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From t...@apache.org
Subject svn commit: r1099687 [4/15] - in /hadoop/hdfs/branches/HDFS-1073: ./ bin/ src/c++/libhdfs/ src/contrib/hdfsproxy/ src/contrib/hdfsproxy/src/java/org/apache/hadoop/hdfsproxy/ src/java/ src/java/org/apache/hadoop/hdfs/ src/java/org/apache/hadoop/hdfs/pro...
Date Thu, 05 May 2011 05:40:13 GMT
Modified: hadoop/hdfs/branches/HDFS-1073/src/java/org/apache/hadoop/hdfs/server/datanode/DataBlockScanner.java
URL: http://svn.apache.org/viewvc/hadoop/hdfs/branches/HDFS-1073/src/java/org/apache/hadoop/hdfs/server/datanode/DataBlockScanner.java?rev=1099687&r1=1099686&r2=1099687&view=diff
==============================================================================
--- hadoop/hdfs/branches/HDFS-1073/src/java/org/apache/hadoop/hdfs/server/datanode/DataBlockScanner.java
(original)
+++ hadoop/hdfs/branches/HDFS-1073/src/java/org/apache/hadoop/hdfs/server/datanode/DataBlockScanner.java
Thu May  5 05:40:07 2011
@@ -18,947 +18,279 @@
 
 package org.apache.hadoop.hdfs.server.datanode;
 
-import java.io.BufferedReader;
-import java.io.Closeable;
-import java.io.DataOutputStream;
 import java.io.File;
-import java.io.FileNotFoundException;
-import java.io.FileOutputStream;
-import java.io.FileReader;
 import java.io.IOException;
-import java.io.PrintStream;
-import java.text.DateFormat;
-import java.text.SimpleDateFormat;
-import java.util.Collections;
-import java.util.Date;
-import java.util.HashMap;
 import java.util.Iterator;
-import java.util.List;
-import java.util.Random;
-import java.util.TreeSet;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
+import java.util.TreeMap;
 
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.protocol.Block;
-import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
-import org.apache.hadoop.hdfs.protocol.LocatedBlock;
-import org.apache.hadoop.hdfs.server.common.GenerationStamp;
-import org.apache.hadoop.hdfs.util.DataTransferThrottler;
-import org.apache.hadoop.io.IOUtils;
-import org.apache.hadoop.util.StringUtils;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.server.datanode.DataNode.BPOfferService;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 
 /**
- * Performs two types of scanning:
- * <li> Gets block files from the data directories and reconciles the
- * difference between the blocks on the disk and in memory in
- * {@link FSDataset}</li>
- * <li> Scans the data directories for block files and verifies that
- * the files are not corrupt</li>
- * This keeps track of blocks and their last verification times.
- * Currently it does not modify the metadata for block.
+ * DataBlockScanner manages block scanning for all the block pools. For each
+ * block pool a {@link BlockPoolSliceScanner} is created which runs in a separate
+ * thread to scan the blocks for that block pool. When a {@link BPOfferService}
+ * becomes alive or dies, blockPoolScannerMap in this class is updated.
  */
-
-class DataBlockScanner implements Runnable {
-  
+@InterfaceAudience.Private
+public class DataBlockScanner implements Runnable {
   public static final Log LOG = LogFactory.getLog(DataBlockScanner.class);
+  private final DataNode datanode;
+  private final FSDataset dataset;
+  private final Configuration conf;
   
-  private static final int MAX_SCAN_RATE = 8 * 1024 * 1024; // 8MB per sec
-  private static final int MIN_SCAN_RATE = 1 * 1024 * 1024; // 1MB per sec
-  
-  static final long DEFAULT_SCAN_PERIOD_HOURS = 21*24L; // three weeks
-  private static final long ONE_DAY = 24*3600*1000L;
-  
-  static final DateFormat dateFormat = 
-                    new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,SSS");
-  
-  static final String verificationLogFile = "dncp_block_verification.log";
-  static final int verficationLogLimit = 5; // * numBlocks.
-
-  private long scanPeriod = DEFAULT_SCAN_PERIOD_HOURS * 3600 * 1000;
-  DataNode datanode;
-  FSDataset dataset;
-  
-  // sorted set
-  TreeSet<BlockScanInfo> blockInfoSet;
-  HashMap<Block, BlockScanInfo> blockMap;
-  
-  long totalScans = 0;
-  long totalVerifications = 0; // includes remote verification by clients.
-  long totalScanErrors = 0;
-  long totalTransientErrors = 0;
-  
-  long currentPeriodStart = System.currentTimeMillis();
-  long bytesLeft = 0; // Bytes to scan in this period
-  long totalBytesToScan = 0;
-  
-  private LogFileHandler verificationLog;
-  
-  Random random = new Random();
-  
-  DataTransferThrottler throttler = null;
-  
-  // Reconciles blocks on disk to blocks in memory
-  DirectoryScanner dirScanner;
-
-  private static enum ScanType {
-    REMOTE_READ,           // Verified when a block read by a client etc
-    VERIFICATION_SCAN,     // scanned as part of periodic verfication
-    NONE,
-  }
-  
-  static class BlockScanInfo implements Comparable<BlockScanInfo> {
-    Block block;
-    long lastScanTime = 0;
-    long lastLogTime = 0;
-    ScanType lastScanType = ScanType.NONE; 
-    boolean lastScanOk = true;
-    
-    BlockScanInfo(Block block) {
-      this.block = block;
-    }
-    
-    public int hashCode() {
-      return block.hashCode();
-    }
-    
-    public boolean equals(Object other) {
-      return other instanceof BlockScanInfo &&
-             compareTo((BlockScanInfo)other) == 0;
-    }
-    
-    long getLastScanTime() {
-      return ( lastScanType == ScanType.NONE) ? 0 : lastScanTime;
-    }
-    
-    public int compareTo(BlockScanInfo other) {
-      long t1 = lastScanTime;
-      long t2 = other.lastScanTime;
-      return ( t1 < t2 ) ? -1 : 
-                          (( t1 > t2 ) ? 1 : block.compareTo(other.block)); 
-    }
-  }
+  /**
+   * Map to find the BlockPoolScanner for a given block pool id. This is updated
+   * when a BPOfferService becomes alive or dies.
+   */
+  private final TreeMap<String, BlockPoolSliceScanner> blockPoolScannerMap = 
+    new TreeMap<String, BlockPoolSliceScanner>();
+  Thread blockScannerThread = null;
   
   DataBlockScanner(DataNode datanode, FSDataset dataset, Configuration conf) {
     this.datanode = datanode;
     this.dataset = dataset;
-    scanPeriod = conf.getInt(DFSConfigKeys.DFS_DATANODE_SCAN_PERIOD_HOURS_KEY, 
-                             DFSConfigKeys.DFS_DATANODE_SCAN_PERIOD_HOURS_DEFAULT);
-    if ( scanPeriod <= 0 ) {
-      scanPeriod = DEFAULT_SCAN_PERIOD_HOURS;
-    }
-    scanPeriod *= 3600 * 1000;
-    // initialized when the scanner thread is started.
-
-    dirScanner = new DirectoryScanner(dataset, conf);
+    this.conf = conf;
   }
   
-  private synchronized boolean isInitialized() {
-    return throttler != null;
-  }
-  
-  private void updateBytesToScan(long len, long lastScanTime) {
-    // len could be negative when a block is deleted.
-    totalBytesToScan += len;
-    if ( lastScanTime < currentPeriodStart ) {
-      bytesLeft += len;
-    }
-    // Should we change throttler bandwidth every time bytesLeft changes?
-    // not really required.
-  }
-  
-  private synchronized void addBlockInfo(BlockScanInfo info) {
-    boolean added = blockInfoSet.add(info);
-    blockMap.put(info.block, info);
-    
-    if ( added ) {
-      LogFileHandler log = verificationLog;
-      if (log != null) {
-        log.setMaxNumLines(blockMap.size() * verficationLogLimit);
+  public void run() {
+    String currentBpId = "";
+    boolean firstRun = true;
+    while (datanode.shouldRun && !Thread.interrupted()) {
+      //Sleep everytime except in the first interation.
+      if (!firstRun) {
+        try {
+          Thread.sleep(5000);
+        } catch (InterruptedException ex) {
+          // Interrupt itself again to set the interrupt status
+          blockScannerThread.interrupt();
+          continue;
+        }
+      } else {
+        firstRun = false;
       }
-      updateBytesToScan(info.block.getNumBytes(), info.lastScanTime);
-    }
-  }
-  
-  private synchronized void delBlockInfo(BlockScanInfo info) {
-    boolean exists = blockInfoSet.remove(info);
-    blockMap.remove(info.block);
-    if ( exists ) {
-      LogFileHandler log = verificationLog;
-      if (log != null) {
-        log.setMaxNumLines(blockMap.size() * verficationLogLimit);
+      
+      BlockPoolSliceScanner bpScanner = getNextBPScanner(currentBpId);
+      if (bpScanner == null) {
+        // Possible if thread is interrupted
+        continue;
       }
-      updateBytesToScan(-info.block.getNumBytes(), info.lastScanTime);
-    }
-  }
-  
-  /** Update blockMap by the given LogEntry */
-  private synchronized void updateBlockInfo(LogEntry e) {
-    BlockScanInfo info = blockMap.get(new Block(e.blockId, 0, e.genStamp));
-    
-    if(info != null && e.verificationTime > 0 && 
-        info.lastScanTime < e.verificationTime) {
-      delBlockInfo(info);
-      info.lastScanTime = e.verificationTime;
-      info.lastScanType = ScanType.VERIFICATION_SCAN;
-      addBlockInfo(info);
-    }
-  }
-
-  private void init() {
-    
-    // get the list of blocks and arrange them in random order
-    List<Block> arr = dataset.getFinalizedBlocks();
-    Collections.shuffle(arr);
-    
-    blockInfoSet = new TreeSet<BlockScanInfo>();
-    blockMap = new HashMap<Block, BlockScanInfo>();
-    
-    long scanTime = -1;
-    for (Block block : arr) {
-      BlockScanInfo info = new BlockScanInfo( block );
-      info.lastScanTime = scanTime--; 
-      //still keep 'info.lastScanType' to NONE.
-      addBlockInfo(info);
-    }
-
-    /* Pick the first directory that has any existing scanner log.
-     * otherwise, pick the first directory.
-     */
-    File dir = null;
-    FSDataset.FSVolume[] volumes = dataset.volumes.volumes;
-    for(FSDataset.FSVolume vol : volumes) {
-      if (LogFileHandler.isFilePresent(vol.getDir(), verificationLogFile)) {
-        dir = vol.getDir();
-        break;
+      currentBpId = bpScanner.getBlockPoolId();
+      // If BPOfferService for this pool is not alive, don't process it
+      if (!datanode.isBPServiceAlive(currentBpId)) {
+        LOG.warn("Block Pool " + currentBpId + " is not alive");
+        // Remove in case BP service died abruptly without proper shutdown
+        removeBlockPool(currentBpId);
+        continue;
       }
-    }
-    if (dir == null) {
-      dir = volumes[0].getDir();
-    }
-    
-    try {
-      // max lines will be updated later during initialization.
-      verificationLog = new LogFileHandler(dir, verificationLogFile, 100);
-    } catch (IOException e) {
-      LOG.warn("Could not open verfication log. " +
-               "Verification times are not stored.");
-    }
-    
-    synchronized (this) {
-      throttler = new DataTransferThrottler(200, MAX_SCAN_RATE);
+      bpScanner.scanBlockPoolSlice();
     }
   }
 
-  private synchronized long getNewBlockScanTime() {
-    /* If there are a lot of blocks, this returns a random time with in 
-     * the scan period. Otherwise something sooner.
-     */
-    long period = Math.min(scanPeriod, 
-                           Math.max(blockMap.size(),1) * 600 * 1000L);
-    return System.currentTimeMillis() - scanPeriod + 
-           random.nextInt((int)period);    
-  }
-
-  /** Adds block to list of blocks */
-  synchronized void addBlock(Block block) {
-    if (!isInitialized()) {
-      return;
-    }
+  // Wait for at least one block pool to be up
+  private void waitForInit(String bpid) {
+    UpgradeManagerDatanode um = null;
+    if(bpid != null && !bpid.equals(""))
+      um = DataNode.getUpgradeManagerDatanode(bpid);
     
-    BlockScanInfo info = blockMap.get(block);
-    if ( info != null ) {
-      LOG.warn("Adding an already existing block " + block);
-      delBlockInfo(info);
+    while ((um != null && ! um.isUpgradeCompleted())
+        || (getBlockPoolSetSize() < datanode.getAllBpOs().length)
+        || (getBlockPoolSetSize() < 1)) {
+      try {
+        Thread.sleep(5000);
+      } catch (InterruptedException e) {
+        blockScannerThread.interrupt();
+        return;
+      }
     }
-    
-    info = new BlockScanInfo(block);    
-    info.lastScanTime = getNewBlockScanTime();
-    
-    addBlockInfo(info);
-    adjustThrottler();
   }
   
-  /** Deletes the block from internal structures */
-  synchronized void deleteBlock(Block block) {
-    if (!isInitialized()) {
-      return;
-    }
-    BlockScanInfo info = blockMap.get(block);
-    if ( info != null ) {
-      delBlockInfo(info);
+  /**
+   * Find next block pool id to scan. There should be only one current
+   * verification log file. Find which block pool contains the current
+   * verification log file and that is used as the starting block pool id. If no
+   * current files are found start with first block-pool in the blockPoolSet.
+   * However, if more than one current files are found, the one with latest 
+   * modification time is used to find the next block pool id.
+   */
+  private BlockPoolSliceScanner getNextBPScanner(String currentBpId) {
+    
+    String nextBpId = null;
+    while ((nextBpId == null) && datanode.shouldRun
+        && !blockScannerThread.isInterrupted()) {
+      waitForInit(currentBpId);
+      synchronized (this) {
+        if (getBlockPoolSetSize() > 0) {          
+          // Find nextBpId by finding the last modified current log file, if any
+          long lastScanTime = -1;
+          Iterator<String> bpidIterator = blockPoolScannerMap.keySet()
+              .iterator();
+          while (bpidIterator.hasNext()) {
+            String bpid = bpidIterator.next();
+            for (FSDataset.FSVolume vol : dataset.volumes.getVolumes()) {
+              try {
+                File currFile = BlockPoolSliceScanner.getCurrentFile(vol, bpid);
+                if (currFile.exists()) {
+                  long lastModified = currFile.lastModified();
+                  if (lastScanTime < lastModified) {
+                    lastScanTime = lastModified;
+                    nextBpId = bpid;
+                  }
+                }
+              } catch (IOException e) {
+                LOG.warn("Received exception: ", e);
+              }
+            }
+          }
+          
+          // nextBpId can still be null if no current log is found,
+          // find nextBpId sequentially.
+          if (nextBpId == null) {
+            if ("".equals(currentBpId)) {
+              nextBpId = blockPoolScannerMap.firstKey();
+            } else {
+              nextBpId = blockPoolScannerMap.higherKey(currentBpId);
+              if (nextBpId == null) {
+                nextBpId = blockPoolScannerMap.firstKey();
+              }
+            }
+          }
+          if (nextBpId != null) {
+            return getBPScanner(nextBpId);
+          }
+        }
+      }
+      LOG.warn("No block pool is up, going to wait");
+      try {
+        Thread.sleep(5000);
+      } catch (InterruptedException ex) {
+        LOG.warn("Received exception: " + ex);
+        blockScannerThread.interrupt();
+        return null;
+      }
     }
+    return null;
   }
 
-  /** @return the last scan time */
-  synchronized long getLastScanTime(Block block) {
-    if (!isInitialized()) {
-      return 0;
-    }
-    BlockScanInfo info = blockMap.get(block);
-    return info == null? 0: info.lastScanTime;
+  private synchronized int getBlockPoolSetSize() {
+    return blockPoolScannerMap.size();
   }
-
-  /** Deletes blocks from internal structures */
-  void deleteBlocks(Block[] blocks) {
-    for ( Block b : blocks ) {
-      deleteBlock(b);
-    }
+  
+  private synchronized BlockPoolSliceScanner getBPScanner(String bpid) {
+    return blockPoolScannerMap.get(bpid);
   }
   
-  void verifiedByClient(Block block) {
-    updateScanStatus(block, ScanType.REMOTE_READ, true);
+  private synchronized String[] getBpIdList() {
+    return blockPoolScannerMap.keySet().toArray(
+        new String[blockPoolScannerMap.keySet().size()]);
   }
   
-  private synchronized void updateScanStatus(Block block, 
-                                             ScanType type,
-                                             boolean scanOk) {
-    if (!isInitialized()) {
-      return;
-    }
-    BlockScanInfo info = blockMap.get(block);
-    
-    if ( info != null ) {
-      delBlockInfo(info);
+  public void addBlock(ExtendedBlock block) {
+    BlockPoolSliceScanner bpScanner = getBPScanner(block.getBlockPoolId());
+    if (bpScanner != null) {
+      bpScanner.addBlock(block);
     } else {
-      // It might already be removed. Thats ok, it will be caught next time.
-      info = new BlockScanInfo(block);
-    }
-    
-    long now = System.currentTimeMillis();
-    info.lastScanType = type;
-    info.lastScanTime = now;
-    info.lastScanOk = scanOk;
-    addBlockInfo(info);
-    
-    if (type == ScanType.REMOTE_READ) {
-      totalVerifications++;
-    }
-        
-    // Don't update meta data too often in case of REMOTE_READ
-    // of if the verification failed.
-    long diff = now - info.lastLogTime;
-    if (!scanOk || (type == ScanType.REMOTE_READ &&
-                    diff < scanPeriod/3 && diff < ONE_DAY)) {
-      return;
-    }
-    
-    info.lastLogTime = now;
-    LogFileHandler log = verificationLog;
-    if (log != null) {
-      log.appendLine("date=\"" + dateFormat.format(new Date(now)) + "\"\t " +
-          "time=\"" + now + "\"\t " +
-          "genstamp=\"" + block.getGenerationStamp() + "\"\t " +
-          "id=\"" + block.getBlockId() +"\"");
+      LOG.warn("No block pool scanner found for block pool id: "
+          + block.getBlockPoolId());
     }
   }
   
-  private void handleScanFailure(Block block) {
-    
-    LOG.info("Reporting bad block " + block + " to namenode.");
-    
-    try {
-      DatanodeInfo[] dnArr = { new DatanodeInfo(datanode.dnRegistration) };
-      LocatedBlock[] blocks = { new LocatedBlock(block, dnArr) }; 
-      datanode.namenode.reportBadBlocks(blocks);
-    } catch (IOException e){
-      /* One common reason is that NameNode could be in safe mode.
-       * Should we keep on retrying in that case?
-       */
-      LOG.warn("Failed to report bad block " + block + " to namenode : " +
-               " Exception : " + StringUtils.stringifyException(e));
+  public synchronized boolean isInitialized(String bpid) {
+    BlockPoolSliceScanner bpScanner = getBPScanner(bpid);
+    if (bpScanner != null) {
+      return bpScanner.isInitialized();
     }
+    return false;
   }
-  
-  static private class LogEntry {
-    long blockId = -1;
-    long verificationTime = -1;
-    long genStamp = GenerationStamp.GRANDFATHER_GENERATION_STAMP;
-    
-    /**
-     * The format consists of single line with multiple entries. each 
-     * entry is in the form : name="value".
-     * This simple text and easily extendable and easily parseable with a
-     * regex.
-     */
-    private static Pattern entryPattern = 
-      Pattern.compile("\\G\\s*([^=\\p{Space}]+)=\"(.*?)\"\\s*");
-    
-    static LogEntry parseEntry(String line) {
-      LogEntry entry = new LogEntry();
-      
-      Matcher matcher = entryPattern.matcher(line);
-      while (matcher.find()) {
-        String name = matcher.group(1);
-        String value = matcher.group(2);
-        
-        try {
-          if (name.equals("id")) {
-            entry.blockId = Long.valueOf(value);
-          } else if (name.equals("time")) {
-            entry.verificationTime = Long.valueOf(value);
-          } else if (name.equals("genstamp")) {
-            entry.genStamp = Long.valueOf(value);
-          }
-        } catch(NumberFormatException nfe) {
-          LOG.warn("Cannot parse line: " + line, nfe);
-          return null;
-        }
-      }
-      
-      return entry;
+
+  public synchronized void printBlockReport(StringBuilder buffer,
+      boolean summary) {
+    String[] bpIdList = getBpIdList();
+    if (bpIdList == null || bpIdList.length == 0) {
+      buffer.append("Periodic block scanner is not yet initialized. "
+          + "Please check back again after some time.");
+      return;
+    }
+    for (String bpid : bpIdList) {
+      BlockPoolSliceScanner bpScanner = getBPScanner(bpid);
+      buffer.append("\n\nBlock report for block pool: "+bpid + "\n");
+      bpScanner.printBlockReport(buffer, summary);
+      buffer.append("\n");
     }
   }
   
-  private synchronized void adjustThrottler() {
-    long timeLeft = currentPeriodStart+scanPeriod - System.currentTimeMillis();
-    long bw = Math.max(bytesLeft*1000/timeLeft, MIN_SCAN_RATE);
-    throttler.setBandwidth(Math.min(bw, MAX_SCAN_RATE));
+  public void deleteBlock(String poolId, Block toDelete) {
+    BlockPoolSliceScanner bpScanner = getBPScanner(poolId);
+    if (bpScanner != null) {
+      bpScanner.deleteBlock(toDelete);
+    } else {
+      LOG.warn("No block pool scanner found for block pool id: "
+          + poolId);
+    }
   }
-  
-  private void verifyBlock(Block block) {
-    
-    BlockSender blockSender = null;
-
-    /* In case of failure, attempt to read second time to reduce
-     * transient errors. How do we flush block data from kernel 
-     * buffers before the second read? 
-     */
-    for (int i=0; i<2; i++) {
-      boolean second = (i > 0);
-      
-      try {
-        adjustThrottler();
-        
-        blockSender = new BlockSender(block, 0, -1, false, 
-                                               false, true, datanode);
-
-        DataOutputStream out = 
-                new DataOutputStream(new IOUtils.NullOutputStream());
-        
-        blockSender.sendBlock(out, null, throttler);
-
-        LOG.info((second ? "Second " : "") +
-                 "Verification succeeded for " + block);
-        
-        if ( second ) {
-          totalTransientErrors++;
-        }
-        
-        updateScanStatus(block, ScanType.VERIFICATION_SCAN, true);
 
-        return;
-      } catch (IOException e) {
-
-        updateScanStatus(block, ScanType.VERIFICATION_SCAN, false);
-
-        // If the block does not exists anymore, then its not an error
-        if ( dataset.getFile(block) == null ) {
-          LOG.info("Verification failed for " + block + ". Its ok since " +
-          "it not in datanode dataset anymore.");
-          deleteBlock(block);
-          return;
-        }
-
-        LOG.warn((second ? "Second " : "First ") + 
-                 "Verification failed for " + block + ". Exception : " +
-                 StringUtils.stringifyException(e));
-        
-        if (second) {
-          totalScanErrors++;
-          datanode.getMetrics().blockVerificationFailures.inc(); 
-          handleScanFailure(block);
-          return;
-        } 
-      } finally {
-        IOUtils.closeStream(blockSender);
-        datanode.getMetrics().blocksVerified.inc();
-        totalScans++;
-        totalVerifications++;
-      }
+  public void deleteBlocks(String poolId, Block[] toDelete) {
+    BlockPoolSliceScanner bpScanner = getBPScanner(poolId);
+    if (bpScanner != null) {
+      bpScanner.deleteBlocks(toDelete);
+    } else {
+      LOG.warn("No block pool scanner found for block pool id: "
+          + poolId);
     }
   }
   
-  private synchronized long getEarliestScanTime() {
-    if ( blockInfoSet.size() > 0 ) {
-      return blockInfoSet.first().lastScanTime;
-    }
-    return Long.MAX_VALUE; 
-  }
-  
-  // Picks one block and verifies it
-  private void verifyFirstBlock() {
-    Block block = null;
-    synchronized (this) {
-      if ( blockInfoSet.size() > 0 ) {
-        block = blockInfoSet.first().block;
-      }
-    }
-    
-    if ( block != null ) {
-      verifyBlock(block);
+  public synchronized void shutdown() {
+    if (blockScannerThread != null) {
+      blockScannerThread.interrupt();
     }
   }
-  
-  /** returns false if the process was interrupted
-   * because the thread is marked to exit.
-   */
-  private boolean assignInitialVerificationTimes() {
-    int numBlocks = 1;
-    LogFileHandler log = null;
-    synchronized (this) {
-      log = verificationLog;
-      numBlocks = Math.max(blockMap.size(), 1);
-    }
-    
-    //First udpates the last verification times from the log file.
-    LogFileHandler.Reader logReader = null;
-    try {
-      if (log != null) {
-        logReader = log.new Reader(false);
-      }
-    } catch (IOException e) {
-      LOG.warn("Could not read previous verification times : " +
-               StringUtils.stringifyException(e));
-    }
-    
-    if (log != null) {
-      log.updateCurNumLines();
-    }
-    
-    try {
-    // update verification times from the verificationLog.
-    while (logReader != null && logReader.hasNext()) {
-      if (!datanode.shouldRun || Thread.interrupted()) {
-        return false;
-      }
-      LogEntry entry = LogEntry.parseEntry(logReader.next());
-      if (entry != null) {
-        updateBlockInfo(entry);
-      }
-    }
-    } finally {
-      IOUtils.closeStream(logReader);
-    }
-    
-    /* Initially spread the block reads over half of 
-     * MIN_SCAN_PERIOD so that we don't keep scanning the 
-     * blocks too quickly when restarted.
-     */
-    long verifyInterval = (long) (Math.min( scanPeriod/2.0/numBlocks,
-                                            10*60*1000 ));
-    long lastScanTime = System.currentTimeMillis() - scanPeriod;
-    
-    /* Before this loop, entries in blockInfoSet that are not
-     * updated above have lastScanTime of <= 0 . Loop until first entry has
-     * lastModificationTime > 0.
-     */    
-    synchronized (this) {
-      if (blockInfoSet.size() > 0 ) {
-        BlockScanInfo info;
-        while ((info =  blockInfoSet.first()).lastScanTime < 0) {
-          delBlockInfo(info);        
-          info.lastScanTime = lastScanTime;
-          lastScanTime += verifyInterval;
-          addBlockInfo(info);
-        }
-      }
+
+  public synchronized void addBlockPool(String blockPoolId) {
+    if (blockPoolScannerMap.get(blockPoolId) != null) {
+      return;
     }
-    
-    return true;
-  }
-  
-  private synchronized void startNewPeriod() {
-    LOG.info("Starting a new period : work left in prev period : " +
-             String.format("%.2f%%", (bytesLeft * 100.0)/totalBytesToScan));
-    // reset the byte counts :
-    bytesLeft = totalBytesToScan;
-    currentPeriodStart = System.currentTimeMillis();
-  }
-  
-  public void run() {
+    BlockPoolSliceScanner bpScanner = new BlockPoolSliceScanner(datanode, dataset,
+        conf, blockPoolId);
     try {
-      
-      init();
-      
-      //Read last verification times
-      if (!assignInitialVerificationTimes()) {
-        return;
-      }
-      
-      adjustThrottler();
-      
-      while (datanode.shouldRun && !Thread.interrupted()) {
-        long now = System.currentTimeMillis();
-        synchronized (this) {
-          if ( now >= (currentPeriodStart + scanPeriod)) {
-            startNewPeriod();
-          }
-        }
-        if (dirScanner.newScanPeriod(now)) {
-          dirScanner.reconcile();
-          now = System.currentTimeMillis();
-        }
-        if ( (now - getEarliestScanTime()) >= scanPeriod ) {
-          verifyFirstBlock();
-        } else {
-          try {
-            Thread.sleep(1000);
-          } catch (InterruptedException ignored) {}
-        }
-      }
-    } catch (RuntimeException e) {
-      LOG.warn("RuntimeException during DataBlockScanner.run() : " +
-               StringUtils.stringifyException(e));
-      throw e;
-    } finally {
-      shutdown();
-      LOG.info("Exiting DataBlockScanner thread.");
+      bpScanner.init();
+    } catch (IOException ex) {
+      LOG.warn("Failed to initialized block scanner for pool id="+blockPoolId);
+      return;
     }
+    blockPoolScannerMap.put(blockPoolId, bpScanner);
+    LOG.info("Added bpid=" + blockPoolId + " to blockPoolScannerMap, new size="
+        + blockPoolScannerMap.size());
   }
   
-  synchronized void shutdown() {
-    LogFileHandler log = verificationLog;
-    verificationLog = null;
-    dirScanner.shutdown();
-    if (log != null) {
-      log.close();
-    }
+  public synchronized void removeBlockPool(String blockPoolId) {
+    blockPoolScannerMap.remove(blockPoolId);
+    LOG.info("Removed bpid="+blockPoolId+" from blockPoolScannerMap");
   }
   
-  synchronized void printBlockReport(StringBuilder buffer, 
-                                     boolean summaryOnly) {
-    long oneHour = 3600*1000;
-    long oneDay = 24*oneHour;
-    long oneWeek = 7*oneDay;
-    long fourWeeks = 4*oneWeek;
-    
-    int inOneHour = 0;
-    int inOneDay = 0;
-    int inOneWeek = 0;
-    int inFourWeeks = 0;
-    int inScanPeriod = 0;
-    int neverScanned = 0;
-    
-    int total = blockInfoSet.size();
-    
-    long now = System.currentTimeMillis();
-    
-    Date date = new Date();
-    
-    for(Iterator<BlockScanInfo> it = blockInfoSet.iterator(); it.hasNext();) {
-      BlockScanInfo info = it.next();
-      
-      long scanTime = info.getLastScanTime();
-      long diff = now - scanTime;
-      
-      if (diff <= oneHour) inOneHour++;
-      if (diff <= oneDay) inOneDay++;
-      if (diff <= oneWeek) inOneWeek++;
-      if (diff <= fourWeeks) inFourWeeks++;
-      if (diff <= scanPeriod) inScanPeriod++;      
-      if (scanTime <= 0) neverScanned++;
-      
-      if (!summaryOnly) {
-        date.setTime(scanTime);
-        String scanType = 
-          (info.lastScanType == ScanType.REMOTE_READ) ? "remote" : 
-            ((info.lastScanType == ScanType.VERIFICATION_SCAN) ? "local" :
-              "none");
-        buffer.append(String.format("%-26s : status : %-6s type : %-6s" +
-                                    " scan time : " +
-                                    "%-15d %s\n", info.block, 
-                                    (info.lastScanOk ? "ok" : "failed"),
-                                    scanType, scanTime,
-                                    (scanTime <= 0) ? "not yet verified" : 
-                                      dateFormat.format(date)));
-      }
+  // This method is used for testing
+  long getBlocksScannedInLastRun(String bpid) throws IOException {
+    BlockPoolSliceScanner bpScanner = getBPScanner(bpid);
+    if (bpScanner == null) {
+      throw new IOException("Block Pool: "+bpid+" is not running");
+    } else {
+      return bpScanner.getBlocksScannedInLastRun();
     }
-    
-    double pctPeriodLeft = (scanPeriod + currentPeriodStart - now)
-                           *100.0/scanPeriod;
-    double pctProgress = (totalBytesToScan == 0) ? 100 :
-                         (totalBytesToScan-bytesLeft)*10000.0/totalBytesToScan/
-                         (100-pctPeriodLeft+1e-10);
-    
-    buffer.append(String.format("\nTotal Blocks                 : %6d" +
-                                "\nVerified in last hour        : %6d" +
-                                "\nVerified in last day         : %6d" +
-                                "\nVerified in last week        : %6d" +
-                                "\nVerified in last four weeks  : %6d" +
-                                "\nVerified in SCAN_PERIOD      : %6d" +
-                                "\nNot yet verified             : %6d" +
-                                "\nVerified since restart       : %6d" +
-                                "\nScans since restart          : %6d" +
-                                "\nScan errors since restart    : %6d" +
-                                "\nTransient scan errors        : %6d" +
-                                "\nCurrent scan rate limit KBps : %6d" +
-                                "\nProgress this period         : %6.0f%%" +
-                                "\nTime left in cur period      : %6.2f%%" +
-                                "\n", 
-                                total, inOneHour, inOneDay, inOneWeek,
-                                inFourWeeks, inScanPeriod, neverScanned,
-                                totalVerifications, totalScans, 
-                                totalScanErrors, totalTransientErrors, 
-                                Math.round(throttler.getBandwidth()/1024.0),
-                                pctProgress, pctPeriodLeft));
   }
-  
-  /**
-   * This class takes care of log file used to store the last verification
-   * times of the blocks. It rolls the current file when it is too big etc.
-   * If there is an error while writing, it stops updating with an error
-   * message.
-   */
-  private static class LogFileHandler {
-    
-    private static final String curFileSuffix = ".curr";
-    private static final String prevFileSuffix = ".prev";
-    
-    // Don't roll files more often than this
-    private static final long minRollingPeriod = 6 * 3600 * 1000L; // 6 hours
-    private static final long minWarnPeriod = minRollingPeriod;
-    private static final int minLineLimit = 1000;
-    
-    
-    static boolean isFilePresent(File dir, String filePrefix) {
-      return new File(dir, filePrefix + curFileSuffix).exists() ||
-             new File(dir, filePrefix + prevFileSuffix).exists();
-    }
-    private File curFile;
-    private File prevFile;
-    
-    private int maxNumLines = -1; // not very hard limit on number of lines.
-    private int curNumLines = -1;
-    
-    long lastWarningTime = 0;
-    
-    private PrintStream out;
-    
-    int numReaders = 0;
-        
-    /**
-     * Opens the log file for appending.
-     * Note that rolling will happen only after "updateLineCount()" is 
-     * called. This is so that line count could be updated in a separate
-     * thread without delaying start up.
-     * 
-     * @param dir where the logs files are located.
-     * @param filePrefix prefix of the file.
-     * @param maxNumLines max lines in a file (its a soft limit).
-     * @throws IOException
-     */
-    LogFileHandler(File dir, String filePrefix, int maxNumLines) 
-                                                throws IOException {
-      curFile = new File(dir, filePrefix + curFileSuffix);
-      prevFile = new File(dir, filePrefix + prevFileSuffix);
-      openCurFile();
-      curNumLines = -1;
-      setMaxNumLines(maxNumLines);
-    }
-    
-    // setting takes affect when next entry is added.
-    synchronized void setMaxNumLines(int maxNumLines) {
-      this.maxNumLines = Math.max(maxNumLines, minLineLimit);
-    }
-    
-    /**
-     * Append "\n" + line.
-     * If the log file need to be rolled, it will done after 
-     * appending the text.
-     * This does not throw IOException when there is an error while 
-     * appending. Currently does not throw an error even if rolling 
-     * fails (may be it should?).
-     * return true if append was successful.
-     */
-    synchronized boolean appendLine(String line) {
-      out.println();
-      out.print(line);
-      curNumLines += (curNumLines < 0) ? -1 : 1;
-      try {
-        rollIfRequired();
-      } catch (IOException e) {
-        warn("Rolling failed for " + curFile + " : " + e.getMessage());
-        return false;
-      }
-      return true;
-    }
-    
-    //warns only once in a while
-    synchronized private void warn(String msg) {
-      long now = System.currentTimeMillis();
-      if ((now - lastWarningTime) >= minWarnPeriod) {
-        lastWarningTime = now;
-        LOG.warn(msg);
-      }
-    }
-    
-    private synchronized void openCurFile() throws FileNotFoundException {
-      close();
-      out = new PrintStream(new FileOutputStream(curFile, true));
-    }
-    
-    //This reads the current file and updates the count.
-    void updateCurNumLines() {
-      int count = 0;
-      Reader it = null;
-      try {
-        for(it = new Reader(true); it.hasNext(); count++) {
-          it.next();
-        }
-      } catch (IOException e) {
-        
-      } finally {
-        synchronized (this) {
-          curNumLines = count;
-        }
-        IOUtils.closeStream(it);
-      }
-    }
-    
-    private void rollIfRequired() throws IOException {
-      if (curNumLines < maxNumLines || numReaders > 0) {
-        return;
-      }
-      
-      long now = System.currentTimeMillis();
-      if (now < minRollingPeriod) {
-        return;
-      }
-      
-      if (!prevFile.delete() && prevFile.exists()) {
-        throw new IOException("Could not delete " + prevFile);
-      }
-      
-      close();
-
-      if (!curFile.renameTo(prevFile)) {
-        openCurFile();
-        throw new IOException("Could not rename " + curFile + 
-                              " to " + prevFile);
-      }
-      
-      openCurFile();
-      updateCurNumLines();
-    }
-    
-    synchronized void close() {
-      if (out != null) {
-        out.close();
-        out = null;
-      }
-    }
-    
-    /**
-     * This is used to read the lines in order.
-     * If the data is not read completely (i.e, untill hasNext() returns
-     * false), it needs to be explicitly 
-     */
-    private class Reader implements Iterator<String>, Closeable {
-      
-      BufferedReader reader;
-      File file;
-      String line;
-      boolean closed = false;
-      
-      private Reader(boolean skipPrevFile) throws IOException {
-        synchronized (LogFileHandler.this) {
-          numReaders++; 
-        }
-        reader = null;
-        file = (skipPrevFile) ? curFile : prevFile;
-        readNext();        
-      }
-      
-      private boolean openFile() throws IOException {
-
-        for(int i=0; i<2; i++) {
-          if (reader != null || i > 0) {
-            // move to next file
-            file = (file == prevFile) ? curFile : null;
-          }
-          if (file == null) {
-            return false;
-          }
-          if (file.exists()) {
-            break;
-          }
-        }
-        
-        if (reader != null ) {
-          reader.close();
-          reader = null;
-        }
-        
-        reader = new BufferedReader(new FileReader(file));
-        return true;
-      }
-      
-      // read next line if possible.
-      private void readNext() throws IOException {
-        line = null;
-        try {
-          if (reader != null && (line = reader.readLine()) != null) {
-            return;
-          }
-          if (line == null) {
-            // move to the next file.
-            if (openFile()) {
-              readNext();
-            }
-          }
-        } finally {
-          if (!hasNext()) {
-            close();
-          }
-        }
-      }
-      
-      public boolean hasNext() {
-        return line != null;
-      }
 
-      public String next() {
-        String curLine = line;
-        try {
-          readNext();
-        } catch (IOException e) {
-          LOG.info("Could not reade next line in LogHandler : " +
-                   StringUtils.stringifyException(e));
-        }
-        return curLine;
-      }
-
-      public void remove() {
-        throw new RuntimeException("remove() is not supported.");
-      }
-
-      public void close() throws IOException {
-        if (!closed) {
-          try {
-            if (reader != null) {
-              reader.close();
-            }
-          } finally {
-            file = null;
-            reader = null;
-            closed = true;
-            synchronized (LogFileHandler.this) {
-              numReaders--;
-              assert(numReaders >= 0);
-            }
-          }
-        }
-      }
-    }    
+  public void start() {
+    blockScannerThread = new Thread(this);
+    blockScannerThread.setDaemon(true);
+    blockScannerThread.start();
   }
   
   @InterfaceAudience.Private
@@ -967,25 +299,23 @@ class DataBlockScanner implements Runnab
 
     public void doGet(HttpServletRequest request, 
                       HttpServletResponse response) throws IOException {
-      
       response.setContentType("text/plain");
       
-      DataBlockScanner blockScanner = (DataBlockScanner)  
-          getServletContext().getAttribute("datanode.blockScanner");
+      DataNode datanode = (DataNode) getServletContext().getAttribute("datanode");
+      DataBlockScanner blockScanner = datanode.blockScanner;
       
       boolean summary = (request.getParameter("listblocks") == null);
       
       StringBuilder buffer = new StringBuilder(8*1024);
       if (blockScanner == null) {
+        LOG.warn("Periodic block scanner is not running");
         buffer.append("Periodic block scanner is not running. " +
                       "Please check the datanode log if this is unexpected.");
-      } else if (blockScanner.isInitialized()) {
-        blockScanner.printBlockReport(buffer, summary);
       } else {
-        buffer.append("Periodic block scanner is not yet initialized. " +
-                      "Please check back again after some time.");
+        blockScanner.printBlockReport(buffer, summary);
       }
       response.getWriter().write(buffer.toString()); // extra copy!
     }
   }
+
 }



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