HDFS-17332 DFSInputStream: avoid logging stacktrace until when we really need to fail a read request with a MissingBlockException (#6446)

Print a warn log message for read retries and only print the full stack trace for a read request failure.

Contributed by: Xing Lin

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -771,7 +771,7 @@ public synchronized int read() throws IOException {
    * ChecksumFileSystem
    */
   private synchronized int readBuffer(ReaderStrategy reader, int len,
-                                      CorruptedBlocks corruptedBlocks)
+      CorruptedBlocks corruptedBlocks, final Map<InetSocketAddress, List<IOException>> exceptionMap)
       throws IOException {
     IOException ioe;
 
@@ -786,6 +786,7 @@ private synchronized int readBuffer(ReaderStrategy reader, int len,
     while (true) {
       // retry as many times as seekToNewSource allows.
       try {
+        DFSClientFaultInjector.get().fetchFromDatanodeException();
         return reader.readFromBlock(blockReader, len);
       } catch (ChecksumException ce) {
         DFSClient.LOG.warn("Found Checksum error for "
@@ -796,11 +797,18 @@ private synchronized int readBuffer(ReaderStrategy reader, int len,
         // we want to remember which block replicas we have tried
         corruptedBlocks.addCorruptedBlock(getCurrentBlock(), currentNode);
       } catch (IOException e) {
-        if (!retryCurrentNode) {
+        String msg = String.format("Failed to read block %s for file %s from datanode %s. "
-          DFSClient.LOG.warn("Exception while reading from "
+                + "Exception is %s. Retry with the current or next available datanode.",
-              + getCurrentBlock() + " of " + src + " from "
+            getCurrentBlock().getBlockName(), src, currentNode.getXferAddr(), e);
-              + currentNode, e);
+        DFSClient.LOG.warn(msg);
+
+        // Add the exception to exceptionMap for this datanode.
+        InetSocketAddress datanode = currentNode.getResolvedAddress();
+        if (!exceptionMap.containsKey(datanode)) {
+          exceptionMap.put(datanode, new LinkedList<IOException>());
         }
+        exceptionMap.get(datanode).add(e);
+
         ioe = e;
       }
       boolean sourceFound;
@@ -822,6 +830,29 @@ private synchronized int readBuffer(ReaderStrategy reader, int len,
     }
   }
 
+  /**
+   * Send IOExceptions happened at each individual datanode to DFSClient.LOG for a failed read
+   * request. Used in both readWithStrategy() and pread(), to record the exceptions when a read
+   * request failed to be served.
+   * @param position offset in the file where we fail to read
+   * @param exceptionMap a map which stores the list of IOExceptions for each datanode
+   */
+  private void logDataNodeExceptionsOnReadError(long position, final Map<InetSocketAddress,
+      List<IOException>> exceptionMap) {
+    String msg = String.format("Failed to read from all available datanodes for file %s "
+        + "at position=%d after retrying.", src, position);
+    DFSClient.LOG.error(msg);
+    for (Map.Entry<InetSocketAddress, List<IOException>> dataNodeExceptions :
+        exceptionMap.entrySet()) {
+      List<IOException> exceptions = dataNodeExceptions.getValue();
+      for (IOException ex : exceptions) {
+        msg = String.format("Exception when fetching file %s at position=%d at datanode %s:", src,
+            position, dataNodeExceptions.getKey());
+        DFSClient.LOG.error(msg, ex);
+      }
+    }
+  }
+
   protected synchronized int readWithStrategy(ReaderStrategy strategy)
       throws IOException {
     dfsClient.checkOpen();
@@ -831,6 +862,9 @@ protected synchronized int readWithStrategy(ReaderStrategy strategy)
 
     int len = strategy.getTargetLength();
     CorruptedBlocks corruptedBlocks = new CorruptedBlocks();
+    // A map to record IOExceptions when fetching from each datanode. Key is the socketAddress of
+    // a datanode.
+    Map<InetSocketAddress, List<IOException>> exceptionMap = new HashMap<>();
     failures = 0;
 
     maybeRegisterBlockRefresh();
@@ -852,7 +886,7 @@ protected synchronized int readWithStrategy(ReaderStrategy strategy)
             }
           }
           long beginReadMS = Time.monotonicNow();
-          int result = readBuffer(strategy, realLen, corruptedBlocks);
+          int result = readBuffer(strategy, realLen, corruptedBlocks, exceptionMap);
           long readTimeMS = Time.monotonicNow() - beginReadMS;
           if (result >= 0) {
             pos += result;
@@ -880,6 +914,8 @@ protected synchronized int readWithStrategy(ReaderStrategy strategy)
             dfsClient.addNodeToDeadNodeDetector(this, currentNode);
           }
           if (--retries == 0) {
+            // Fail the request and log all exceptions
+            logDataNodeExceptionsOnReadError(pos, exceptionMap);
             throw e;
           }
         } finally {
@@ -1122,8 +1158,8 @@ private static String getBestNodeDNAddrPairErrorString(
     return errMsgr.toString();
   }
 
-  protected void fetchBlockByteRange(LocatedBlock block, long start, long end,
+  protected void fetchBlockByteRange(LocatedBlock block, long start, long end, ByteBuffer buf,
-      ByteBuffer buf, CorruptedBlocks corruptedBlocks)
+      CorruptedBlocks corruptedBlocks, final Map<InetSocketAddress, List<IOException>> exceptionMap)
       throws IOException {
     while (true) {
       DNAddrPair addressPair = chooseDataNode(block, null);
@@ -1131,7 +1167,7 @@ protected void fetchBlockByteRange(LocatedBlock block, long start, long end,
       block = addressPair.block;
       try {
         actualGetFromOneDataNode(addressPair, start, end, buf,
-            corruptedBlocks);
+            corruptedBlocks, exceptionMap);
         return;
       } catch (IOException e) {
         checkInterrupted(e); // check if the read has been interrupted
@@ -1142,15 +1178,15 @@ protected void fetchBlockByteRange(LocatedBlock block, long start, long end,
   }
 
   private Callable<ByteBuffer> getFromOneDataNode(final DNAddrPair datanode,
-      final LocatedBlock block, final long start, final long end,
+      final long start, final long end,
       final ByteBuffer bb,
       final CorruptedBlocks corruptedBlocks,
-      final int hedgedReadId) {
+      final Map<InetSocketAddress, List<IOException>> exceptionMap) {
     return new Callable<ByteBuffer>() {
       @Override
       public ByteBuffer call() throws Exception {
         DFSClientFaultInjector.get().sleepBeforeHedgedGet();
-        actualGetFromOneDataNode(datanode, start, end, bb, corruptedBlocks);
+        actualGetFromOneDataNode(datanode, start, end, bb, corruptedBlocks, exceptionMap);
         return bb;
       }
     };
@@ -1167,7 +1203,8 @@ public ByteBuffer call() throws Exception {
    *                          block replica
    */
   void actualGetFromOneDataNode(final DNAddrPair datanode, final long startInBlk,
-      final long endInBlk, ByteBuffer buf, CorruptedBlocks corruptedBlocks)
+      final long endInBlk, ByteBuffer buf, CorruptedBlocks corruptedBlocks,
+      final Map<InetSocketAddress, List<IOException>> exceptionMap)
       throws IOException {
     DFSClientFaultInjector.get().startFetchFromDatanode();
     int refetchToken = 1; // only need to get a new access token once
@@ -1236,9 +1273,16 @@ void actualGetFromOneDataNode(final DNAddrPair datanode, final long startInBlk,
             // ignore IOE, since we can retry it later in a loop
           }
         } else {
-          String msg = "Failed to connect to " + datanode.addr + " for file "
+          String msg = String.format("Failed to read block %s for file %s from datanode %s. "
-              + src + " for block " + block.getBlock() + ":" + e;
+                  + "Exception is %s. Retry with the next available datanode.",
-          DFSClient.LOG.warn("Connection failure: " + msg, e);
+              block.getBlock().getBlockName(), src, datanode.addr, e);
+          DFSClient.LOG.warn(msg);
+
+          // Add the exception to the exceptionMap
+          if (!exceptionMap.containsKey(datanode.addr)) {
+            exceptionMap.put(datanode.addr, new LinkedList<IOException>());
+          }
+          exceptionMap.get(datanode.addr).add(e);
           addToLocalDeadNodes(datanode.info);
           dfsClient.addNodeToDeadNodeDetector(this, datanode.info);
           throw new IOException(msg);
@@ -1270,9 +1314,9 @@ protected LocatedBlock refreshLocatedBlock(LocatedBlock block)
    * 'hedged' read if the first read is taking longer than configured amount of
    * time. We then wait on which ever read returns first.
    */
-  private void hedgedFetchBlockByteRange(LocatedBlock block, long start,
+  private void hedgedFetchBlockByteRange(LocatedBlock block, long start, long end, ByteBuffer buf,
-      long end, ByteBuffer buf, CorruptedBlocks corruptedBlocks)
+      CorruptedBlocks corruptedBlocks,
-      throws IOException {
+      final Map<InetSocketAddress, List<IOException>> exceptionMap) throws IOException {
     final DfsClientConf conf = dfsClient.getConf();
     ArrayList<Future<ByteBuffer>> futures = new ArrayList<>();
     CompletionService<ByteBuffer> hedgedService =
@@ -1280,7 +1324,6 @@ private void hedgedFetchBlockByteRange(LocatedBlock block, long start,
     ArrayList<DatanodeInfo> ignored = new ArrayList<>();
     ByteBuffer bb;
     int len = (int) (end - start + 1);
-    int hedgedReadId = 0;
     while (true) {
       // see HDFS-6591, this metric is used to verify/catch unnecessary loops
       hedgedReadOpsLoopNumForTesting++;
@@ -1293,9 +1336,8 @@ private void hedgedFetchBlockByteRange(LocatedBlock block, long start,
         // Latest block, if refreshed internally
         block = chosenNode.block;
         bb = ByteBuffer.allocate(len);
-        Callable<ByteBuffer> getFromDataNodeCallable = getFromOneDataNode(
+        Callable<ByteBuffer> getFromDataNodeCallable =
-            chosenNode, block, start, end, bb,
+            getFromOneDataNode(chosenNode, start, end, bb, corruptedBlocks, exceptionMap);
-            corruptedBlocks, hedgedReadId++);
         Future<ByteBuffer> firstRequest = hedgedService
             .submit(getFromDataNodeCallable);
         futures.add(firstRequest);
@@ -1335,8 +1377,7 @@ private void hedgedFetchBlockByteRange(LocatedBlock block, long start,
             block = chosenNode.block;
             bb = ByteBuffer.allocate(len);
             Callable<ByteBuffer> getFromDataNodeCallable =
-                getFromOneDataNode(chosenNode, block, start, end, bb,
+                getFromOneDataNode(chosenNode, start, end, bb, corruptedBlocks, exceptionMap);
-                    corruptedBlocks, hedgedReadId++);
             Future<ByteBuffer> oneMoreRequest =
                 hedgedService.submit(getFromDataNodeCallable);
             futures.add(oneMoreRequest);
@@ -1486,6 +1527,11 @@ private int pread(long position, ByteBuffer buffer)
     List<LocatedBlock> blockRange = getBlockRange(position, realLen);
     int remaining = realLen;
     CorruptedBlocks corruptedBlocks = new CorruptedBlocks();
+    // A map to record all IOExceptions happened at each datanode when fetching a block.
+    // In HDFS-17332, we worked on populating this map only for DFSInputStream, but not for
+    // DFSStripedInputStream. If you need the same function for DFSStripedInputStream, please
+    // work on it yourself (fetchBlockByteRange() in DFSStripedInputStream).
+    Map<InetSocketAddress, List<IOException>> exceptionMap = new HashMap<>();
     for (LocatedBlock blk : blockRange) {
       long targetStart = position - blk.getStartOffset();
       int bytesToRead = (int) Math.min(remaining,
@@ -1494,11 +1540,17 @@ private int pread(long position, ByteBuffer buffer)
       try {
         if (dfsClient.isHedgedReadsEnabled() && !blk.isStriped()) {
           hedgedFetchBlockByteRange(blk, targetStart,
-              targetEnd, buffer, corruptedBlocks);
+              targetEnd, buffer, corruptedBlocks, exceptionMap);
         } else {
           fetchBlockByteRange(blk, targetStart, targetEnd,
-              buffer, corruptedBlocks);
+              buffer, corruptedBlocks, exceptionMap);
         }
+      } catch (IOException e) {
+        // When we reach here, it means we fail to fetch the current block from all available
+        // datanodes. Send IOExceptions in exceptionMap to the log and rethrow the exception to
+        // fail this request.
+        logDataNodeExceptionsOnReadError(position, exceptionMap);
+        throw e;
       } finally {
         // Check and report if any block replicas are corrupted.
         // BlockMissingException may be caught if all block replicas are
@@ -1507,6 +1559,8 @@ private int pread(long position, ByteBuffer buffer)
             false);
       }
 
+      // Reset exceptionMap before fetching the next block.
+      exceptionMap.clear();
       remaining -= bytesToRead;
       position += bytesToRead;
     }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java

@@ -17,6 +17,8 @@
  */
 package org.apache.hadoop.hdfs;
 
+import java.net.InetSocketAddress;
+import java.util.Map;
 import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.ReadOption;
@@ -479,10 +481,14 @@ private LocatedStripedBlock getBlockGroupAt(long offset) throws IOException {
 
   /**
    * Real implementation of pread.
+   * <p>
+   * Note: exceptionMap is not populated with ioExceptions as what we added for DFSInputStream. If
+   * you need this function, please implement it.
    */
   @Override
   protected void fetchBlockByteRange(LocatedBlock block, long start,
-      long end, ByteBuffer buf, CorruptedBlocks corruptedBlocks)
+      long end, ByteBuffer buf, CorruptedBlocks corruptedBlocks,
+      final Map<InetSocketAddress, List<IOException>> exceptionMap)
       throws IOException {
     // Refresh the striped block group
     LocatedStripedBlock blockGroup = getBlockGroupAt(block.getStartOffset());

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestPread.java

@@ -17,8 +17,10 @@
  */
 package org.apache.hadoop.hdfs;
 
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.io.EOFException;
 import java.io.IOException;
@@ -35,6 +37,7 @@
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.ChecksumException;
 import org.apache.hadoop.fs.FSDataInputStream;
@@ -52,6 +55,7 @@
 import org.apache.hadoop.test.GenericTestUtils;
 import org.junit.Assert;
 import org.junit.Before;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.mockito.Mockito;
 import org.mockito.invocation.InvocationOnMock;
@@ -76,7 +80,12 @@ public class TestPread {
 
   private static final Logger LOG =
       LoggerFactory.getLogger(TestPread.class.getName());
-
+  private final GenericTestUtils.LogCapturer dfsClientLog =
+      GenericTestUtils.LogCapturer.captureLogs(DFSClient.LOG);
+  @BeforeClass
+  public static void setLogLevel() {
+    GenericTestUtils.setLogLevel(DFSClient.LOG, org.apache.log4j.Level.WARN);
+  }
   @Before
   public void setup() {
     simulatedStorage = false;
@@ -556,6 +565,164 @@ public Void call() throws IOException {
     }
   }
 
+  /**
+   * Test logging in getFromOneDataNode when the number of IOExceptions can be recovered by
+   * retrying on a different datanode or by refreshing data nodes and retrying each data node one
+   * more time.
+   */
+  @Test(timeout=120000)
+  public void testGetFromOneDataNodeExceptionLogging() throws IOException {
+    // With maxBlockAcquireFailures = 0, we would try on each datanode only once and if
+    // we fail on all three datanodes, we fail the read request.
+    testGetFromOneDataNodeExceptionLogging(0, 0);
+    testGetFromOneDataNodeExceptionLogging(1, 0);
+    testGetFromOneDataNodeExceptionLogging(2, 0);
+
+    // With maxBlockAcquireFailures = 1, we will re-try each datanode a second time.
+    // So, we can tolerate up to 5 datanode fetch failures.
+    testGetFromOneDataNodeExceptionLogging(3, 1);
+    testGetFromOneDataNodeExceptionLogging(4, 1);
+    testGetFromOneDataNodeExceptionLogging(5, 1);
+  }
+
+  /**
+   * Each failed IOException would result in a WARN log of "Failed to connect to XXX. Retry with
+   * the next available datanode.". We verify the number of such log lines match the number of
+   * failed DNs.
+   * <p>
+   * @param ioExceptions number of IOExceptions to throw during a test.
+   * @param maxBlockAcquireFailures number of refreshLocation we would perform once we mark
+   *                                   all current data nodes as dead.
+   */
+  private void testGetFromOneDataNodeExceptionLogging(final int ioExceptions,
+      int maxBlockAcquireFailures)
+      throws IOException {
+    dfsClientLog.clearOutput();
+
+    if (ioExceptions < 0 || ioExceptions >= 3 * (maxBlockAcquireFailures+1)) {
+      return;
+    }
+
+    Configuration conf = new Configuration();
+    conf.setInt(DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY, maxBlockAcquireFailures);
+    final int[] count = {0};
+    // Set up the InjectionHandler
+    DFSClientFaultInjector.set(Mockito.mock(DFSClientFaultInjector.class));
+    DFSClientFaultInjector injector = DFSClientFaultInjector.get();
+    Mockito.doAnswer(new Answer<Void>() {
+      @Override
+      public Void answer(InvocationOnMock invocation) throws Throwable {
+        if (count[0] < ioExceptions) {
+          LOG.info("-------------- throw IOException " + count[0]);
+          count[0]++;
+          throw new IOException("IOException test");
+        }
+        return null;
+      }
+    }).when(injector).fetchFromDatanodeException();
+
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).format(true).build();
+    DistributedFileSystem fileSys = cluster.getFileSystem();
+    DFSClient dfsClient = fileSys.getClient();
+    DFSInputStream input = null;
+    Path file = new Path("/testfile.dat");
+
+    try {
+      DFSTestUtil.createFile(fileSys, file, fileSize, fileSize, blockSize, (short) 3, seed);
+
+      byte[] buffer = new byte[fileSize];
+      input = dfsClient.open(file.toString());
+      input.read(0, buffer, 0, fileSize);
+      assertEquals(ioExceptions, StringUtils.countMatches(dfsClientLog.getOutput(),
+          "Retry with the next available datanode."));
+    } finally {
+      Mockito.reset(injector);
+      IOUtils.cleanupWithLogger(LOG, input);
+      fileSys.close();
+      cluster.shutdown();
+      dfsClientLog.clearOutput();
+    }
+  }
+
+  /**
+   * Test the case where we always hit IOExceptions, causing the read request to fail.
+   */
+  @Test(timeout=60000)
+  public void testFetchFromDataNodeExceptionLoggingFailedRequest()
+      throws IOException {
+    testFetchFromDataNodeExceptionLoggingFailedRequest(0);
+    testFetchFromDataNodeExceptionLoggingFailedRequest(1);
+  }
+
+  /**
+   * We verify that BlockMissingException is threw and there is one ERROR log line of
+   * "Failed to read from all available datanodes for file"
+   * and 3 * (maxBlockAcquireFailures+1) ERROR log lines of
+   * "Exception when fetching file /testfile.dat at position".
+   * <p>
+   * maxBlockAcquireFailures determines how many times we can retry when we fail to read from
+   * all three data nodes.
+   * <ul>
+   *   <li>maxBlockAcquireFailures = 0: no retry. We will only read from each of the three
+   *   data nodes only once. We expect to see 3 ERROR log lines of "Exception when fetching file
+   *   /testfile.dat at position".
+   *   </li>
+   *   <li>maxBlockAcquireFailures = 1: 1 retry. We will read from each of the three data
+   *   nodes twice. We expect to see 6 ERROR log lines of "Exception when fetching file
+   *   /testfile.dat at position".
+   *   </li>
+   * </ul>
+   */
+  private void testFetchFromDataNodeExceptionLoggingFailedRequest(int maxBlockAcquireFailures)
+      throws IOException {
+    dfsClientLog.clearOutput();
+
+    Configuration conf = new Configuration();
+    conf.setInt(DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY, maxBlockAcquireFailures);
+    // Set up the InjectionHandler
+    DFSClientFaultInjector.set(Mockito.mock(DFSClientFaultInjector.class));
+    DFSClientFaultInjector injector = DFSClientFaultInjector.get();
+    Mockito.doAnswer(new Answer<Void>() {
+      @Override
+      public Void answer(InvocationOnMock invocation) throws Throwable {
+        LOG.info("-------------- throw IOException ");
+        throw new IOException("IOException test");
+      }
+    }).when(injector).fetchFromDatanodeException();
+
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).format(true).build();
+    DistributedFileSystem fileSys = cluster.getFileSystem();
+    DFSClient dfsClient = fileSys.getClient();
+    DFSInputStream input = null;
+    Path file = new Path("/testfile.dat");
+
+    try {
+      DFSTestUtil.createFile(fileSys, file, fileSize, fileSize, blockSize, (short) 3, seed);
+
+      byte[] buffer = new byte[fileSize];
+      input = dfsClient.open(file.toString());
+      input.read(0, buffer, 0, fileSize);
+      fail();
+    } catch (BlockMissingException expected) {
+      // Logging from pread
+      assertEquals(1, StringUtils.countMatches(dfsClientLog.getOutput(),
+          "Failed to read from all available datanodes for file"));
+      assertEquals(3 * (maxBlockAcquireFailures + 1),
+          StringUtils.countMatches(dfsClientLog.getOutput(),
+              "Exception when fetching file /testfile.dat at position"));
+      // Logging from actualGetFromOneDataNode
+      assertEquals(3 * (maxBlockAcquireFailures + 1),
+          StringUtils.countMatches(dfsClientLog.getOutput(),
+              "Retry with the next available datanode."));
+    } finally {
+      Mockito.reset(injector);
+      IOUtils.cleanupWithLogger(LOG, input);
+      fileSys.close();
+      cluster.shutdown();
+      dfsClientLog.clearOutput();
+    }
+  }
+
   @Test(timeout=30000)
   public void testHedgedReadFromAllDNFailed() throws IOException {
     Configuration conf = new Configuration();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestRead.java

@@ -25,6 +25,7 @@
 import java.nio.channels.ClosedByInterruptException;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.hdfs.client.HdfsClientConfigKeys;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
@@ -32,6 +33,8 @@
 import org.apache.hadoop.hdfs.server.datanode.SimulatedFSDataset;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.log4j.Level;
 import org.junit.Assert;
 
 import org.apache.hadoop.conf.Configuration;
@@ -39,10 +42,32 @@
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.DFSTestUtil.ShortCircuitTestContext;
+import org.junit.BeforeClass;
 import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
 
 public class TestRead {
-  final private int BLOCK_SIZE = 512;
+  static final private int BLOCK_SIZE = 512;
+  static final long SEED = 0xDEADBEEFL;
+  static final int FILE_SIZE = BLOCK_SIZE * 10;
+  private static final Logger LOG =
+      LoggerFactory.getLogger(TestRead.class.getName());
+  private final GenericTestUtils.LogCapturer dfsClientLog =
+      GenericTestUtils.LogCapturer.captureLogs(DFSClient.LOG);
+
+  @BeforeClass
+  public static void setLogLevel() {
+    GenericTestUtils.setLogLevel(DFSClient.LOG, Level.WARN);
+  }
 
   private void testEOF(MiniDFSCluster cluster, int fileLength) throws IOException {
     FileSystem fs = cluster.getFileSystem();
@@ -190,4 +215,126 @@ public boolean isSimulated() {
       }
     }
   }
+
+  /**
+   * Test logging in readBuffer() when the number of IOExceptions can be recovered by retrying on
+   * a different datanode or by refreshing data nodes and retrying each data node one more time.
+   */
+  @Test(timeout=120000)
+  public void testReadBufferIOExceptionLogging() throws IOException {
+    testReadBufferIOExceptionLogging(0, 0);
+    testReadBufferIOExceptionLogging(1, 0);
+    testReadBufferIOExceptionLogging(2, 0);
+    testReadBufferIOExceptionLogging(3, 0);
+    testReadBufferIOExceptionLogging(4, 1);
+    testReadBufferIOExceptionLogging(5, 1);
+    testReadBufferIOExceptionLogging(6, 1);
+  }
+
+  /**
+   * @param ioExceptions number of IOExceptions to throw during a test.
+   * @param maxBlockAcquireFailures number of refreshLocation we would perform once we mark
+   *                                   all current data nodes as dead.
+   */
+  private void testReadBufferIOExceptionLogging(final int ioExceptions,
+      int maxBlockAcquireFailures) throws IOException {
+    dfsClientLog.clearOutput();
+    Configuration conf = new Configuration();
+    conf.setInt(DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY, maxBlockAcquireFailures);
+    final int[] count = {0};
+    // Set up the InjectionHandler
+    DFSClientFaultInjector.set(Mockito.mock(DFSClientFaultInjector.class));
+    DFSClientFaultInjector injector = DFSClientFaultInjector.get();
+    Mockito.doAnswer(new Answer<Void>() {
+      @Override
+      public Void answer(InvocationOnMock invocation) throws Throwable {
+        if (count[0] < ioExceptions) {
+          LOG.info("-------------- throw IOException");
+          count[0]++;
+          throw new IOException("IOException test");
+        }
+        return null;
+      }
+    }).when(injector).fetchFromDatanodeException();
+
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).format(true).build();
+    DistributedFileSystem fileSys = cluster.getFileSystem();
+    DFSClient dfsClient = fileSys.getClient();
+    DFSInputStream input = null;
+    Path file = new Path("/testfile.dat");
+
+    try {
+      DFSTestUtil.createFile(fileSys, file, FILE_SIZE, FILE_SIZE, BLOCK_SIZE, (short) 3, SEED);
+
+      byte[] buffer = new byte[FILE_SIZE];
+      input = dfsClient.open(file.toString());
+      input.read(buffer, 0, FILE_SIZE);
+      assertEquals(ioExceptions, StringUtils.countMatches(dfsClientLog.getOutput(),
+          "Retry with the current or next available datanode."));
+    } finally {
+      Mockito.reset(injector);
+      IOUtils.cleanupWithLogger(LOG, input);
+      fileSys.close();
+      cluster.shutdown();
+      dfsClientLog.clearOutput();
+    }
+  }
+
+  /**
+   * Test the case where we always hit IOExceptions, causing the read request to fail.
+   */
+  @Test(timeout=60000)
+  public void testReadBufferIOExceptionLoggingFailedRequest() throws IOException {
+    testReadBufferIOExceptionLoggingFailedRequest(0);
+    testReadBufferIOExceptionLoggingFailedRequest(1);
+  }
+
+  private void testReadBufferIOExceptionLoggingFailedRequest(int maxBlockAcquireFailures)
+      throws IOException {
+    dfsClientLog.clearOutput();
+    Configuration conf = new Configuration();
+    conf.setInt(DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_KEY, maxBlockAcquireFailures);
+    // Set up the InjectionHandler
+    DFSClientFaultInjector.set(Mockito.mock(DFSClientFaultInjector.class));
+    DFSClientFaultInjector injector = DFSClientFaultInjector.get();
+    Mockito.doAnswer(new Answer<Void>() {
+      @Override
+      public Void answer(InvocationOnMock invocation) throws Throwable {
+        LOG.info("-------------- throw IOException");
+        throw new IOException("IOException test");
+      }
+    }).when(injector).fetchFromDatanodeException();
+
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).format(true).build();
+    DistributedFileSystem fileSys = cluster.getFileSystem();
+    DFSClient dfsClient = fileSys.getClient();
+    DFSInputStream input = null;
+    Path file = new Path("/testfile.dat");
+
+    try {
+      DFSTestUtil.createFile(fileSys, file, FILE_SIZE, FILE_SIZE, BLOCK_SIZE, (short) 3, SEED);
+
+      byte[] buffer = new byte[FILE_SIZE];
+      input = dfsClient.open(file.toString());
+      input.read(buffer, 0, FILE_SIZE);
+      fail();
+    } catch (BlockMissingException e) {
+      // Logging from readWithStrategy()
+      assertEquals(1, StringUtils.countMatches(dfsClientLog.getOutput(),
+          "Failed to read from all available datanodes for file"));
+      assertEquals(1 + 3L * (maxBlockAcquireFailures + 1),
+          StringUtils.countMatches(dfsClientLog.getOutput(),
+              "Exception when fetching file /testfile.dat at position="));
+      // Logging from actualGetFromOneDataNode
+      assertEquals(1 + 3L * (maxBlockAcquireFailures + 1),
+          StringUtils.countMatches(dfsClientLog.getOutput(),
+              "Retry with the current or next available datanode."));
+    } finally {
+      Mockito.reset(injector);
+      IOUtils.cleanupWithLogger(LOG, input);
+      fileSys.close();
+      cluster.shutdown();
+      dfsClientLog.clearOutput();
+    }
+  }
 }