolean isInactive(DatanodeInfo datanode) {
    */
   public void sortLocatedBlocks(final String targetHost,
       final List<LocatedBlock> locatedBlocks) {
-    Comparator<DatanodeInfo> comparator = avoidStaleDataNodesForRead ?
+    Comparator<DatanodeInfo> comparator =
-        new DFSUtil.ServiceAndStaleComparator(staleInterval) :
+        avoidStaleDataNodesForRead || avoidSlowDataNodesForRead ?
+        new DFSUtil.StaleAndSlowComparator(
+            avoidStaleDataNodesForRead, staleInterval,
+            avoidSlowDataNodesForRead, slowNodesUuidSet) :
         new DFSUtil.ServiceComparator();
     // sort located block
     for (LocatedBlock lb : locatedBlocks) {
@@ -540,7 +545,8 @@ public void sortLocatedBlocks(final String targetHost,
   }
 
   /**
-   * Move decommissioned/stale datanodes to the bottom. After sorting it will
+   * Move decommissioned/entering_maintenance/stale/slow
+   * datanodes to the bottom. After sorting it will
    * update block indices and block tokens respectively.
    *
    * @param lb located striped block
@@ -571,8 +577,9 @@ private void sortLocatedStripedBlock(final LocatedBlock lb,
   }
 
   /**
-   * Move decommissioned/entering_maintenance/stale datanodes to the bottom.
+   * Move decommissioned/entering_maintenance/stale/slow
-   * Also, sort nodes by network distance.
+   * datanodes to the bottom. Also, sort nodes by network
+   * distance.
    *
    * @param lb located block
    * @param targetHost target host
@@ -602,12 +609,15 @@ private void sortLocatedBlock(final LocatedBlock lb, String targetHost,
     }
 
     DatanodeInfoWithStorage[] di = lb.getLocations();
-    // Move decommissioned/entering_maintenance/stale datanodes to the bottom
+    // Move decommissioned/entering_maintenance/stale/slow
+    // datanodes to the bottom
     Arrays.sort(di, comparator);
 
     // Sort nodes by network distance only for located blocks
     int lastActiveIndex = di.length - 1;
-    while (lastActiveIndex > 0 && isInactive(di[lastActiveIndex])) {
+    while (lastActiveIndex > 0 && (
+        isSlowNode(di[lastActiveIndex].getDatanodeUuid()) ||
+            isInactive(di[lastActiveIndex]))) {
       --lastActiveIndex;
     }
     int activeLen = lastActiveIndex + 1;
@@ -2083,10 +2093,10 @@ public String getSlowPeersReport() {
    * Returns all tracking slow peers.
    * @return
    */
-  public Set<Node> getSlowPeers() {
+  public Set<String> getSlowPeersUuidSet() {
-    Set<Node> slowPeersSet = Sets.newConcurrentHashSet();
+    Set<String> slowPeersUuidSet = Sets.newConcurrentHashSet();
     if (slowPeerTracker == null) {
-      return slowPeersSet;
+      return slowPeersUuidSet;
     }
     ArrayList<String> slowNodes =
         slowPeerTracker.getSlowNodes(maxSlowPeerReportNodes);
@@ -2099,18 +2109,18 @@ public Set<Node> getSlowPeers() {
       DatanodeDescriptor datanodeByHost =
           host2DatanodeMap.getDatanodeByHost(ipAddr);
       if (datanodeByHost != null) {
-        slowPeersSet.add(datanodeByHost);
+        slowPeersUuidSet.add(datanodeByHost.getDatanodeUuid());
       }
     }
-    return slowPeersSet;
+    return slowPeersUuidSet;
   }
 
   /**
-   * Returns all tracking slow peers.
+   * Returns all tracking slow datanodes uuids.
    * @return
    */
-  public static Set<Node> getSlowNodes() {
+  public static Set<String> getSlowNodesUuidSet() {
-    return slowNodesSet;
+    return slowNodesUuidSet;
   }
 
   /**
@@ -2128,6 +2138,12 @@ public SlowPeerTracker getSlowPeerTracker() {
   public SlowDiskTracker getSlowDiskTracker() {
     return slowDiskTracker;
   }
+
+  @VisibleForTesting
+  public void addSlowPeers(String dnUuid) {
+    slowNodesUuidSet.add(dnUuid);
+  }
+
   /**
    * Retrieve information about slow disks as a JSON.
    * Returns null if we are not tracking slow disks.

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -2110,6 +2110,16 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.namenode.avoid.read.slow.datanode</name>
+  <value>false</value>
+  <description>
+    Indicate whether or not to avoid reading from &quot;slow&quot; datanodes.
+    Slow datanodes will be moved to the end of the node list returned
+    for reading.
+  </description>
+</property>
+
 <property>
   <name>dfs.namenode.avoid.write.stale.datanode</name>
   <value>false</value>

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

@@ -22,7 +22,6 @@
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.TestBlockStoragePolicy;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
-import org.apache.hadoop.net.Node;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
@@ -100,12 +99,12 @@ public void testChooseTargetExcludeSlowNodes() throws Exception {
       Thread.sleep(3000);
 
       // fetch slow nodes
-      Set<Node> slowPeers = dnManager.getSlowPeers();
+      Set<String> slowPeers = dnManager.getSlowPeersUuidSet();
 
       // assert slow nodes
       assertEquals(3, slowPeers.size());
       for (int i = 0; i < slowPeers.size(); i++) {
-        assertTrue(slowPeers.contains(dataNodes[i]));
+        assertTrue(slowPeers.contains(dataNodes[i].getDatanodeUuid()));
       }
 
       // mock writer
@@ -120,7 +119,8 @@ public void testChooseTargetExcludeSlowNodes() throws Exception {
       // assert targets
       assertEquals(3, targets.length);
       for (int i = 0; i < targets.length; i++) {
-        assertTrue(!slowPeers.contains(targets[i].getDatanodeDescriptor()));
+        assertTrue(!slowPeers.contains(targets[i].getDatanodeDescriptor()
+            .getDatanodeUuid()));
       }
     } finally {
       namenode.getNamesystem().writeUnlock();

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

@@ -27,34 +27,24 @@
 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
 import org.apache.hadoop.util.Time;
-import org.junit.BeforeClass;
 import org.junit.Test;
 import org.mockito.Mockito;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Date;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 /**
  * This class tests the sorting of located blocks based on
  * multiple states.
  */
 public class TestSortLocatedBlock {
-  static final Logger LOG = LoggerFactory
-      .getLogger(TestSortLocatedBlock.class);
 
-  private static DatanodeManager dm;
   private static final long STALE_INTERVAL = 30 * 1000 * 60;
 
-  @BeforeClass
-  public static void setup() throws IOException {
-    dm = mockDatanodeManager();
-  }
-
   /**
    * Test to verify sorting with multiple state
    * datanodes exists in storage lists.
@@ -73,8 +63,7 @@ public static void setup() throws IOException {
    * (d4 -> d3 -> d1 -> d2 -> d0).
    */
   @Test(timeout = 30000)
-  public void testWithMultipleStateDatanodes() {
+  public void testWithStaleDatanodes() throws IOException {
-    LOG.info("Starting test testWithMultipleStateDatanodes");
     long blockID = Long.MIN_VALUE;
     int totalDns = 5;
     DatanodeInfo[] locs = new DatanodeInfo[totalDns];
@@ -106,6 +95,7 @@ public void testWithMultipleStateDatanodes() {
         1024L, new Date().getTime()), locs));
 
     // sort located blocks
+    DatanodeManager dm = mockDatanodeManager(true, false);
     dm.sortLocatedBlocks(null, locatedBlocks);
 
     // get locations after sorting
@@ -114,6 +104,9 @@ public void testWithMultipleStateDatanodes() {
 
     // assert location order:
     // live -> stale -> entering_maintenance -> decommissioned
+    // (d4 -> d3 -> d1 -> d0 -> d2)
+    // or
+    // (d4 -> d3 -> d1 -> d2 -> d0).
     // live
     assertEquals(locs[4].getIpAddr(), locations[0].getIpAddr());
     // stale
@@ -126,11 +119,188 @@ public void testWithMultipleStateDatanodes() {
         && decommissionedNodes.contains(locations[4]));
   }
 
-  private static DatanodeManager mockDatanodeManager() throws IOException {
+  /**
+   * Test to verify sorting with multiple state
+   * datanodes exists in storage lists.
+   *
+   * After sorting the expected datanodes list will be:
+   * live -> slow -> stale -> staleAndSlow ->
+   * entering_maintenance -> decommissioned.
+   *
+   * avoidStaleDataNodesForRead=true && avoidSlowDataNodesForRead=true
+   * d5 -> d4 -> d3 -> d2 -> d1 -> d0
+   */
+  @Test(timeout = 30000)
+  public void testAviodStaleAndSlowDatanodes() throws IOException {
+    DatanodeManager dm = mockDatanodeManager(true, true);
+    DatanodeInfo[] locs = mockDatanodes(dm);
+
+    ArrayList<LocatedBlock> locatedBlocks = new ArrayList<>();
+    locatedBlocks.add(new LocatedBlock(
+        new ExtendedBlock("pool", Long.MIN_VALUE,
+            1024L, new Date().getTime()), locs));
+
+    // sort located blocks
+    dm.sortLocatedBlocks(null, locatedBlocks);
+
+    // get locations after sorting
+    LocatedBlock locatedBlock = locatedBlocks.get(0);
+    DatanodeInfoWithStorage[] locations = locatedBlock.getLocations();
+
+    // assert location order:
+    // live -> stale -> entering_maintenance -> decommissioned
+    // live
+    assertEquals(locs[5].getIpAddr(), locations[0].getIpAddr());
+    // slow
+    assertEquals(locs[4].getIpAddr(), locations[1].getIpAddr());
+    // stale
+    assertEquals(locs[3].getIpAddr(), locations[2].getIpAddr());
+    // stale and slow
+    assertEquals(locs[2].getIpAddr(), locations[3].getIpAddr());
+    // entering_maintenance
+    assertEquals(locs[1].getIpAddr(), locations[4].getIpAddr());
+    // decommissioned
+    assertEquals(locs[0].getIpAddr(), locations[5].getIpAddr());
+  }
+
+  /**
+   * Test to verify sorting with multiple state
+   * datanodes exists in storage lists.
+   *
+   * After sorting the expected datanodes list will be:
+   * (live <-> slow) -> (stale <-> staleAndSlow) ->
+   * entering_maintenance -> decommissioned.
+   *
+   * avoidStaleDataNodesForRead=true && avoidSlowDataNodesForRead=false
+   * (d5 <-> d4) -> (d3 <-> d2) -> d1 -> d0
+   */
+  @Test(timeout = 30000)
+  public void testAviodStaleDatanodes() throws IOException {
+    DatanodeManager dm = mockDatanodeManager(true, false);
+    DatanodeInfo[] locs = mockDatanodes(dm);
+
+    ArrayList<LocatedBlock> locatedBlocks = new ArrayList<>();
+    locatedBlocks.add(new LocatedBlock(
+        new ExtendedBlock("pool", Long.MIN_VALUE,
+            1024L, new Date().getTime()), locs));
+
+    // sort located blocks
+    dm.sortLocatedBlocks(null, locatedBlocks);
+
+    // get locations after sorting
+    LocatedBlock locatedBlock = locatedBlocks.get(0);
+    DatanodeInfoWithStorage[] locations = locatedBlock.getLocations();
+
+    // assert location order:
+    // live -> stale -> entering_maintenance -> decommissioned
+    // live
+    assertTrue((locs[5].getIpAddr() == locations[0].getIpAddr() &&
+        locs[4].getIpAddr() == locations[1].getIpAddr()) ||
+        (locs[5].getIpAddr() == locations[1].getIpAddr() &&
+            locs[4].getIpAddr() == locations[0].getIpAddr()));
+    // stale
+    assertTrue((locs[3].getIpAddr() == locations[2].getIpAddr() &&
+        locs[2].getIpAddr() == locations[3].getIpAddr()) ||
+        (locs[3].getIpAddr() == locations[3].getIpAddr() &&
+            locs[2].getIpAddr() == locations[2].getIpAddr()));
+    // entering_maintenance
+    assertEquals(locs[1].getIpAddr(), locations[4].getIpAddr());
+    // decommissioned
+    assertEquals(locs[0].getIpAddr(), locations[5].getIpAddr());
+  }
+
+  /**
+   * Test to verify sorting with multiple state
+   * datanodes exists in storage lists.
+   *
+   * After sorting the expected datanodes list will be:
+   * (live <-> stale) -> (slow <-> staleAndSlow) ->
+   * entering_maintenance -> decommissioned.
+   *
+   * avoidStaleDataNodesForRead=false && avoidSlowDataNodesForRead=true
+   * (d5 -> d3) -> (d4 <-> d2) -> d1 -> d0
+   */
+  @Test(timeout = 30000)
+  public void testAviodSlowDatanodes() throws IOException {
+    DatanodeManager dm = mockDatanodeManager(false, true);
+    DatanodeInfo[] locs = mockDatanodes(dm);
+
+    ArrayList<LocatedBlock> locatedBlocks = new ArrayList<>();
+    locatedBlocks.add(new LocatedBlock(
+        new ExtendedBlock("pool", Long.MIN_VALUE,
+            1024L, new Date().getTime()), locs));
+
+    // sort located blocks
+    dm.sortLocatedBlocks(null, locatedBlocks);
+
+    // get locations after sorting
+    LocatedBlock locatedBlock = locatedBlocks.get(0);
+    DatanodeInfoWithStorage[] locations = locatedBlock.getLocations();
+
+    // assert location order:
+    // live -> slow -> entering_maintenance -> decommissioned
+    // live
+    assertTrue((locs[5].getIpAddr() == locations[0].getIpAddr() &&
+        locs[3].getIpAddr() == locations[1].getIpAddr()) ||
+        (locs[5].getIpAddr() == locations[1].getIpAddr() &&
+            locs[3].getIpAddr() == locations[0].getIpAddr()));
+    // slow
+    assertTrue((locs[4].getIpAddr() == locations[2].getIpAddr() &&
+        locs[2].getIpAddr() == locations[3].getIpAddr()) ||
+        (locs[4].getIpAddr() == locations[3].getIpAddr() &&
+            locs[2].getIpAddr() == locations[2].getIpAddr()));
+    // entering_maintenance
+    assertEquals(locs[1].getIpAddr(), locations[4].getIpAddr());
+    // decommissioned
+    assertEquals(locs[0].getIpAddr(), locations[5].getIpAddr());
+  }
+
+  /**
+   * We mock the following list of datanodes, and create LocatedBlock.
+   * d0 - decommissioned
+   * d1 - entering_maintenance
+   * d2 - stale and slow
+   * d3 - stale
+   * d4 - slow
+   * d5 - live(in-service)
+   */
+  private static DatanodeInfo[] mockDatanodes(DatanodeManager dm) {
+    int totalDns = 6;
+    DatanodeInfo[] locs = new DatanodeInfo[totalDns];
+
+    // create datanodes
+    for (int i = 0; i < totalDns; i++) {
+      String ip = i + "." + i + "." + i + "." + i;
+      locs[i] = DFSTestUtil.getDatanodeInfo(ip);
+      locs[i].setLastUpdateMonotonic(Time.monotonicNow());
+    }
+    // set decommissioned state
+    locs[0].setDecommissioned();
+    // set entering_maintenance state
+    locs[1].startMaintenance();
+    // set stale and slow state
+    locs[2].setLastUpdateMonotonic(Time.monotonicNow() -
+        DFSConfigKeys.DFS_NAMENODE_STALE_DATANODE_INTERVAL_DEFAULT * 1000 - 1);
+    dm.addSlowPeers(locs[2].getDatanodeUuid());
+    // set stale state
+    locs[3].setLastUpdateMonotonic(Time.monotonicNow() -
+        DFSConfigKeys.DFS_NAMENODE_STALE_DATANODE_INTERVAL_DEFAULT * 1000 - 1);
+    // set slow state
+    dm.addSlowPeers(locs[4].getDatanodeUuid());
+
+    return locs;
+  }
+
+  private static DatanodeManager mockDatanodeManager(
+      boolean avoidStaleDNForRead, boolean avoidSlowDNForRead)
+      throws IOException {
     Configuration conf = new Configuration();
     conf.setBoolean(
         DFSConfigKeys.DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_KEY,
-        true);
+        avoidStaleDNForRead);
+    conf.setBoolean(
+        DFSConfigKeys.DFS_NAMENODE_AVOID_SLOW_DATANODE_FOR_READ_KEY,
+        avoidSlowDNForRead);
     conf.setLong(DFSConfigKeys.DFS_NAMENODE_STALE_DATANODE_INTERVAL_KEY,
         STALE_INTERVAL);
     FSNamesystem fsn = Mockito.mock(FSNamesystem.class);