HBASE-7213 Have HLog files for .META. edits only

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1431935 13f79535-47bb-0310-9956-ffa450edef68

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -960,6 +960,7 @@ Server {
       return;
     }
     LOG.info("Forcing splitLog and expire of " + sn);
+    fileSystemManager.splitMetaLog(sn);
     fileSystemManager.splitLog(sn);
     serverManager.expireServer(sn);
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterFileSystem.java

@@ -32,6 +32,7 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.PathFilter;
 import org.apache.hadoop.hbase.ClusterId;
 import org.apache.hadoop.hbase.DeserializationException;
 import org.apache.hadoop.hbase.HColumnDescriptor;
@@ -84,6 +85,18 @@ public class MasterFileSystem {
   final SplitLogManager splitLogManager;
   private final MasterServices services;
 
+  private final static PathFilter META_FILTER = new PathFilter() {
+    public boolean accept(Path p) {
+      return HLogUtil.isMetaFile(p);
+    }
+  };
+
+  private final static PathFilter NON_META_FILTER = new PathFilter() {
+    public boolean accept(Path p) {
+      return !HLogUtil.isMetaFile(p);
+    }
+  };
+
   public MasterFileSystem(Server master, MasterServices services,
       MetricsMaster metricsMaster, boolean masterRecovery)
   throws IOException {
@@ -229,7 +242,8 @@ public class MasterFileSystem {
                 + " belongs to an existing region server");
           }
         }
-        splitLog(serverNames);
+        splitLog(serverNames, META_FILTER);
+        splitLog(serverNames, NON_META_FILTER);
         retrySplitting = false;
       } catch (IOException ioe) {
         LOG.warn("Failed splitting of " + serverNames, ioe);
@@ -258,8 +272,30 @@ public class MasterFileSystem {
     splitLog(serverNames);
   }
 
-  public void splitLog(final List<ServerName> serverNames) throws IOException {
+  /**
+   * Specialized method to handle the splitting for .META. HLog
+   * @param serverName
+   * @throws IOException
+   */
+  public void splitMetaLog(final ServerName serverName) throws IOException {
     long splitTime = 0, splitLogSize = 0;
+    List<ServerName> serverNames = new ArrayList<ServerName>();
+    serverNames.add(serverName);
+    List<Path> logDirs = getLogDirs(serverNames);
+    if (logDirs.isEmpty()) {
+      LOG.info("No .META. logs to split");
+      return;
+    }
+    splitLogManager.handleDeadWorkers(serverNames);
+    splitTime = EnvironmentEdgeManager.currentTimeMillis();
+    splitLogSize = splitLogManager.splitLogDistributed(logDirs, META_FILTER);
+    splitTime = EnvironmentEdgeManager.currentTimeMillis() - splitTime;
+    if (this.metricsMaster != null) {
+      this.metricsMaster.addSplit(splitTime, splitLogSize);
+    }
+  }
+
+  private List<Path> getLogDirs(final List<ServerName> serverNames) throws IOException {
     List<Path> logDirs = new ArrayList<Path>();
     for (ServerName serverName: serverNames) {
       Path logDir = new Path(this.rootdir, HLogUtil.getHLogDirectoryName(serverName.toString()));
@@ -277,6 +313,23 @@ public class MasterFileSystem {
       }
       logDirs.add(splitDir);
     }
+    return logDirs;
+  }
+
+  public void splitLog(final List<ServerName> serverNames) throws IOException {
+    splitLog(serverNames, NON_META_FILTER);
+  }
+
+  /**
+   * This method is the base split method that splits HLog files matching a filter.
+   * Callers should pass the appropriate filter for .META. and non-meta HLogs.
+   * @param serverNames
+   * @param filter
+   * @throws IOException
+   */
+  public void splitLog(final List<ServerName> serverNames, PathFilter filter) throws IOException {
+    long splitTime = 0, splitLogSize = 0;
+    List<Path> logDirs = getLogDirs(serverNames);
 
     if (logDirs.isEmpty()) {
       LOG.info("No logs to split");
@@ -286,7 +339,7 @@ public class MasterFileSystem {
     if (distributedLogSplitting) {
       splitLogManager.handleDeadWorkers(serverNames);
       splitTime = EnvironmentEdgeManager.currentTimeMillis();
-      splitLogSize = splitLogManager.splitLogDistributed(logDirs);
+      splitLogSize = splitLogManager.splitLogDistributed(logDirs,filter);
       splitTime = EnvironmentEdgeManager.currentTimeMillis() - splitTime;
     } else {
       for(Path logDir: logDirs){
@@ -370,7 +423,8 @@ public class MasterFileSystem {
     // Make sure cluster ID exists
     if (!FSUtils.checkClusterIdExists(fs, rd, c.getInt(
         HConstants.THREAD_WAKE_FREQUENCY, 10 * 1000))) {
-      FSUtils.setClusterId(fs, rd, new ClusterId(), c.getInt(HConstants.THREAD_WAKE_FREQUENCY, 10 * 1000));
+      FSUtils.setClusterId(fs, rd, new ClusterId(), c.getInt(HConstants.THREAD_WAKE_FREQUENCY,
+        10 * 1000));
     }
     clusterId = FSUtils.getClusterId(fs, rd);
 

hbase-server/src/main/java/org/apache/hadoop/hbase/master/SplitLogManager.java

@@ -40,6 +40,7 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.PathFilter;
 import org.apache.hadoop.hbase.Chore;
 import org.apache.hadoop.hbase.SplitLogCounters;
 import org.apache.hadoop.hbase.DeserializationException;
@@ -51,6 +52,7 @@ import org.apache.hadoop.hbase.monitoring.MonitoredTask;
 import org.apache.hadoop.hbase.monitoring.TaskMonitor;
 import org.apache.hadoop.hbase.regionserver.SplitLogWorker;
 import org.apache.hadoop.hbase.regionserver.wal.HLogSplitter;
+import org.apache.hadoop.hbase.regionserver.wal.HLogUtil;
 import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
 import org.apache.hadoop.hbase.util.FSUtils;
 import org.apache.hadoop.hbase.util.Threads;
@@ -194,7 +196,7 @@ public class SplitLogManager extends ZooKeeperListener {
     }
   }
 
-  private FileStatus[] getFileList(List<Path> logDirs) throws IOException {
+  private FileStatus[] getFileList(List<Path> logDirs, PathFilter filter) throws IOException {
     List<FileStatus> fileStatus = new ArrayList<FileStatus>();
     for (Path hLogDir : logDirs) {
       this.fs = hLogDir.getFileSystem(conf);
@@ -202,8 +204,7 @@ public class SplitLogManager extends ZooKeeperListener {
         LOG.warn(hLogDir + " doesn't exist. Nothing to do!");
         continue;
       }
-      // TODO filter filenames?
+      FileStatus[] logfiles = FSUtils.listStatus(fs, hLogDir, filter);
-      FileStatus[] logfiles = FSUtils.listStatus(fs, hLogDir, null);
       if (logfiles == null || logfiles.length == 0) {
         LOG.info(hLogDir + " is empty dir, no logs to split");
       } else {
@@ -228,6 +229,7 @@ public class SplitLogManager extends ZooKeeperListener {
     logDirs.add(logDir);
     return splitLogDistributed(logDirs);
   }
+
   /**
    * The caller will block until all the log files of the given region server
    * have been processed - successfully split or an error is encountered - by an
@@ -239,9 +241,25 @@ public class SplitLogManager extends ZooKeeperListener {
    * @return cumulative size of the logfiles split
    */
   public long splitLogDistributed(final List<Path> logDirs) throws IOException {
+    return splitLogDistributed(logDirs, null);
+  }
+
+  /**
+   * The caller will block until all the META log files of the given region server
+   * have been processed - successfully split or an error is encountered - by an
+   * available worker region server. This method must only be called after the
+   * region servers have been brought online.
+   *
+   * @param logDirs List of log dirs to split
+   * @param filter the Path filter to select specific files for considering
+   * @throws IOException If there was an error while splitting any log file
+   * @return cumulative size of the logfiles split
+   */
+  public long splitLogDistributed(final List<Path> logDirs, PathFilter filter) 
+      throws IOException {
     MonitoredTask status = TaskMonitor.get().createStatus(
           "Doing distributed log split in " + logDirs);
-    FileStatus[] logfiles = getFileList(logDirs);
+    FileStatus[] logfiles = getFileList(logDirs, filter);
     status.setStatus("Checking directory contents...");
     LOG.debug("Scheduling batch of logs to split");
     SplitLogCounters.tot_mgr_log_split_batch_start.incrementAndGet();

hbase-server/src/main/java/org/apache/hadoop/hbase/master/handler/MetaServerShutdownHandler.java

@@ -18,11 +18,17 @@
  */
 package org.apache.hadoop.hbase.master.handler;
 
+import java.io.IOException;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hbase.HRegionInfo;
 import org.apache.hadoop.hbase.Server;
 import org.apache.hadoop.hbase.ServerName;
 import org.apache.hadoop.hbase.master.DeadServer;
 import org.apache.hadoop.hbase.master.MasterServices;
+import org.apache.zookeeper.KeeperException;
 
 /**
  * Shutdown handler for the server hosting <code>-ROOT-</code>,
@@ -32,7 +38,7 @@ import org.apache.hadoop.hbase.master.MasterServices;
 public class MetaServerShutdownHandler extends ServerShutdownHandler {
   private final boolean carryingRoot;
   private final boolean carryingMeta;
-
+  private static final Log LOG = LogFactory.getLog(MetaServerShutdownHandler.class);
   public MetaServerShutdownHandler(final Server server,
       final MasterServices services,
       final DeadServer deadServers, final ServerName serverName,
@@ -44,11 +50,118 @@ public class MetaServerShutdownHandler extends ServerShutdownHandler {
   }
 
   @Override
+  public void process() throws IOException {
+    try {
+      LOG.info("Splitting META logs for " + serverName);
+      if (this.shouldSplitHlog) {
+        this.services.getMasterFileSystem().splitMetaLog(serverName);
+      }
+    } catch (IOException ioe) {
+      this.services.getExecutorService().submit(this);
+      this.deadServers.add(serverName);
+      throw new IOException("failed log splitting for " +
+          serverName + ", will retry", ioe);
+    }
+
+    // Assign root and meta if we were carrying them.
+    if (isCarryingRoot()) { // -ROOT-
+      // Check again: region may be assigned to other where because of RIT
+      // timeout
+      if (this.services.getAssignmentManager().isCarryingRoot(serverName)) {
+        LOG.info("Server " + serverName
+            + " was carrying ROOT. Trying to assign.");
+        this.services.getAssignmentManager().regionOffline(
+            HRegionInfo.ROOT_REGIONINFO);
+        verifyAndAssignRootWithRetries();
+      } else {
+        LOG.info("ROOT has been assigned to otherwhere, skip assigning.");
+      }
+    }
+
+    // Carrying meta?
+    if (isCarryingMeta()) {
+      // Check again: region may be assigned to other where because of RIT
+      // timeout
+      if (this.services.getAssignmentManager().isCarryingMeta(serverName)) {
+        LOG.info("Server " + serverName
+            + " was carrying META. Trying to assign.");
+        this.services.getAssignmentManager().regionOffline(
+            HRegionInfo.FIRST_META_REGIONINFO);
+        this.services.getAssignmentManager().assignMeta();
+      } else {
+        LOG.info("META has been assigned to otherwhere, skip assigning.");
+      }
+
+    }
+    super.process();
+  }
+  /**
+   * Before assign the ROOT region, ensure it haven't
+   *  been assigned by other place
+   * <p>
+   * Under some scenarios, the ROOT region can be opened twice, so it seemed online
+   * in two regionserver at the same time.
+   * If the ROOT region has been assigned, so the operation can be canceled.
+   * @throws InterruptedException
+   * @throws IOException
+   * @throws KeeperException
+   */
+  private void verifyAndAssignRoot()
+  throws InterruptedException, IOException, KeeperException {
+    long timeout = this.server.getConfiguration().
+      getLong("hbase.catalog.verification.timeout", 1000);
+    if (!this.server.getCatalogTracker().verifyRootRegionLocation(timeout)) {
+      this.services.getAssignmentManager().assignRoot();
+    } else if (serverName.equals(server.getCatalogTracker().getRootLocation())) {
+      throw new IOException("-ROOT- is onlined on the dead server "
+          + serverName);
+    } else {
+      LOG.info("Skip assigning -ROOT-, because it is online on the "
+          + server.getCatalogTracker().getRootLocation());
+    }
+  }
+
+  /**
+   * Failed many times, shutdown processing
+   * @throws IOException
+   */
+  private void verifyAndAssignRootWithRetries() throws IOException {
+    int iTimes = this.server.getConfiguration().getInt(
+        "hbase.catalog.verification.retries", 10);
+
+    long waitTime = this.server.getConfiguration().getLong(
+        "hbase.catalog.verification.timeout", 1000);
+
+    int iFlag = 0;
+    while (true) {
+      try {
+        verifyAndAssignRoot();
+        break;
+      } catch (KeeperException e) {
+        this.server.abort("In server shutdown processing, assigning root", e);
+        throw new IOException("Aborting", e);
+      } catch (Exception e) {
+        if (iFlag >= iTimes) {
+          this.server.abort("verifyAndAssignRoot failed after" + iTimes
+              + " times retries, aborting", e);
+          throw new IOException("Aborting", e);
+        }
+        try {
+          Thread.sleep(waitTime);
+        } catch (InterruptedException e1) {
+          LOG.warn("Interrupted when is the thread sleep", e1);
+          Thread.currentThread().interrupt();
+          throw new IOException("Interrupted", e1);
+        }
+        iFlag++;
+      }
+    }
+  }
+
   boolean isCarryingRoot() {
     return this.carryingRoot;
   }
 
-  @Override
   boolean isCarryingMeta() {
     return this.carryingMeta;
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/handler/ServerShutdownHandler.java

@@ -55,10 +55,10 @@ import org.apache.zookeeper.KeeperException;
 @InterfaceAudience.Private
 public class ServerShutdownHandler extends EventHandler {
   private static final Log LOG = LogFactory.getLog(ServerShutdownHandler.class);
-  private final ServerName serverName;
+  protected final ServerName serverName;
-  private final MasterServices services;
+  protected final MasterServices services;
-  private final DeadServer deadServers;
+  protected final DeadServer deadServers;
-  private final boolean shouldSplitHlog; // whether to split HLog or not
+  protected final boolean shouldSplitHlog; // whether to split HLog or not
 
   public ServerShutdownHandler(final Server server, final MasterServices services,
       final DeadServer deadServers, final ServerName serverName,
@@ -90,69 +90,6 @@ public class ServerShutdownHandler extends EventHandler {
     }
   }
 
-  /**
-   * Before assign the ROOT region, ensure it haven't
-   *  been assigned by other place
-   * <p>
-   * Under some scenarios, the ROOT region can be opened twice, so it seemed online
-   * in two regionserver at the same time.
-   * If the ROOT region has been assigned, so the operation can be canceled.
-   * @throws InterruptedException
-   * @throws IOException
-   * @throws KeeperException
-   */
-  private void verifyAndAssignRoot()
-  throws InterruptedException, IOException, KeeperException {
-    long timeout = this.server.getConfiguration().
-      getLong("hbase.catalog.verification.timeout", 1000);
-    if (!this.server.getCatalogTracker().verifyRootRegionLocation(timeout)) {
-      this.services.getAssignmentManager().assignRoot();
-    } else if (serverName.equals(server.getCatalogTracker().getRootLocation())) {
-      throw new IOException("-ROOT- is onlined on the dead server "
-          + serverName);
-    } else {
-      LOG.info("Skip assigning -ROOT-, because it is online on the "
-          + server.getCatalogTracker().getRootLocation());
-    }
-  }
-
-  /**
-   * Failed many times, shutdown processing
-   * @throws IOException
-   */
-  private void verifyAndAssignRootWithRetries() throws IOException {
-    int iTimes = this.server.getConfiguration().getInt(
-        "hbase.catalog.verification.retries", 10);
-
-    long waitTime = this.server.getConfiguration().getLong(
-        "hbase.catalog.verification.timeout", 1000);
-
-    int iFlag = 0;
-    while (true) {
-      try {
-        verifyAndAssignRoot();
-        break;
-      } catch (KeeperException e) {
-        this.server.abort("In server shutdown processing, assigning root", e);
-        throw new IOException("Aborting", e);
-      } catch (Exception e) {
-        if (iFlag >= iTimes) {
-          this.server.abort("verifyAndAssignRoot failed after" + iTimes
-              + " times retries, aborting", e);
-          throw new IOException("Aborting", e);
-        }
-        try {
-          Thread.sleep(waitTime);
-        } catch (InterruptedException e1) {
-          LOG.warn("Interrupted when is the thread sleep", e1);
-          Thread.currentThread().interrupt();
-          throw new IOException("Interrupted", e1);
-        }
-        iFlag++;
-      }
-    }
-  }
-
   /**
    * @return True if the server we are processing was carrying <code>-ROOT-</code>
    */
@@ -188,43 +125,13 @@ public class ServerShutdownHandler extends EventHandler {
           LOG.info("Skipping log splitting for " + serverName);
         }
       } catch (IOException ioe) {
-        this.services.getExecutorService().submit(this);
+        //typecast to SSH so that we make sure that it is the SSH instance that
+        //gets submitted as opposed to MSSH or some other derived instance of SSH
+        this.services.getExecutorService().submit((ServerShutdownHandler)this);
         this.deadServers.add(serverName);
         throw new IOException("failed log splitting for " +
           serverName + ", will retry", ioe);
       }
-
-      // Assign root and meta if we were carrying them.
-      if (isCarryingRoot()) { // -ROOT-
-        // Check again: region may be assigned to other where because of RIT
-        // timeout
-        if (this.services.getAssignmentManager().isCarryingRoot(serverName)) {
-          LOG.info("Server " + serverName
-              + " was carrying ROOT. Trying to assign.");
-          this.services.getAssignmentManager().regionOffline(
-              HRegionInfo.ROOT_REGIONINFO);
-          verifyAndAssignRootWithRetries();
-        } else {
-          LOG.info("ROOT has been assigned to otherwhere, skip assigning.");
-        }
-      }
-
-      // Carrying meta?
-      if (isCarryingMeta()) {
-        // Check again: region may be assigned to other where because of RIT
-        // timeout
-        if (this.services.getAssignmentManager().isCarryingMeta(serverName)) {
-          LOG.info("Server " + serverName
-              + " was carrying META. Trying to assign.");
-          this.services.getAssignmentManager().regionOffline(
-              HRegionInfo.FIRST_META_REGIONINFO);
-          this.services.getAssignmentManager().assignMeta();
-        } else {
-          LOG.info("META has been assigned to otherwhere, skip assigning.");
-        }
-       
-      }
-
       // We don't want worker thread in the MetaServerShutdownHandler
       // executor pool to block by waiting availability of -ROOT-
       // and .META. server. Otherwise, it could run into the following issue:

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java

@@ -29,6 +29,7 @@ import java.lang.reflect.Method;
 import java.net.BindException;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
@@ -328,6 +329,7 @@ public class  HRegionServer implements ClientProtocol,
   RpcServer rpcServer;
 
   private final InetSocketAddress isa;
+  private UncaughtExceptionHandler uncaughtExceptionHandler;
 
   // Info server. Default access so can be used by unit tests. REGIONSERVER
   // is name of the webapp and the attribute name used stuffing this instance
@@ -357,7 +359,12 @@ public class  HRegionServer implements ClientProtocol,
   // HLog and HLog roller. log is protected rather than private to avoid
   // eclipse warning when accessed by inner classes
   protected volatile HLog hlog;
+  // The meta updates are written to a different hlog. If this
+  // regionserver holds meta, then this field will be non-null.
+  protected volatile HLog hlogForMeta;
+
   LogRoller hlogRoller;
+  LogRoller metaHLogRoller;
 
   // flag set after we're done setting up server threads (used for testing)
   protected volatile boolean isOnline;
@@ -518,6 +525,11 @@ public class  HRegionServer implements ClientProtocol,
       "hbase.regionserver.kerberos.principal", this.isa.getHostName());
     regionServerAccounting = new RegionServerAccounting();
     cacheConfig = new CacheConfig(conf);
+    uncaughtExceptionHandler = new UncaughtExceptionHandler() {
+      public void uncaughtException(Thread t, Throwable e) {
+        abort("Uncaught exception in service thread " + t.getName(), e);
+      }
+    };
     this.rsHost = new RegionServerCoprocessorHost(this, this.conf);
   }
 
@@ -931,6 +943,7 @@ public class  HRegionServer implements ClientProtocol,
     if (this.cacheFlusher != null) this.cacheFlusher.interruptIfNecessary();
     if (this.compactSplitThread != null) this.compactSplitThread.interruptIfNecessary();
     if (this.hlogRoller != null) this.hlogRoller.interruptIfNecessary();
+    if (this.metaHLogRoller != null) this.metaHLogRoller.interruptIfNecessary();
     if (this.compactionChecker != null)
       this.compactionChecker.interrupt();
     if (this.healthCheckChore != null) {
@@ -1405,6 +1418,21 @@ public class  HRegionServer implements ClientProtocol,
     return instantiateHLog(rootDir, logName);
   }
 
+  private HLog getMetaWAL() throws IOException {
+    if (this.hlogForMeta == null) {
+      final String logName
+      = HLogUtil.getHLogDirectoryName(this.serverNameFromMasterPOV.toString());
+
+      Path logdir = new Path(rootDir, logName);
+      if (LOG.isDebugEnabled()) LOG.debug("logdir=" + logdir);
+
+      this.hlogForMeta = HLogFactory.createMetaHLog(this.fs.getBackingFs(), 
+          rootDir, logName, this.conf, getMetaWALActionListeners(), 
+          this.serverNameFromMasterPOV.toString());
+    }
+    return this.hlogForMeta;
+  }
+
   /**
    * Called by {@link #setupWALAndReplication()} creating WAL instance.
    * @param rootdir
@@ -1436,6 +1464,17 @@ public class  HRegionServer implements ClientProtocol,
     return listeners;
   }
 
+  protected List<WALActionsListener> getMetaWALActionListeners() {
+    List<WALActionsListener> listeners = new ArrayList<WALActionsListener>();
+    // Log roller.
+    this.metaHLogRoller = new MetaLogRoller(this, this);
+    String n = Thread.currentThread().getName();
+    Threads.setDaemonThreadRunning(this.metaHLogRoller.getThread(), 
+        n + ".META.logRoller", uncaughtExceptionHandler);
+    listeners.add(this.metaHLogRoller);
+    return listeners;
+  }
+
   protected LogRoller getLogRoller() {
     return hlogRoller;
   }
@@ -1465,12 +1504,6 @@ public class  HRegionServer implements ClientProtocol,
    */
   private void startServiceThreads() throws IOException {
     String n = Thread.currentThread().getName();
-    UncaughtExceptionHandler handler = new UncaughtExceptionHandler() {
-      public void uncaughtException(Thread t, Throwable e) {
-        abort("Uncaught exception in service thread " + t.getName(), e);
-      }
-    };
-
     // Start executor services
     this.service = new ExecutorService(getServerName().toString());
     this.service.startExecutorService(ExecutorType.RS_OPEN_REGION,
@@ -1486,14 +1519,15 @@ public class  HRegionServer implements ClientProtocol,
     this.service.startExecutorService(ExecutorType.RS_CLOSE_META,
       conf.getInt("hbase.regionserver.executor.closemeta.threads", 1));
 
-    Threads.setDaemonThreadRunning(this.hlogRoller.getThread(), n + ".logRoller", handler);
+    Threads.setDaemonThreadRunning(this.hlogRoller.getThread(), n + ".logRoller", uncaughtExceptionHandler);
     Threads.setDaemonThreadRunning(this.cacheFlusher.getThread(), n + ".cacheFlusher",
-      handler);
+      uncaughtExceptionHandler);
     Threads.setDaemonThreadRunning(this.compactionChecker.getThread(), n +
-      ".compactionChecker", handler);
+      ".compactionChecker", uncaughtExceptionHandler);
     if (this.healthCheckChore != null) {
     Threads
-        .setDaemonThreadRunning(this.healthCheckChore.getThread(), n + ".healthChecker", handler);
+        .setDaemonThreadRunning(this.healthCheckChore.getThread(), n + ".healthChecker", 
+            uncaughtExceptionHandler);
     }
 
     // Leases is not a Thread. Internally it runs a daemon thread. If it gets
@@ -1574,11 +1608,31 @@ public class  HRegionServer implements ClientProtocol,
       stop("One or more threads are no longer alive -- stop");
       return false;
     }
+    if (metaHLogRoller != null && !metaHLogRoller.isAlive()) {
+      stop("Meta HLog roller thread is no longer alive -- stop");
+      return false;
+    }
     return true;
   }
 
-  @Override
   public HLog getWAL() {
+    try {
+      return getWAL(null);
+    } catch (IOException e) {
+      LOG.warn("getWAL threw exception " + e);
+      return null; 
+    }
+  }
+
+  @Override
+  public HLog getWAL(HRegionInfo regionInfo) throws IOException {
+    //TODO: at some point this should delegate to the HLogFactory
+    //currently, we don't care about the region as much as we care about the 
+    //table.. (hence checking the tablename below)
+    if (regionInfo != null && 
+        Arrays.equals(regionInfo.getTableName(), HConstants.META_TABLE_NAME)) {
+      return getMetaWAL();
+    }
     return this.hlog;
   }
 
@@ -1725,6 +1779,9 @@ public class  HRegionServer implements ClientProtocol,
     if (this.hlogRoller != null) {
       Threads.shutdown(this.hlogRoller.getThread());
     }
+    if (this.metaHLogRoller != null) {
+      Threads.shutdown(this.metaHLogRoller.getThread());
+    }
     if (this.compactSplitThread != null) {
       this.compactSplitThread.join();
     }

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/LogRoller.java

@@ -24,6 +24,7 @@ import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hbase.*;
 import org.apache.hadoop.hbase.regionserver.wal.FailedLogCloseException;
+import org.apache.hadoop.hbase.regionserver.wal.HLog;
 import org.apache.hadoop.hbase.regionserver.wal.HLogKey;
 import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
 import org.apache.hadoop.hbase.regionserver.wal.WALActionsListener;
@@ -47,7 +48,7 @@ class LogRoller extends HasThread implements WALActionsListener {
   private final ReentrantLock rollLock = new ReentrantLock();
   private final AtomicBoolean rollLog = new AtomicBoolean(false);
   private final Server server;
-  private final RegionServerServices services;
+  protected final RegionServerServices services;
   private volatile long lastrolltime = System.currentTimeMillis();
   // Period to roll log.
   private final long rollperiod;
@@ -92,7 +93,7 @@ class LogRoller extends HasThread implements WALActionsListener {
       try {
         this.lastrolltime = now;
         // This is array of actual region names.
-        byte [][] regionsToFlush = this.services.getWAL().rollWriter(rollLog.get());
+        byte [][] regionsToFlush = getWAL().rollWriter(rollLog.get());
         if (regionsToFlush != null) {
           for (byte [] r: regionsToFlush) scheduleFlush(r);
         }
@@ -159,6 +160,10 @@ class LogRoller extends HasThread implements WALActionsListener {
     }
   }
 
+  protected HLog getWAL() throws IOException {
+    return this.services.getWAL(null);
+  }
+
   @Override
   public void preLogRoll(Path oldPath, Path newPath) throws IOException {
     // Not interested

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MetaLogRoller.java

@@ -0,0 +1,37 @@
+/**
+ * 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.hbase.regionserver;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hbase.HConstants;
+import org.apache.hadoop.hbase.HRegionInfo;
+import org.apache.hadoop.hbase.Server;
+import org.apache.hadoop.hbase.regionserver.wal.HLog;
+
+@InterfaceAudience.Private
+class MetaLogRoller extends LogRoller {
+  public MetaLogRoller(Server server, RegionServerServices services) {
+    super(server, services);
+  }
+  @Override
+  protected HLog getWAL() throws IOException {
+    return services.getWAL(HRegionInfo.FIRST_META_REGIONINFO);
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionServerServices.java

@@ -23,6 +23,7 @@ import java.util.concurrent.ConcurrentMap;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.hbase.HRegionInfo;
 import org.apache.hadoop.hbase.catalog.CatalogTracker;
 import org.apache.hadoop.hbase.ipc.RpcServer;
 import org.apache.hadoop.hbase.regionserver.wal.HLog;
@@ -38,8 +39,9 @@ public interface RegionServerServices extends OnlineRegions {
    */
   public boolean isStopping();
 
-  /** @return the HLog */
+  /** @return the HLog for a particular region. Pass null for getting the 
-  public HLog getWAL();
+   * default (common) WAL */
+  public HLog getWAL(HRegionInfo regionInfo) throws IOException;
 
   /**
    * @return Implementation of {@link CompactionRequestor} or null.

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/OpenRegionHandler.java

@@ -31,6 +31,7 @@ import org.apache.hadoop.hbase.executor.EventHandler;
 import org.apache.hadoop.hbase.regionserver.HRegion;
 import org.apache.hadoop.hbase.regionserver.RegionServerAccounting;
 import org.apache.hadoop.hbase.regionserver.RegionServerServices;
+import org.apache.hadoop.hbase.regionserver.wal.HLog;
 import org.apache.hadoop.hbase.util.CancelableProgressable;
 import org.apache.hadoop.hbase.zookeeper.ZKAssign;
 import org.apache.zookeeper.KeeperException;
@@ -44,7 +45,7 @@ import org.apache.zookeeper.KeeperException;
 public class OpenRegionHandler extends EventHandler {
   private static final Log LOG = LogFactory.getLog(OpenRegionHandler.class);
 
-  private final RegionServerServices rsServices;
+  protected final RegionServerServices rsServices;
 
   private final HRegionInfo regionInfo;
   private final HTableDescriptor htd;
@@ -424,7 +425,8 @@ public class OpenRegionHandler extends EventHandler {
       // Instantiate the region.  This also periodically tickles our zk OPENING
       // state so master doesn't timeout this region in transition.
       region = HRegion.openHRegion(this.regionInfo, this.htd,
-          this.rsServices.getWAL(), this.server.getConfiguration(),
+          this.rsServices.getWAL(this.regionInfo), 
+          this.server.getConfiguration(),
           this.rsServices,
         new CancelableProgressable() {
           public boolean progress() {

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/FSHLog.java

@@ -154,6 +154,8 @@ class FSHLog implements HLog, Syncable {
 
   private final AtomicLong logSeqNum = new AtomicLong(0);
 
+  private boolean forMeta = false;
+
   // The timestamp (in ms) when the log file was created.
   private volatile long filenum = -1;
 
@@ -211,15 +213,15 @@ class FSHLog implements HLog, Syncable {
    *
    * @param fs filesystem handle
    * @param root path for stored and archived hlogs
-   * @param logName dir where hlogs are stored
+   * @param logDir dir where hlogs are stored
    * @param conf configuration to use
    * @throws IOException
    */
-  public FSHLog(final FileSystem fs, final Path root, final String logName,
+  public FSHLog(final FileSystem fs, final Path root, final String logDir,
                 final Configuration conf)
   throws IOException {
-    this(fs, root, logName, HConstants.HREGION_OLDLOGDIR_NAME, 
+    this(fs, root, logDir, HConstants.HREGION_OLDLOGDIR_NAME, 
-        conf, null, true, null);
+        conf, null, true, null, false);
   }
   
   /**
@@ -227,16 +229,16 @@ class FSHLog implements HLog, Syncable {
    *
    * @param fs filesystem handle
    * @param root path for stored and archived hlogs
-   * @param logName dir where hlogs are stored
+   * @param logDir dir where hlogs are stored
-   * @param oldLogName dir where hlogs are archived
+   * @param oldLogDir dir where hlogs are archived
    * @param conf configuration to use
    * @throws IOException
    */
-  public FSHLog(final FileSystem fs, final Path root, final String logName,
+  public FSHLog(final FileSystem fs, final Path root, final String logDir,
-                final String oldLogName, final Configuration conf)
+                final String oldLogDir, final Configuration conf)
   throws IOException {
-    this(fs, root, logName, oldLogName, 
+    this(fs, root, logDir, oldLogDir, 
-        conf, null, true, null);
+        conf, null, true, null, false);
   }
 
   /**
@@ -248,7 +250,7 @@ class FSHLog implements HLog, Syncable {
    *
    * @param fs filesystem handle
    * @param root path for stored and archived hlogs
-   * @param logName dir where hlogs are stored
+   * @param logDir dir where hlogs are stored
    * @param conf configuration to use
    * @param listeners Listeners on WAL events. Listeners passed here will
    * be registered before we do anything else; e.g. the
@@ -258,11 +260,11 @@ class FSHLog implements HLog, Syncable {
    *        If prefix is null, "hlog" will be used
    * @throws IOException
    */
-  public FSHLog(final FileSystem fs, final Path root, final String logName,
+  public FSHLog(final FileSystem fs, final Path root, final String logDir,
       final Configuration conf, final List<WALActionsListener> listeners,
       final String prefix) throws IOException {
-    this(fs, root, logName, HConstants.HREGION_OLDLOGDIR_NAME, 
+    this(fs, root, logDir, HConstants.HREGION_OLDLOGDIR_NAME, 
-        conf, listeners, true, prefix);
+        conf, listeners, true, prefix, false);
   }
 
   /**
@@ -274,7 +276,8 @@ class FSHLog implements HLog, Syncable {
    *
    * @param fs filesystem handle
    * @param root path to where logs and oldlogs
-   * @param oldLogName path to where hlogs are archived
+   * @param logDir dir where hlogs are stored
+   * @param oldLogDir dir where hlogs are archived
    * @param conf configuration to use
    * @param listeners Listeners on WAL events. Listeners passed here will
    * be registered before we do anything else; e.g. the
@@ -283,18 +286,20 @@ class FSHLog implements HLog, Syncable {
    * @param prefix should always be hostname and port in distributed env and
    *        it will be URL encoded before being used.
    *        If prefix is null, "hlog" will be used
+   * @param forMeta if this hlog is meant for meta updates
    * @throws IOException
    */
-  private FSHLog(final FileSystem fs, final Path root, final String logName,
+  public FSHLog(final FileSystem fs, final Path root, final String logDir,
-      final String oldLogName, final Configuration conf, 
+      final String oldLogDir, final Configuration conf, 
       final List<WALActionsListener> listeners,
-      final boolean failIfLogDirExists, final String prefix)
+      final boolean failIfLogDirExists, final String prefix, boolean forMeta)
   throws IOException {
     super();
     this.fs = fs;
     this.rootDir = root;
-    this.dir = new Path(this.rootDir, logName);
+    this.dir = new Path(this.rootDir, logDir);
-    this.oldLogDir = new Path(this.rootDir, oldLogName);
+    this.oldLogDir = new Path(this.rootDir, oldLogDir);
+    this.forMeta = forMeta;
     this.conf = conf;
    
     if (listeners != null) {
@@ -333,15 +338,16 @@ class FSHLog implements HLog, Syncable {
     // If prefix is null||empty then just name it hlog
     this.prefix = prefix == null || prefix.isEmpty() ?
         "hlog" : URLEncoder.encode(prefix, "UTF8");
-   
+
-    if (failIfLogDirExists && this.fs.exists(dir)) {
+    boolean dirExists = false;
+    if (failIfLogDirExists && (dirExists = this.fs.exists(dir))) {
       throw new IOException("Target HLog directory already exists: " + dir);
     }
-    if (!fs.mkdirs(dir)) {
+    if (!dirExists && !fs.mkdirs(dir)) {
       throw new IOException("Unable to mkdir " + dir);
     }
 
-    if (!fs.exists(oldLogDir)) {
+    if (!fs.exists(this.oldLogDir)) {
       if (!fs.mkdirs(this.oldLogDir)) {
         throw new IOException("Unable to mkdir " + this.oldLogDir);
       }
@@ -483,6 +489,7 @@ class FSHLog implements HLog, Syncable {
       long currentFilenum = this.filenum;
       Path oldPath = null;
       if (currentFilenum > 0) {
+        //computeFilename  will take care of meta hlog filename
         oldPath = computeFilename(currentFilenum);
       }
       this.filenum = System.currentTimeMillis();
@@ -561,6 +568,9 @@ class FSHLog implements HLog, Syncable {
    */
   protected Writer createWriterInstance(final FileSystem fs, final Path path,
       final Configuration conf) throws IOException {
+    if (forMeta) {
+      //TODO: set a higher replication for the hlog files (HBASE-6773)
+    }
     return HLogFactory.createWriter(fs, path, conf);
   }
 
@@ -729,7 +739,11 @@ class FSHLog implements HLog, Syncable {
     if (filenum < 0) {
       throw new RuntimeException("hlog file number can't be < 0");
     }
-    return new Path(dir, prefix + "." + filenum);
+    String child = prefix + "." + filenum;
+    if (forMeta) {
+      child += HLog.META_HLOG_FILE_EXTN;
+    }
+    return new Path(dir, child);
   }
 
   @Override

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/HLog.java

@@ -50,6 +50,8 @@ public interface HLog {
   /** File Extension used while splitting an HLog into regions (HBASE-2312) */
   public static final String SPLITTING_EXT = "-splitting";
   public static final boolean SPLIT_SKIP_ERRORS_DEFAULT = false;
+  /** The META region's HLog filename extension */
+  public static final String META_HLOG_FILE_EXTN = ".meta";
 
   /*
    * Name of directory that holds recovered edits written by the wal log

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/HLogFactory.java

@@ -26,9 +26,9 @@ import java.util.List;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.regionserver.wal.HLog.Reader;
 import org.apache.hadoop.hbase.regionserver.wal.HLog.Writer;
 
@@ -50,6 +50,13 @@ public class HLogFactory {
         final String prefix) throws IOException {
       return new FSHLog(fs, root, logName, conf, listeners, prefix);
     }
+
+    public static HLog createMetaHLog(final FileSystem fs, final Path root, final String logName,
+        final Configuration conf, final List<WALActionsListener> listeners,
+        final String prefix) throws IOException {
+      return new FSHLog(fs, root, logName, HConstants.HREGION_OLDLOGDIR_NAME, 
+            conf, listeners, false, prefix, true);
+    }
     
     /*
      * WAL Reader

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/HLogSplitter.java

@@ -49,6 +49,7 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.PathFilter;
 import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.HTableDescriptor;
 import org.apache.hadoop.hbase.RemoteExceptionHandler;
@@ -302,6 +303,11 @@ public class HLogSplitter {
             + ": " + logPath + ", length=" + logLength);
         Reader in = null;
         try {
+          //actually, for meta-only hlogs, we don't need to go thru the process
+          //of parsing and segregating by regions since all the logs are for
+          //meta only. However, there is a sequence number that can be obtained
+          //only by parsing.. so we parse for all files currently
+          //TODO: optimize this part somehow
           in = getReader(fs, log, conf, skipErrors);
           if (in != null) {
             parseHLog(in, logPath, entryBuffers, fs, conf, skipErrors);

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/HLogUtil.java

@@ -76,7 +76,8 @@ public class HLogUtil {
   /**
    * Pattern used to validate a HLog file name
    */
-  private static final Pattern pattern = Pattern.compile(".*\\.\\d*");
+  private static final Pattern pattern = 
+      Pattern.compile(".*\\.\\d*("+HLog.META_HLOG_FILE_EXTN+")*");
 
   /**
    * @param filename
@@ -312,4 +313,11 @@ public class HLogUtil {
     }
     return filesSorted;
   }
+
+  public static boolean isMetaFile(Path p) {
+    if (p.getName().endsWith(HLog.META_HLOG_FILE_EXTN)) {
+      return true;
+    }
+    return false;
+  }
 }

hbase-server/src/test/java/org/apache/hadoop/hbase/master/MockRegionServer.java

@@ -273,12 +273,6 @@ class MockRegionServer implements AdminProtocol, ClientProtocol, RegionServerSer
     return false;
   }
 
-  @Override
-  public HLog getWAL() {
-    // TODO Auto-generated method stub
-    return null;
-  }
-
   @Override
   public CompactionRequestor getCompactionRequester() {
     // TODO Auto-generated method stub
@@ -499,4 +493,10 @@ class MockRegionServer implements AdminProtocol, ClientProtocol, RegionServerSer
     // TODO Auto-generated method stub
     return null;
   }
+
+  @Override
+  public HLog getWAL(HRegionInfo regionInfo) throws IOException {
+    // TODO Auto-generated method stub
+    return null;
+  }
 }

hbase-server/src/test/java/org/apache/hadoop/hbase/util/MockRegionServerServices.java

@@ -25,6 +25,7 @@ import java.util.concurrent.ConcurrentSkipListMap;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.hbase.HRegionInfo;
 import org.apache.hadoop.hbase.ServerName;
 import org.apache.hadoop.hbase.catalog.CatalogTracker;
 import org.apache.hadoop.hbase.fs.HFileSystem;
@@ -88,11 +89,6 @@ public class MockRegionServerServices implements RegionServerServices {
     return this.stopping;
   }
 
-  @Override
-  public HLog getWAL() {
-    return null;
-  }
-
   @Override
   public RpcServer getRpcServer() {
     return null;
@@ -170,4 +166,10 @@ public class MockRegionServerServices implements RegionServerServices {
   public Leases getLeases() {
     return null;
   }
+
+  @Override
+  public HLog getWAL(HRegionInfo regionInfo) throws IOException {
+    // TODO Auto-generated method stub
+    return null;
+  }
 }