hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestPread.java - hadoop-common - Git at Google

 /**
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you under the Apache License, Version 2.0 (the
  * "License"); you may not use this file except in compliance
  * with the License.  You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.apache.hadoop.hdfs;

 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;

 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Random;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;

 import org.apache.commons.logging.impl.Log4JLogger;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.ChecksumException;
 import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FSDataOutputStream;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtocol;
 import org.apache.hadoop.hdfs.server.datanode.SimulatedFSDataset;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.log4j.Level;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.Mockito;
 import org.mockito.invocation.InvocationOnMock;
 import org.mockito.stubbing.Answer;

 /**
  * This class tests the DFS positional read functionality in a single node
  * mini-cluster.
  */
 public class TestPread {
   static final long seed = 0xDEADBEEFL;
   static final int blockSize = 4096;
   boolean simulatedStorage;
   boolean isHedgedRead;

   @Before
   public void setup() {
     simulatedStorage = false;
     isHedgedRead = false;
   }

   private void writeFile(FileSystem fileSys, Path name) throws IOException {
     int replication = 3;// We need > 1 blocks to test out the hedged reads.
     // test empty file open and read
     DFSTestUtil.createFile(fileSys, name, 12 * blockSize, 0,
       blockSize, (short)replication, seed);
     FSDataInputStream in = fileSys.open(name);
     byte[] buffer = new byte[12 * blockSize];
     in.readFully(0, buffer, 0, 0);
     IOException res = null;
     try { // read beyond the end of the file
       in.readFully(0, buffer, 0, 1);
     } catch (IOException e) {
       // should throw an exception
       res = e;
     }
     assertTrue("Error reading beyond file boundary.", res != null);
     in.close();
     if (!fileSys.delete(name, true))
       assertTrue("Cannot delete file", false);

     // now create the real file
     DFSTestUtil.createFile(fileSys, name, 12 * blockSize, 12 * blockSize,
         blockSize, (short) replication, seed);
   }

   private void checkAndEraseData(byte[] actual, int from, byte[] expected, String message) {
     for (int idx = 0; idx < actual.length; idx++) {
       assertEquals(message+" byte "+(from+idx)+" differs. expected "+
                         expected[from+idx]+" actual "+actual[idx],
                         actual[idx], expected[from+idx]);
       actual[idx] = 0;
     }
   }

   private void doPread(FSDataInputStream stm, long position, byte[] buffer,
                        int offset, int length) throws IOException {
     int nread = 0;
     long totalRead = 0;
     DFSInputStream dfstm = null;

     if (stm.getWrappedStream() instanceof DFSInputStream) {
       dfstm = (DFSInputStream) (stm.getWrappedStream());
       totalRead = dfstm.getReadStatistics().getTotalBytesRead();
     }

     while (nread < length) {
       int nbytes =
           stm.read(position + nread, buffer, offset + nread, length - nread);
       assertTrue("Error in pread", nbytes > 0);
       nread += nbytes;
     }

     if (dfstm != null) {
       if (isHedgedRead) {
         assertTrue("Expected read statistic to be incremented", length <= dfstm
             .getReadStatistics().getTotalBytesRead() - totalRead);
       } else {
         assertEquals("Expected read statistic to be incremented", length, dfstm
             .getReadStatistics().getTotalBytesRead() - totalRead);
       }
     }
   }

   private void pReadFile(FileSystem fileSys, Path name) throws IOException {
     FSDataInputStream stm = fileSys.open(name);
     byte[] expected = new byte[12 * blockSize];
     if (simulatedStorage) {
       for (int i= 0; i < expected.length; i++) {
         expected[i] = SimulatedFSDataset.DEFAULT_DATABYTE;
       }
     } else {
       Random rand = new Random(seed);
       rand.nextBytes(expected);
     }
     // do a sanity check. Read first 4K bytes
     byte[] actual = new byte[4096];
     stm.readFully(actual);
     checkAndEraseData(actual, 0, expected, "Read Sanity Test");
     // now do a pread for the first 8K bytes
     actual = new byte[8192];
     doPread(stm, 0L, actual, 0, 8192);
     checkAndEraseData(actual, 0, expected, "Pread Test 1");
     // Now check to see if the normal read returns 4K-8K byte range
     actual = new byte[4096];
     stm.readFully(actual);
     checkAndEraseData(actual, 4096, expected, "Pread Test 2");
     // Now see if we can cross a single block boundary successfully
     // read 4K bytes from blockSize - 2K offset
     stm.readFully(blockSize - 2048, actual, 0, 4096);
     checkAndEraseData(actual, (blockSize - 2048), expected, "Pread Test 3");
     // now see if we can cross two block boundaries successfully
     // read blockSize + 4K bytes from blockSize - 2K offset
     actual = new byte[blockSize + 4096];
     stm.readFully(blockSize - 2048, actual);
     checkAndEraseData(actual, (blockSize - 2048), expected, "Pread Test 4");
     // now see if we can cross two block boundaries that are not cached
     // read blockSize + 4K bytes from 10*blockSize - 2K offset
     actual = new byte[blockSize + 4096];
     stm.readFully(10 * blockSize - 2048, actual);
     checkAndEraseData(actual, (10 * blockSize - 2048), expected, "Pread Test 5");
     // now check that even after all these preads, we can still read
     // bytes 8K-12K
     actual = new byte[4096];
     stm.readFully(actual);
     checkAndEraseData(actual, 8192, expected, "Pread Test 6");
     // done
     stm.close();
     // check block location caching
     stm = fileSys.open(name);
     stm.readFully(1, actual, 0, 4096);
     stm.readFully(4*blockSize, actual, 0, 4096);
     stm.readFully(7*blockSize, actual, 0, 4096);
     actual = new byte[3*4096];
     stm.readFully(0*blockSize, actual, 0, 3*4096);
     checkAndEraseData(actual, 0, expected, "Pread Test 7");
     actual = new byte[8*4096];
     stm.readFully(3*blockSize, actual, 0, 8*4096);
     checkAndEraseData(actual, 3*blockSize, expected, "Pread Test 8");
     // read the tail
     stm.readFully(11*blockSize+blockSize/2, actual, 0, blockSize/2);
     IOException res = null;
     try { // read beyond the end of the file
       stm.readFully(11*blockSize+blockSize/2, actual, 0, blockSize);
     } catch (IOException e) {
       // should throw an exception
       res = e;
     }
     assertTrue("Error reading beyond file boundary.", res != null);

     stm.close();
   }

   // test pread can survive datanode restarts
   private void datanodeRestartTest(MiniDFSCluster cluster, FileSystem fileSys,
       Path name) throws IOException {
     // skip this test if using simulated storage since simulated blocks
     // don't survive datanode restarts.
     if (simulatedStorage) {
       return;
     }
     int numBlocks = 1;
     assertTrue(numBlocks <= DFSConfigKeys.DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_DEFAULT);
     byte[] expected = new byte[numBlocks * blockSize];
     Random rand = new Random(seed);
     rand.nextBytes(expected);
     byte[] actual = new byte[numBlocks * blockSize];
     FSDataInputStream stm = fileSys.open(name);
     // read a block and get block locations cached as a result
     stm.readFully(0, actual);
     checkAndEraseData(actual, 0, expected, "Pread Datanode Restart Setup");
     // restart all datanodes. it is expected that they will
     // restart on different ports, hence, cached block locations
     // will no longer work.
     assertTrue(cluster.restartDataNodes());
     cluster.waitActive();
     // verify the block can be read again using the same InputStream
     // (via re-fetching of block locations from namenode). there is a
     // 3 sec sleep in chooseDataNode(), which can be shortened for
     // this test if configurable.
     stm.readFully(0, actual);
     checkAndEraseData(actual, 0, expected, "Pread Datanode Restart Test");
   }

   private void cleanupFile(FileSystem fileSys, Path name) throws IOException {
     assertTrue(fileSys.exists(name));
     assertTrue(fileSys.delete(name, true));
     assertTrue(!fileSys.exists(name));
   }

   private Callable<Void> getPReadFileCallable(final FileSystem fileSys,
       final Path file) {
     return new Callable<Void>() {
       public Void call() throws IOException {
         pReadFile(fileSys, file);
         return null;
       }
     };
   }

   /**
    * Tests positional read in DFS.
    */
   @Test
   public void testPreadDFS() throws IOException {
     Configuration conf = new Configuration();
     dfsPreadTest(conf, false, true); // normal pread
     dfsPreadTest(conf, true, true); // trigger read code path without
                                     // transferTo.
   }

   @Test
   public void testPreadDFSNoChecksum() throws IOException {
     Configuration conf = new Configuration();
     ((Log4JLogger)DataTransferProtocol.LOG).getLogger().setLevel(Level.ALL);
     dfsPreadTest(conf, false, false);
     dfsPreadTest(conf, true, false);
   }

   /**
    * Tests positional read in DFS, with hedged reads enabled.
    */
   @Test
   public void testHedgedPreadDFSBasic() throws IOException {
     isHedgedRead = true;
     Configuration conf = new Configuration();
     conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE, 5);
     conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS, 1);
     dfsPreadTest(conf, false, true); // normal pread
     dfsPreadTest(conf, true, true); // trigger read code path without
                                     // transferTo.
   }

   @Test
   public void testHedgedReadLoopTooManyTimes() throws IOException {
     Configuration conf = new Configuration();
     int numHedgedReadPoolThreads = 5;
     final int hedgedReadTimeoutMillis = 50;

     conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE,
         numHedgedReadPoolThreads);
     conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS,
         hedgedReadTimeoutMillis);
     conf.setInt(DFSConfigKeys.DFS_CLIENT_RETRY_WINDOW_BASE, 0);
     // Set up the InjectionHandler
     DFSClientFaultInjector.instance = Mockito
         .mock(DFSClientFaultInjector.class);
     DFSClientFaultInjector injector = DFSClientFaultInjector.instance;
     final int sleepMs = 100;
     Mockito.doAnswer(new Answer<Void>() {
       @Override
       public Void answer(InvocationOnMock invocation) throws Throwable {
         if (true) {
           Thread.sleep(hedgedReadTimeoutMillis + sleepMs);
           if (DFSClientFaultInjector.exceptionNum.compareAndSet(0, 1)) {
             System.out.println("-------------- throw Checksum Exception");
             throw new ChecksumException("ChecksumException test", 100);
           }
         }
         return null;
       }
     }).when(injector).fetchFromDatanodeException();
     Mockito.doAnswer(new Answer<Void>() {
       @Override
       public Void answer(InvocationOnMock invocation) throws Throwable {
         if (true) {
           Thread.sleep(sleepMs * 2);
         }
         return null;
       }
     }).when(injector).readFromDatanodeDelay();

     MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(2)
         .format(true).build();
     DistributedFileSystem fileSys = cluster.getFileSystem();
     DFSClient dfsClient = fileSys.getClient();
     FSDataOutputStream output = null;
     DFSInputStream input = null;
     String filename = "/hedgedReadMaxOut.dat";
     try {

       Path file = new Path(filename);
       output = fileSys.create(file, (short) 2);
       byte[] data = new byte[64 * 1024];
       output.write(data);
       output.flush();
       output.write(data);
       output.flush();
       output.write(data);
       output.flush();
       output.close();
       byte[] buffer = new byte[64 * 1024];
       input = dfsClient.open(filename);
       input.read(0, buffer, 0, 1024);
       input.close();
       assertEquals(3, input.getHedgedReadOpsLoopNumForTesting());
     } catch (BlockMissingException e) {
       assertTrue(false);
     } finally {
       Mockito.reset(injector);
       IOUtils.cleanup(null, input);
       IOUtils.cleanup(null, output);
       fileSys.close();
       cluster.shutdown();
     }
   }

   @Test
   public void testMaxOutHedgedReadPool() throws IOException,
       InterruptedException, ExecutionException {
     isHedgedRead = true;
     Configuration conf = new Configuration();
     int numHedgedReadPoolThreads = 5;
     final int initialHedgedReadTimeoutMillis = 50000;
     final int fixedSleepIntervalMillis = 50;
     conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE,
         numHedgedReadPoolThreads);
     conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS,
         initialHedgedReadTimeoutMillis);

     // Set up the InjectionHandler
     DFSClientFaultInjector.instance = Mockito
         .mock(DFSClientFaultInjector.class);
     DFSClientFaultInjector injector = DFSClientFaultInjector.instance;
     // make preads sleep for 50ms
     Mockito.doAnswer(new Answer<Void>() {
       @Override
       public Void answer(InvocationOnMock invocation) throws Throwable {
         Thread.sleep(fixedSleepIntervalMillis);
         return null;
       }
     }).when(injector).startFetchFromDatanode();

     MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3)
         .format(true).build();
     DistributedFileSystem fileSys = cluster.getFileSystem();
     DFSClient dfsClient = fileSys.getClient();
     DFSHedgedReadMetrics metrics = dfsClient.getHedgedReadMetrics();
     // Metrics instance is static, so we need to reset counts from prior tests.
     metrics.hedgedReadOps.set(0);
     metrics.hedgedReadOpsWin.set(0);
     metrics.hedgedReadOpsInCurThread.set(0);

     try {
       Path file1 = new Path("hedgedReadMaxOut.dat");
       writeFile(fileSys, file1);
       // Basic test. Reads complete within timeout. Assert that there were no
       // hedged reads.
       pReadFile(fileSys, file1);
       // assert that there were no hedged reads. 50ms + delta < 500ms
       assertTrue(metrics.getHedgedReadOps() == 0);
       assertTrue(metrics.getHedgedReadOpsInCurThread() == 0);
       /*
        * Reads take longer than timeout. But, only one thread reading. Assert
        * that there were hedged reads. But, none of the reads had to run in the
        * current thread.
        */
       dfsClient.setHedgedReadTimeout(50); // 50ms
       pReadFile(fileSys, file1);
       // assert that there were hedged reads
       assertTrue(metrics.getHedgedReadOps() > 0);
       assertTrue(metrics.getHedgedReadOpsInCurThread() == 0);
       /*
        * Multiple threads reading. Reads take longer than timeout. Assert that
        * there were hedged reads. And that reads had to run in the current
        * thread.
        */
       int factor = 10;
       int numHedgedReads = numHedgedReadPoolThreads * factor;
       long initialReadOpsValue = metrics.getHedgedReadOps();
       ExecutorService executor = Executors.newFixedThreadPool(numHedgedReads);
       ArrayList<Future<Void>> futures = new ArrayList<Future<Void>>();
       for (int i = 0; i < numHedgedReads; i++) {
         futures.add(executor.submit(getPReadFileCallable(fileSys, file1)));
       }
       for (int i = 0; i < numHedgedReads; i++) {
         futures.get(i).get();
       }
       assertTrue(metrics.getHedgedReadOps() > initialReadOpsValue);
       assertTrue(metrics.getHedgedReadOpsInCurThread() > 0);
       cleanupFile(fileSys, file1);
       executor.shutdown();
     } finally {
       fileSys.close();
       cluster.shutdown();
       Mockito.reset(injector);
     }
   }

   private void dfsPreadTest(Configuration conf, boolean disableTransferTo, boolean verifyChecksum)
       throws IOException {
     conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, 4096);
     conf.setLong(DFSConfigKeys.DFS_CLIENT_READ_PREFETCH_SIZE_KEY, 4096);
     // Set short retry timeouts so this test runs faster
     conf.setInt(DFSConfigKeys.DFS_CLIENT_RETRY_WINDOW_BASE, 0);
     if (simulatedStorage) {
       SimulatedFSDataset.setFactory(conf);
     }
     if (disableTransferTo) {
       conf.setBoolean("dfs.datanode.transferTo.allowed", false);
     }
     MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).build();
     FileSystem fileSys = cluster.getFileSystem();
     fileSys.setVerifyChecksum(verifyChecksum);
     try {
       Path file1 = new Path("preadtest.dat");
       writeFile(fileSys, file1);
       pReadFile(fileSys, file1);
       datanodeRestartTest(cluster, fileSys, file1);
       cleanupFile(fileSys, file1);
     } finally {
       fileSys.close();
       cluster.shutdown();
     }
   }

   @Test
   public void testPreadDFSSimulated() throws IOException {
     simulatedStorage = true;
     testPreadDFS();
   }

   /**
    * Tests positional read in LocalFS.
    */
   @Test
   public void testPreadLocalFS() throws IOException {
     Configuration conf = new HdfsConfiguration();
     FileSystem fileSys = FileSystem.getLocal(conf);
     try {
       Path file1 = new Path("build/test/data", "preadtest.dat");
       writeFile(fileSys, file1);
       pReadFile(fileSys, file1);
       cleanupFile(fileSys, file1);
     } finally {
       fileSys.close();
     }
   }

   public static void main(String[] args) throws Exception {
     new TestPread().testPreadDFS();
   }
 }
	/**
	* Licensed to the Apache Software Foundation (ASF) under one
	* or more contributor license agreements. See the NOTICE file
	* distributed with this work for additional information
	* regarding copyright ownership. The ASF licenses this file
	* to you under the Apache License, Version 2.0 (the
	* "License"); you may not use this file except in compliance
	* with the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.hadoop.hdfs;

	import static org.junit.Assert.assertEquals;
	import static org.junit.Assert.assertTrue;

	import java.io.IOException;
	import java.util.ArrayList;
	import java.util.Random;
	import java.util.concurrent.Callable;
	import java.util.concurrent.ExecutionException;
	import java.util.concurrent.ExecutorService;
	import java.util.concurrent.Executors;
	import java.util.concurrent.Future;

	import org.apache.commons.logging.impl.Log4JLogger;
	import org.apache.hadoop.conf.Configuration;
	import org.apache.hadoop.fs.ChecksumException;
	import org.apache.hadoop.fs.FSDataInputStream;
	import org.apache.hadoop.fs.FSDataOutputStream;
	import org.apache.hadoop.fs.FileSystem;
	import org.apache.hadoop.fs.Path;
	import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtocol;
	import org.apache.hadoop.hdfs.server.datanode.SimulatedFSDataset;
	import org.apache.hadoop.io.IOUtils;
	import org.apache.log4j.Level;
	import org.junit.Before;
	import org.junit.Test;
	import org.mockito.Mockito;
	import org.mockito.invocation.InvocationOnMock;
	import org.mockito.stubbing.Answer;

	/**
	* This class tests the DFS positional read functionality in a single node
	* mini-cluster.
	*/
	public class TestPread {
	static final long seed = 0xDEADBEEFL;
	static final int blockSize = 4096;
	boolean simulatedStorage;
	boolean isHedgedRead;

	@Before
	public void setup() {
	simulatedStorage = false;
	isHedgedRead = false;
	}

	private void writeFile(FileSystem fileSys, Path name) throws IOException {
	int replication = 3;// We need > 1 blocks to test out the hedged reads.
	// test empty file open and read
	DFSTestUtil.createFile(fileSys, name, 12 * blockSize, 0,
	blockSize, (short)replication, seed);
	FSDataInputStream in = fileSys.open(name);
	byte[] buffer = new byte[12 * blockSize];
	in.readFully(0, buffer, 0, 0);
	IOException res = null;
	try { // read beyond the end of the file
	in.readFully(0, buffer, 0, 1);
	} catch (IOException e) {
	// should throw an exception
	res = e;
	}
	assertTrue("Error reading beyond file boundary.", res != null);
	in.close();
	if (!fileSys.delete(name, true))
	assertTrue("Cannot delete file", false);

	// now create the real file
	DFSTestUtil.createFile(fileSys, name, 12 * blockSize, 12 * blockSize,
	blockSize, (short) replication, seed);
	}

	private void checkAndEraseData(byte[] actual, int from, byte[] expected, String message) {
	for (int idx = 0; idx < actual.length; idx++) {
	assertEquals(message+" byte "+(from+idx)+" differs. expected "+
	expected[from+idx]+" actual "+actual[idx],
	actual[idx], expected[from+idx]);
	actual[idx] = 0;
	}
	}

	private void doPread(FSDataInputStream stm, long position, byte[] buffer,
	int offset, int length) throws IOException {
	int nread = 0;
	long totalRead = 0;
	DFSInputStream dfstm = null;

	if (stm.getWrappedStream() instanceof DFSInputStream) {
	dfstm = (DFSInputStream) (stm.getWrappedStream());
	totalRead = dfstm.getReadStatistics().getTotalBytesRead();
	}

	while (nread < length) {
	int nbytes =
	stm.read(position + nread, buffer, offset + nread, length - nread);
	assertTrue("Error in pread", nbytes > 0);
	nread += nbytes;
	}

	if (dfstm != null) {
	if (isHedgedRead) {
	assertTrue("Expected read statistic to be incremented", length <= dfstm
	.getReadStatistics().getTotalBytesRead() - totalRead);
	} else {
	assertEquals("Expected read statistic to be incremented", length, dfstm
	.getReadStatistics().getTotalBytesRead() - totalRead);
	}
	}
	}

	private void pReadFile(FileSystem fileSys, Path name) throws IOException {
	FSDataInputStream stm = fileSys.open(name);
	byte[] expected = new byte[12 * blockSize];
	if (simulatedStorage) {
	for (int i= 0; i < expected.length; i++) {
	expected[i] = SimulatedFSDataset.DEFAULT_DATABYTE;
	}
	} else {
	Random rand = new Random(seed);
	rand.nextBytes(expected);
	}
	// do a sanity check. Read first 4K bytes
	byte[] actual = new byte[4096];
	stm.readFully(actual);
	checkAndEraseData(actual, 0, expected, "Read Sanity Test");
	// now do a pread for the first 8K bytes
	actual = new byte[8192];
	doPread(stm, 0L, actual, 0, 8192);
	checkAndEraseData(actual, 0, expected, "Pread Test 1");
	// Now check to see if the normal read returns 4K-8K byte range
	actual = new byte[4096];
	stm.readFully(actual);
	checkAndEraseData(actual, 4096, expected, "Pread Test 2");
	// Now see if we can cross a single block boundary successfully
	// read 4K bytes from blockSize - 2K offset
	stm.readFully(blockSize - 2048, actual, 0, 4096);
	checkAndEraseData(actual, (blockSize - 2048), expected, "Pread Test 3");
	// now see if we can cross two block boundaries successfully
	// read blockSize + 4K bytes from blockSize - 2K offset
	actual = new byte[blockSize + 4096];
	stm.readFully(blockSize - 2048, actual);
	checkAndEraseData(actual, (blockSize - 2048), expected, "Pread Test 4");
	// now see if we can cross two block boundaries that are not cached
	// read blockSize + 4K bytes from 10*blockSize - 2K offset
	actual = new byte[blockSize + 4096];
	stm.readFully(10 * blockSize - 2048, actual);
	checkAndEraseData(actual, (10 * blockSize - 2048), expected, "Pread Test 5");
	// now check that even after all these preads, we can still read
	// bytes 8K-12K
	actual = new byte[4096];
	stm.readFully(actual);
	checkAndEraseData(actual, 8192, expected, "Pread Test 6");
	// done
	stm.close();
	// check block location caching
	stm = fileSys.open(name);
	stm.readFully(1, actual, 0, 4096);
	stm.readFully(4*blockSize, actual, 0, 4096);
	stm.readFully(7*blockSize, actual, 0, 4096);
	actual = new byte[3*4096];
	stm.readFully(0blockSize, actual, 0, 34096);
	checkAndEraseData(actual, 0, expected, "Pread Test 7");
	actual = new byte[8*4096];
	stm.readFully(3blockSize, actual, 0, 84096);
	checkAndEraseData(actual, 3*blockSize, expected, "Pread Test 8");
	// read the tail
	stm.readFully(11*blockSize+blockSize/2, actual, 0, blockSize/2);
	IOException res = null;
	try { // read beyond the end of the file
	stm.readFully(11*blockSize+blockSize/2, actual, 0, blockSize);
	} catch (IOException e) {
	// should throw an exception
	res = e;
	}
	assertTrue("Error reading beyond file boundary.", res != null);

	stm.close();
	}

	// test pread can survive datanode restarts
	private void datanodeRestartTest(MiniDFSCluster cluster, FileSystem fileSys,
	Path name) throws IOException {
	// skip this test if using simulated storage since simulated blocks
	// don't survive datanode restarts.
	if (simulatedStorage) {
	return;
	}
	int numBlocks = 1;
	assertTrue(numBlocks <= DFSConfigKeys.DFS_CLIENT_MAX_BLOCK_ACQUIRE_FAILURES_DEFAULT);
	byte[] expected = new byte[numBlocks * blockSize];
	Random rand = new Random(seed);
	rand.nextBytes(expected);
	byte[] actual = new byte[numBlocks * blockSize];
	FSDataInputStream stm = fileSys.open(name);
	// read a block and get block locations cached as a result
	stm.readFully(0, actual);
	checkAndEraseData(actual, 0, expected, "Pread Datanode Restart Setup");
	// restart all datanodes. it is expected that they will
	// restart on different ports, hence, cached block locations
	// will no longer work.
	assertTrue(cluster.restartDataNodes());
	cluster.waitActive();
	// verify the block can be read again using the same InputStream
	// (via re-fetching of block locations from namenode). there is a
	// 3 sec sleep in chooseDataNode(), which can be shortened for
	// this test if configurable.
	stm.readFully(0, actual);
	checkAndEraseData(actual, 0, expected, "Pread Datanode Restart Test");
	}

	private void cleanupFile(FileSystem fileSys, Path name) throws IOException {
	assertTrue(fileSys.exists(name));
	assertTrue(fileSys.delete(name, true));
	assertTrue(!fileSys.exists(name));
	}

	private Callable<Void> getPReadFileCallable(final FileSystem fileSys,
	final Path file) {
	return new Callable<Void>() {
	public Void call() throws IOException {
	pReadFile(fileSys, file);
	return null;
	}
	};
	}

	/**
	* Tests positional read in DFS.
	*/
	@Test
	public void testPreadDFS() throws IOException {
	Configuration conf = new Configuration();
	dfsPreadTest(conf, false, true); // normal pread
	dfsPreadTest(conf, true, true); // trigger read code path without
	// transferTo.
	}

	@Test
	public void testPreadDFSNoChecksum() throws IOException {
	Configuration conf = new Configuration();
	((Log4JLogger)DataTransferProtocol.LOG).getLogger().setLevel(Level.ALL);
	dfsPreadTest(conf, false, false);
	dfsPreadTest(conf, true, false);
	}

	/**
	* Tests positional read in DFS, with hedged reads enabled.
	*/
	@Test
	public void testHedgedPreadDFSBasic() throws IOException {
	isHedgedRead = true;
	Configuration conf = new Configuration();
	conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE, 5);
	conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS, 1);
	dfsPreadTest(conf, false, true); // normal pread
	dfsPreadTest(conf, true, true); // trigger read code path without
	// transferTo.
	}

	@Test
	public void testHedgedReadLoopTooManyTimes() throws IOException {
	Configuration conf = new Configuration();
	int numHedgedReadPoolThreads = 5;
	final int hedgedReadTimeoutMillis = 50;

	conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE,
	numHedgedReadPoolThreads);
	conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS,
	hedgedReadTimeoutMillis);
	conf.setInt(DFSConfigKeys.DFS_CLIENT_RETRY_WINDOW_BASE, 0);
	// Set up the InjectionHandler
	DFSClientFaultInjector.instance = Mockito
	.mock(DFSClientFaultInjector.class);
	DFSClientFaultInjector injector = DFSClientFaultInjector.instance;
	final int sleepMs = 100;
	Mockito.doAnswer(new Answer<Void>() {
	@Override
	public Void answer(InvocationOnMock invocation) throws Throwable {
	if (true) {
	Thread.sleep(hedgedReadTimeoutMillis + sleepMs);
	if (DFSClientFaultInjector.exceptionNum.compareAndSet(0, 1)) {
	System.out.println("-------------- throw Checksum Exception");
	throw new ChecksumException("ChecksumException test", 100);
	}
	}
	return null;
	}
	}).when(injector).fetchFromDatanodeException();
	Mockito.doAnswer(new Answer<Void>() {
	@Override
	public Void answer(InvocationOnMock invocation) throws Throwable {
	if (true) {
	Thread.sleep(sleepMs * 2);
	}
	return null;
	}
	}).when(injector).readFromDatanodeDelay();

	MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(2)
	.format(true).build();
	DistributedFileSystem fileSys = cluster.getFileSystem();
	DFSClient dfsClient = fileSys.getClient();
	FSDataOutputStream output = null;
	DFSInputStream input = null;
	String filename = "/hedgedReadMaxOut.dat";
	try {

	Path file = new Path(filename);
	output = fileSys.create(file, (short) 2);
	byte[] data = new byte[64 * 1024];
	output.write(data);
	output.flush();
	output.write(data);
	output.flush();
	output.write(data);
	output.flush();
	output.close();
	byte[] buffer = new byte[64 * 1024];
	input = dfsClient.open(filename);
	input.read(0, buffer, 0, 1024);
	input.close();
	assertEquals(3, input.getHedgedReadOpsLoopNumForTesting());
	} catch (BlockMissingException e) {
	assertTrue(false);
	} finally {
	Mockito.reset(injector);
	IOUtils.cleanup(null, input);
	IOUtils.cleanup(null, output);
	fileSys.close();
	cluster.shutdown();
	}
	}

	@Test
	public void testMaxOutHedgedReadPool() throws IOException,
	InterruptedException, ExecutionException {
	isHedgedRead = true;
	Configuration conf = new Configuration();
	int numHedgedReadPoolThreads = 5;
	final int initialHedgedReadTimeoutMillis = 50000;
	final int fixedSleepIntervalMillis = 50;
	conf.setInt(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE,
	numHedgedReadPoolThreads);
	conf.setLong(DFSConfigKeys.DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS,
	initialHedgedReadTimeoutMillis);

	// Set up the InjectionHandler
	DFSClientFaultInjector.instance = Mockito
	.mock(DFSClientFaultInjector.class);
	DFSClientFaultInjector injector = DFSClientFaultInjector.instance;
	// make preads sleep for 50ms
	Mockito.doAnswer(new Answer<Void>() {
	@Override
	public Void answer(InvocationOnMock invocation) throws Throwable {
	Thread.sleep(fixedSleepIntervalMillis);
	return null;
	}
	}).when(injector).startFetchFromDatanode();

	MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3)
	.format(true).build();
	DistributedFileSystem fileSys = cluster.getFileSystem();
	DFSClient dfsClient = fileSys.getClient();
	DFSHedgedReadMetrics metrics = dfsClient.getHedgedReadMetrics();
	// Metrics instance is static, so we need to reset counts from prior tests.
	metrics.hedgedReadOps.set(0);
	metrics.hedgedReadOpsWin.set(0);
	metrics.hedgedReadOpsInCurThread.set(0);

	try {
	Path file1 = new Path("hedgedReadMaxOut.dat");
	writeFile(fileSys, file1);
	// Basic test. Reads complete within timeout. Assert that there were no
	// hedged reads.
	pReadFile(fileSys, file1);
	// assert that there were no hedged reads. 50ms + delta < 500ms
	assertTrue(metrics.getHedgedReadOps() == 0);
	assertTrue(metrics.getHedgedReadOpsInCurThread() == 0);
	/*
	* Reads take longer than timeout. But, only one thread reading. Assert
	* that there were hedged reads. But, none of the reads had to run in the
	* current thread.
	*/
	dfsClient.setHedgedReadTimeout(50); // 50ms
	pReadFile(fileSys, file1);
	// assert that there were hedged reads
	assertTrue(metrics.getHedgedReadOps() > 0);
	assertTrue(metrics.getHedgedReadOpsInCurThread() == 0);
	/*
	* Multiple threads reading. Reads take longer than timeout. Assert that
	* there were hedged reads. And that reads had to run in the current
	* thread.
	*/
	int factor = 10;
	int numHedgedReads = numHedgedReadPoolThreads * factor;
	long initialReadOpsValue = metrics.getHedgedReadOps();
	ExecutorService executor = Executors.newFixedThreadPool(numHedgedReads);
	ArrayList<Future<Void>> futures = new ArrayList<Future<Void>>();
	for (int i = 0; i < numHedgedReads; i++) {
	futures.add(executor.submit(getPReadFileCallable(fileSys, file1)));
	}
	for (int i = 0; i < numHedgedReads; i++) {
	futures.get(i).get();
	}
	assertTrue(metrics.getHedgedReadOps() > initialReadOpsValue);
	assertTrue(metrics.getHedgedReadOpsInCurThread() > 0);
	cleanupFile(fileSys, file1);
	executor.shutdown();
	} finally {
	fileSys.close();
	cluster.shutdown();
	Mockito.reset(injector);
	}
	}

	private void dfsPreadTest(Configuration conf, boolean disableTransferTo, boolean verifyChecksum)
	throws IOException {
	conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, 4096);
	conf.setLong(DFSConfigKeys.DFS_CLIENT_READ_PREFETCH_SIZE_KEY, 4096);
	// Set short retry timeouts so this test runs faster
	conf.setInt(DFSConfigKeys.DFS_CLIENT_RETRY_WINDOW_BASE, 0);
	if (simulatedStorage) {
	SimulatedFSDataset.setFactory(conf);
	}
	if (disableTransferTo) {
	conf.setBoolean("dfs.datanode.transferTo.allowed", false);
	}
	MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).build();
	FileSystem fileSys = cluster.getFileSystem();
	fileSys.setVerifyChecksum(verifyChecksum);
	try {
	Path file1 = new Path("preadtest.dat");
	writeFile(fileSys, file1);
	pReadFile(fileSys, file1);
	datanodeRestartTest(cluster, fileSys, file1);
	cleanupFile(fileSys, file1);
	} finally {
	fileSys.close();
	cluster.shutdown();
	}
	}

	@Test
	public void testPreadDFSSimulated() throws IOException {
	simulatedStorage = true;
	testPreadDFS();
	}

	/**
	* Tests positional read in LocalFS.
	*/
	@Test
	public void testPreadLocalFS() throws IOException {
	Configuration conf = new HdfsConfiguration();
	FileSystem fileSys = FileSystem.getLocal(conf);
	try {
	Path file1 = new Path("build/test/data", "preadtest.dat");
	writeFile(fileSys, file1);
	pReadFile(fileSys, file1);
	cleanupFile(fileSys, file1);
	} finally {
	fileSys.close();
	}
	}

	public static void main(String[] args) throws Exception {
	new TestPread().testPreadDFS();
	}
	}