HADOOP-2443 Keep lazy cache of regions in client rather than an 'authoritative' list

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/trunk/src/contrib/hbase@611727 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -38,6 +38,8 @@ Trunk (unreleased changes)
    HADOOP-2407 Keeping MapFile.Reader open is expensive: Part 2
    HADOOP-2533 Performance: Scanning, just creating MapWritable in next
                consumes >20% CPU
+   HADOOP-2443 Keep lazy cache of regions in client rather than an
+               'authoritative' list (Bryan Duxbury via Stack)
 
   BUG FIXES
    HADOOP-2059 In tests, exceptions in min dfs shutdown should not fail test

src/java/org/apache/hadoop/hbase/HBaseAdmin.java

@@ -117,7 +117,7 @@ public class HBaseAdmin implements HConstants {
     for (int tries = 0; tries < numRetries; tries++) {
       try {
         // Wait for new table to come on-line
-        connection.getTableServers(desc.getName());
+        connection.locateRegion(desc.getName(), EMPTY_START_ROW);
         break;
         
       } catch (TableNotFoundException e) {
@@ -541,9 +541,7 @@ public class HBaseAdmin implements HConstants {
   
   private HRegionLocation getFirstMetaServerForTable(Text tableName)
   throws IOException {
-    SortedMap<Text, HRegionLocation> metaservers =
+    Text tableKey = new Text(tableName.toString() + ",,99999999999999");
-      connection.getTableServers(META_TABLE_NAME); 
+    return connection.locateRegion(META_TABLE_NAME, tableKey);
-    return metaservers.get((metaservers.containsKey(tableName)) ?
-        tableName : metaservers.headMap(tableName).lastKey());
   }
 }

src/java/org/apache/hadoop/hbase/HConnection.java

@@ -57,24 +57,26 @@ public interface HConnection {
   public HTableDescriptor[] listTables() throws IOException;
   
   /**
-   * Gets the servers of the given table.
+   * Find the location of the region of <i>tableName</i> that <i>row</i>
-   * 
+   * lives in.
-   * @param tableName - the table to be located
+   * @param tableName name of the table <i>row</i> is in
-   * @return map of startRow -> RegionLocation
+   * @param row row key you're trying to find the region of
-   * @throws IOException - if the table can not be located after retrying
+   * @return HRegionLocation that describes where to find the reigon in 
+   * question
    */
-  public SortedMap<Text, HRegionLocation> getTableServers(Text tableName)
+  public HRegionLocation locateRegion(Text tableName, Text row)
   throws IOException;
   
   /**
-   * Reloads servers for the specified table.
+   * Find the location of the region of <i>tableName</i> that <i>row</i>
-   * 
+   * lives in, ignoring any value that might be in the cache.
-   * @param tableName name of table whose servers are to be reloaded
+   * @param tableName name of the table <i>row</i> is in
-   * @return map of start key -> RegionLocation
+   * @param row row key you're trying to find the region of
-   * @throws IOException
+   * @return HRegionLocation that describes where to find the reigon in 
+   * question
    */
-  public SortedMap<Text, HRegionLocation>
+  public HRegionLocation relocateRegion(Text tableName, Text row)
-  reloadTableServers(final Text tableName) throws IOException;
+  throws IOException;  
   
   /** 
    * Establishes a connection to the region server at the specified address.

src/java/org/apache/hadoop/hbase/HConnectionManager.java

@@ -95,11 +95,10 @@ public class HConnectionManager implements HConstants {
     }    
   }
   
-  /* encapsulates finding the servers for an HBase instance */
+  /* Encapsulates finding the servers for an HBase instance */
   private static class TableServers implements HConnection, HConstants {
     private static final Log LOG = LogFactory.getLog(TableServers.class);
     private final Class<? extends HRegionInterface> serverInterfaceClass;
-    private final long threadWakeFrequency;
     private final long pause;
     private final int numRetries;
 
@@ -110,21 +109,20 @@ public class HConnectionManager implements HConstants {
     
     private final Integer rootRegionLock = new Integer(0);
     private final Integer metaRegionLock = new Integer(0);
+    private final Integer userRegionLock = new Integer(0);
         
     private volatile HBaseConfiguration conf;
 
-    // Map tableName -> (Map startRow -> (HRegionInfo, HServerAddress)
-    private Map<Text, SortedMap<Text, HRegionLocation>> tablesToServers;
-    
     // Set of closed tables
     private Set<Text> closedTables;
     
-    // Set of tables currently being located
-    private Set<Text> tablesBeingLocated;
-
     // Known region HServerAddress.toString() -> HRegionInterface 
     private Map<String, HRegionInterface> servers;
 
+    private HRegionLocation rootRegionLocation; 
+    
+    private Map<Text, SortedMap<Text, HRegionLocation>> cachedRegionLocations;
+    
     /** 
      * constructor
      * @param conf Configuration object
@@ -147,20 +145,15 @@ public class HConnectionManager implements HConstants {
             "Unable to find region server interface " + serverClassName, e);
       }
 
-      this.threadWakeFrequency = conf.getLong(THREAD_WAKE_FREQUENCY, 10 * 1000);
       this.pause = conf.getLong("hbase.client.pause", 30 * 1000);
       this.numRetries = conf.getInt("hbase.client.retries.number", 5);
       
       this.master = null;
       this.masterChecked = false;
 
-      this.tablesToServers = 
+      this.cachedRegionLocations = 
         new ConcurrentHashMap<Text, SortedMap<Text, HRegionLocation>>();
-      
       this.closedTables = Collections.synchronizedSet(new HashSet<Text>());
-      this.tablesBeingLocated = Collections.synchronizedSet(
-          new HashSet<Text>());
-      
       this.servers = new ConcurrentHashMap<String, HRegionInterface>();
     }
     
@@ -246,18 +239,30 @@ public class HConnectionManager implements HConstants {
     /** {@inheritDoc} */
     public HTableDescriptor[] listTables() throws IOException {
       HashSet<HTableDescriptor> uniqueTables = new HashSet<HTableDescriptor>();
+      long scannerId = -1L;
+      HRegionInterface server = null;
       
-      SortedMap<Text, HRegionLocation> metaTables =
+      Text startRow = EMPTY_START_ROW;
-        getTableServers(META_TABLE_NAME);
+      HRegionLocation metaLocation = null;
 
-      for (HRegionLocation t: metaTables.values()) {
+      // scan over the each meta region
-        HRegionInterface server = getHRegionConnection(t.getServerAddress());
+      do {
-        long scannerId = -1L;
+        try{
-        try {
+          // turn the start row into a location
-          scannerId = server.openScanner(t.getRegionInfo().getRegionName(),
+          metaLocation = 
-              COLUMN_FAMILY_ARRAY, EMPTY_START_ROW, System.currentTimeMillis(),
+            locateRegion(META_TABLE_NAME, startRow);
-              null);
 
+          // connect to the server hosting the .META. region
+          server = 
+            getHRegionConnection(metaLocation.getServerAddress());
+
+          // open a scanner over the meta region
+          scannerId = server.openScanner(
+            metaLocation.getRegionInfo().getRegionName(),
+            COLUMN_FAMILY_ARRAY, EMPTY_START_ROW, LATEST_TIMESTAMP,
+            null);
+          
+          // iterate through the scanner, accumulating unique table names
           while (true) {
             HbaseMapWritable values = server.next(scannerId);
             if (values == null || values.size() == 0) {
@@ -277,78 +282,330 @@ public class HConnectionManager implements HConstants {
               }
             }
           }
-        } catch (RemoteException ex) {
-          throw RemoteExceptionHandler.decodeRemoteException(ex);
           
-        } finally {
+          server.close(scannerId);
+          scannerId = -1L;
+          
+          // advance the startRow to the end key of the current region
+          startRow = metaLocation.getRegionInfo().getEndKey();          
+        } catch (IOException e) {
+          // need retry logic?
+          throw e;
+        }
+        finally {
           if (scannerId != -1L) {
             server.close(scannerId);
           }
         }
-      }
+      } while (startRow.compareTo(EMPTY_START_ROW) != 0);
+      
       return uniqueTables.toArray(new HTableDescriptor[uniqueTables.size()]);
     }
 
-    /** {@inheritDoc} */
+    public HRegionLocation locateRegion(Text tableName, Text row)
-    public SortedMap<Text, HRegionLocation> getTableServers(Text tableName)
+    throws IOException{
-    throws IOException {
+      return locateRegion(tableName, row, true);
+    }
 
+    public HRegionLocation relocateRegion(Text tableName, Text row)
+    throws IOException{
+      return locateRegion(tableName, row, false);
+    }
+
+    private HRegionLocation locateRegion(Text tableName, Text row, 
+      boolean useCache)
+    throws IOException{
       if (tableName == null || tableName.getLength() == 0) {
         throw new IllegalArgumentException(
             "table name cannot be null or zero length");
       }
             
-      closedTables.remove(tableName);
+      if (tableName.equals(ROOT_TABLE_NAME)) {
+        synchronized (rootRegionLock) {
+          // This block guards against two threads trying to find the root
+          // region at the same time. One will go do the find while the 
+          // second waits. The second thread will not do find.
           
-      SortedMap<Text, HRegionLocation> tableServers  =
+          if (!useCache || rootRegionLocation == null) {
-        tablesToServers.get(tableName);
+            return locateRootRegion();
-      
+          }
-      if (tableServers == null ) {
+          return rootRegionLocation;
-        if (LOG.isDebugEnabled()) {
+        }        
-          LOG.debug("No servers for " + tableName + ". Doing a find...");
+      } else if (tableName.equals(META_TABLE_NAME)) {
+        synchronized (metaRegionLock) {
+          // This block guards against two threads trying to load the meta 
+          // region at the same time. The first will load the meta region and
+          // the second will use the value that the first one found.
+
+          return locateRegionInMeta(ROOT_TABLE_NAME, tableName, row, useCache);
+        }
+      } else {
+        synchronized(userRegionLock){
+          return locateRegionInMeta(META_TABLE_NAME, tableName, row, useCache);
         }
-        // We don't know where the table is.
-        // Load the information from meta.
-        tableServers = findServersForTable(tableName);
       }
-      SortedMap<Text, HRegionLocation> servers =
-        new TreeMap<Text, HRegionLocation>();
-      servers.putAll(tableServers);
-      return servers;
     }
 
-    /** {@inheritDoc} */
+    /**
-    public SortedMap<Text, HRegionLocation>
+      * Convenience method for turning a MapWritable into the underlying
-    reloadTableServers(final Text tableName) throws IOException {
+      * SortedMap we all know and love.
-      closedTables.remove(tableName);
+      */
-      SortedMap<Text, HRegionLocation> tableServers =
+    private SortedMap<Text, byte[]> sortedMapFromMapWritable(
-        new TreeMap<Text, HRegionLocation>();
+      HbaseMapWritable writable) {
-      // Reload information for the whole table
+      SortedMap<Text, byte[]> results = new TreeMap<Text, byte[]>();
-      tableServers.putAll(findServersForTable(tableName));
+      for (Map.Entry<Writable, Writable> e: writable.entrySet()) {
-      if (LOG.isDebugEnabled()) {
+        HStoreKey key = (HStoreKey) e.getKey();
-        StringBuilder sb = new StringBuilder();
+        results.put(key.getColumn(), 
-        int count = 0;
+          ((ImmutableBytesWritable) e.getValue()).get());
-        for (HRegionLocation location: tableServers.values()) {
-          if (sb.length() > 0) {
-            sb.append(" ");
-          }
-          sb.append(count++);
-          sb.append(". ");
-          sb.append("address=");
-          sb.append(location.getServerAddress());
-          sb.append(", ");
-          sb.append(location.getRegionInfo().getRegionName());
-        }
-        LOG.debug("Result of findTable on " + tableName.toString() +
-          ": " + sb.toString());
       }
       
-      return tableServers;
+      return results;
+    }
+
+    /**
+      * Search one of the meta tables (-ROOT- or .META.) for the HRegionLocation
+      * info that contains the table and row we're seeking.
+      */
+    private HRegionLocation locateRegionInMeta(Text parentTable,
+      Text tableName, Text row, boolean useCache)
+    throws IOException{
+      HRegionLocation location = null;
+      
+      // if we're supposed to be using the cache, then check it for a possible
+      // hit. otherwise, delete any existing cached location so it won't 
+      // interfere.
+      if (useCache) {
+        location = getCachedLocation(tableName, row);
+        if (location != null) {
+          LOG.debug("Looking in " + parentTable + " for " 
+            + tableName + "/" + row
+            + ", got a cache hit with " 
+            + location.getRegionInfo().getRegionName());
+          return location;
+        }
+      } else{
+        deleteCachedLocation(tableName, row);
+      }
+
+      // build the key of the meta region we should be looking for.
+      // the extra 9's on the end are necessary to allow "exact" matches
+      // without knowing the precise region names.
+      Text metaKey = new Text(tableName.toString() + "," 
+        + row.toString() + ",999999999999999");
+
+      int tries = 0;
+      while (true) {
+        tries++;
+        
+        if (tries >= numRetries) {
+          throw new NoServerForRegionException("Unable to find region for " 
+            + row + " after " + numRetries + " tries.");
+        }
+
+        try{
+          // locate the root region
+          HRegionLocation metaLocation = locateRegion(parentTable, metaKey);
+          HRegionInterface server = 
+            getHRegionConnection(metaLocation.getServerAddress());
+
+          // query the root region for the location of the meta region
+          HbaseMapWritable regionInfoRow = server.getClosestRowBefore(
+            metaLocation.getRegionInfo().getRegionName(), 
+            metaKey, HConstants.LATEST_TIMESTAMP);
+
+          // convert the MapWritable into a Map we can use
+          SortedMap<Text, byte[]> results = 
+            sortedMapFromMapWritable(regionInfoRow);
+
+          byte[] bytes = results.get(COL_REGIONINFO);
+
+          if (bytes == null || bytes.length == 0) {
+            throw new IOException("HRegionInfo was null or empty in " + 
+              parentTable);
+          }
+
+          // convert the row result into the HRegionLocation we need!
+          HRegionInfo regionInfo = (HRegionInfo) Writables.getWritable(
+              results.get(COL_REGIONINFO), new HRegionInfo());
+
+          if (regionInfo.isOffline()) {
+            throw new IllegalStateException("region offline: " + 
+              regionInfo.getRegionName());
+          }
+
+          // possible we got a region of a different table...
+          if (!regionInfo.getTableDesc().getName().equals(tableName)) {
+            throw new TableNotFoundException(
+              "Table '" + tableName + "' was not found.");
+          }
+
+          String serverAddress = 
+            Writables.bytesToString(results.get(COL_SERVER));
+        
+          if (serverAddress.equals("")) { 
+            throw new NoServerForRegionException(
+              "No server address listed in " + parentTable + " for region "
+              + regionInfo.getRegionName());
+          }
+        
+          // instantiate the location
+          location = new HRegionLocation(regionInfo, 
+            new HServerAddress(serverAddress));
+      
+          cacheLocation(tableName, location);
+
+          return location;
+        } catch (IllegalStateException e) {
+          if (tries < numRetries - 1) {
+            if (LOG.isDebugEnabled()) {
+              LOG.debug("reloading table servers because: " + e.getMessage());
+            }
+            relocateRegion(parentTable, metaKey);
+          } else {
+            throw e;
+          }
+        } catch (IOException e) {
+          if (e instanceof RemoteException) {
+            e = RemoteExceptionHandler.decodeRemoteException(
+                (RemoteException) e);
+          }
+          if (tries < numRetries - 1) {
+            if (LOG.isDebugEnabled()) {
+              LOG.debug("reloading table servers because: " + e.getMessage());
+            }
+            relocateRegion(parentTable, metaKey);
+          } else {
+            throw e;
+          }
+        }
+      
+        try{
+          Thread.sleep(pause);              
+        } catch (InterruptedException e){
+          // continue
+        }
+      }
+    }
+
+    /** 
+      * Search the cache for a location that fits our table and row key.
+      * Return null if no suitable region is located. TODO: synchronization note
+      */
+    private HRegionLocation getCachedLocation(Text tableName, Text row) {
+      // find the map of cached locations for this table
+      SortedMap<Text, HRegionLocation> tableLocations = 
+        cachedRegionLocations.get(tableName);
+
+      // if tableLocations for this table isn't built yet, make one
+      if (tableLocations == null) {
+        tableLocations = new TreeMap<Text, HRegionLocation>();
+        cachedRegionLocations.put(tableName, tableLocations);
+      }
+
+      // start to examine the cache. we can only do cache actions
+      // if there's something in the cache for this table.
+      if (!tableLocations.isEmpty()) {
+        if (tableLocations.containsKey(row)) {
+          return tableLocations.get(row);
+        }
+        
+        // cut the cache so that we only get the part that could contain
+        // regions that match our key
+        SortedMap<Text, HRegionLocation> matchingRegions =
+          tableLocations.headMap(row);
+
+        // if that portion of the map is empty, then we're done. otherwise,
+        // we need to examine the cached location to verify that it is 
+        // a match by end key as well.
+        if (!matchingRegions.isEmpty()) {
+          HRegionLocation possibleRegion = 
+            matchingRegions.get(matchingRegions.lastKey());
+          
+          Text endKey = possibleRegion.getRegionInfo().getEndKey();
+          
+          // make sure that the end key is greater than the row we're looking 
+          // for, otherwise the row actually belongs in the next region, not 
+          // this one. the exception case is when the endkey is EMPTY_START_ROW,
+          // signifying that the region we're checking is actually the last 
+          // region in the table.
+          if (endKey.equals(EMPTY_TEXT) || endKey.compareTo(row) > 0) {
+            return possibleRegion;
+          }
+        }
+      }
+      
+      // passed all the way through, so we got nothin - complete cache miss
+      return null;
+    }
+
+
+    /**
+      * Delete a cached location, if it satisfies the table name and row
+      * requirements.
+      */
+    private void deleteCachedLocation(Text tableName, Text row){
+      // find the map of cached locations for this table
+      SortedMap<Text, HRegionLocation> tableLocations = 
+        cachedRegionLocations.get(tableName);
+
+      // if tableLocations for this table isn't built yet, make one
+      if (tableLocations == null) {
+        tableLocations = new TreeMap<Text, HRegionLocation>();
+        cachedRegionLocations.put(tableName, tableLocations);
+      }
+
+      // start to examine the cache. we can only do cache actions
+      // if there's something in the cache for this table.
+      if (!tableLocations.isEmpty()) {
+        // cut the cache so that we only get the part that could contain
+        // regions that match our key
+        SortedMap<Text, HRegionLocation> matchingRegions =
+          tableLocations.headMap(row);
+
+        // if that portion of the map is empty, then we're done. otherwise,
+        // we need to examine the cached location to verify that it is 
+        // a match by end key as well.
+        if (!matchingRegions.isEmpty()) {
+          HRegionLocation possibleRegion = 
+            matchingRegions.get(matchingRegions.lastKey());
+          
+          Text endKey = possibleRegion.getRegionInfo().getEndKey();
+          
+          // by nature of the map, we know that the start key has to be < 
+          // otherwise it wouldn't be in the headMap. 
+          if (endKey.compareTo(row) <= 0) {
+            // delete any matching entry
+            tableLocations.remove(matchingRegions.lastKey());
+          }
+        }
+      }      
+    }
+
+
+    /**
+      * Put a newly discovered HRegionLocation into the cache.
+      */
+    private void cacheLocation(Text tableName, HRegionLocation location){
+      Text startKey = location.getRegionInfo().getStartKey();
+      
+      // find the map of cached locations for this table
+      SortedMap<Text, HRegionLocation> tableLocations = 
+        cachedRegionLocations.get(tableName);
+
+      // if tableLocations for this table isn't built yet, make one
+      if (tableLocations == null) {
+        tableLocations = new TreeMap<Text, HRegionLocation>();
+        cachedRegionLocations.put(tableName, tableLocations);
+      }
+      
+      // save the HRegionLocation under the startKey
+      tableLocations.put(startKey, location);
     }
     
     /** {@inheritDoc} */
     public HRegionInterface getHRegionConnection(
-        HServerAddress regionServer) throws IOException {
+      HServerAddress regionServer) 
+    throws IOException {
 
       HRegionInterface server;
       synchronized (this.servers) {
@@ -396,186 +653,52 @@ public class HConnectionManager implements HConstants {
         return;
       }
 
-      SortedMap<Text, HRegionLocation> tableServers =
-        tablesToServers.remove(tableName);
-
-      if (tableServers == null) {
-        // Table not open. Ignore it.
-        return;
-      }
-      
       closedTables.add(tableName);
 
-      // Shut down connections to the HRegionServers
+      if (cachedRegionLocations.containsKey(tableName)) {
+        SortedMap<Text, HRegionLocation> tableServers = 
+          cachedRegionLocations.remove(tableName);
 
-      synchronized (this.servers) {
+        // Shut down connections to the HRegionServers
-        for (HRegionLocation r: tableServers.values()) {
+        synchronized (this.servers) {
-          this.servers.remove(r.getServerAddress().toString());
+          for (HRegionLocation r: tableServers.values()) {
+            this.servers.remove(r.getServerAddress().toString());
+          }
         }
       }
     }
     
+    /** Convenience method for closing all open tables.*/
     void closeAll() {
       this.closed = true;
-      ArrayList<Text> tables = new ArrayList<Text>(tablesToServers.keySet());
+      ArrayList<Text> tables = 
+        new ArrayList<Text>(cachedRegionLocations.keySet());
       for (Text tableName: tables) {
         close(tableName);
       }
     }
     
-    /*
-     * Clears the cache of all known information about the specified table and
-     * locates a table by searching the META or ROOT region (as appropriate) or
-     * by querying the master for the location of the root region if that is the
-     * table requested.
-     * 
-     * @param tableName - name of table to find servers for
-     * @return - map of first row to table info for all regions in the table
-     * @throws IOException
-     */
-    private SortedMap<Text, HRegionLocation> findServersForTable(Text tableName)
-    throws IOException {
-      
-      // Wipe out everything we know about this table
-      if (this.tablesToServers.remove(tableName) != null) {
-        if (LOG.isDebugEnabled()) {
-          LOG.debug("Wiping out all we know of " + tableName);
-        }
-      }
-      
-      SortedMap<Text, HRegionLocation> srvrs =
-        new TreeMap<Text, HRegionLocation>();
-      
-      if (tableName.equals(ROOT_TABLE_NAME)) {
-        synchronized (rootRegionLock) {
-          // This block guards against two threads trying to find the root
-          // region at the same time. One will go do the find while the 
-          // second waits. The second thread will not do find.
-          
-          srvrs = this.tablesToServers.get(ROOT_TABLE_NAME);
-          
-          if (srvrs == null) {
-            srvrs = locateRootRegion();
-          }
-          this.tablesToServers.put(tableName, srvrs);
-        }
-        
-      } else if (tableName.equals(META_TABLE_NAME)) {
-        synchronized (metaRegionLock) {
-          // This block guards against two threads trying to load the meta 
-          // region at the same time. The first will load the meta region and
-          // the second will use the value that the first one found.
-          
-          SortedMap<Text, HRegionLocation> rootServers =
-            tablesToServers.get(ROOT_TABLE_NAME);
-          
-          for (boolean refindRoot = true; refindRoot; ) {
-            if (rootServers == null || rootServers.size() == 0) {
-              // (re)find the root region
-              rootServers = findServersForTable(ROOT_TABLE_NAME);
-              // but don't try again
-              refindRoot = false;
-            }
-            try {
-              srvrs = getTableServers(rootServers, META_TABLE_NAME);
-              break;
-              
-            } catch (NotServingRegionException e) {
-              if (!refindRoot) {
-                // Already found root once. Give up.
-                throw e;
-              }
-              // The root region must have moved - refind it
-              rootServers.clear();
-            }
-          }
-          this.tablesToServers.put(tableName, srvrs);
-        }
-      } else {
-        boolean waited = false;
-        synchronized (this.tablesBeingLocated) {
-          // This block ensures that only one thread will actually try to
-          // find a table. If a second thread comes along it will wait
-          // until the first thread finishes finding the table.
-          
-          while (this.tablesBeingLocated.contains(tableName)) {
-            waited = true;
-            try {
-              this.tablesBeingLocated.wait(threadWakeFrequency);
-            } catch (InterruptedException e) {
-              // continue
-            }
-          }
-          if (!waited) {
-            this.tablesBeingLocated.add(tableName);
-            
-          } else {
-            SortedMap<Text, HRegionLocation> tableServers =
-              this.tablesToServers.get(tableName);
-            
-            if (tableServers == null) {
-              throw new TableNotFoundException("table not found: " + tableName);
-            }
-            srvrs.putAll(tableServers);
-          }
-        }
-        if (!waited) {
-          try {
-            SortedMap<Text, HRegionLocation> metaServers =
-              this.tablesToServers.get(META_TABLE_NAME);
-
-            for (boolean refindMeta = true; refindMeta; ) {
-              if (metaServers == null || metaServers.size() == 0) {
-                // (re)find the meta table
-                metaServers = findServersForTable(META_TABLE_NAME);
-                // but don't try again
-                refindMeta = false;
-              }
-              try {
-                srvrs = getTableServers(metaServers, tableName);
-                break;
-
-              } catch (NotServingRegionException e) {
-                if (!refindMeta) {
-                  // Already refound meta once. Give up.
-                  throw e;
-                }
-                // The meta table must have moved - refind it
-                metaServers.clear();
-              }
-            }
-            this.tablesToServers.put(tableName, srvrs);
-          } finally {
-            synchronized (this.tablesBeingLocated) {
-              // Wake up the threads waiting for us to find the table
-              this.tablesBeingLocated.remove(tableName);
-              this.tablesBeingLocated.notifyAll();
-            }
-          }
-        }
-      }
-      this.tablesToServers.put(tableName, srvrs);
-      return srvrs;
-    }
-
     /*
      * Repeatedly try to find the root region by asking the master for where it is
-     * @return TreeMap<Text, TableInfo> for root regin if found
+     * @return HRegionLocation for root region if found
      * @throws NoServerForRegionException - if the root region can not be located
      * after retrying
      * @throws IOException 
      */
-    private TreeMap<Text, HRegionLocation> locateRootRegion()
+    private HRegionLocation locateRootRegion()
     throws IOException {
     
       getMaster();
       
-      HServerAddress rootRegionLocation = null;
+      HServerAddress rootRegionAddress = null;
+      
       for (int tries = 0; tries < numRetries; tries++) {
         int localTimeouts = 0;
-        while (rootRegionLocation == null && localTimeouts < numRetries) {
+        
-          rootRegionLocation = master.findRootRegion();
+        // ask the master which server has the root region
-          if (rootRegionLocation == null) {
+        while (rootRegionAddress == null && localTimeouts < numRetries) {
+          rootRegionAddress = master.findRootRegion();
+          if (rootRegionAddress == null) {
             try {
               if (LOG.isDebugEnabled()) {
                 LOG.debug("Sleeping. Waiting for root region.");
@@ -591,15 +714,18 @@ public class HConnectionManager implements HConstants {
           }
         }
         
-        if (rootRegionLocation == null) {
+        if (rootRegionAddress == null) {
           throw new NoServerForRegionException(
               "Timed out trying to locate root region");
         }
         
-        HRegionInterface rootRegion = getHRegionConnection(rootRegionLocation);
+        // get a connection to the region server
+        HRegionInterface server = getHRegionConnection(rootRegionAddress);
 
         try {
-          rootRegion.getRegionInfo(HRegionInfo.rootRegionInfo.getRegionName());
+          // if this works, then we're good, and we have an acceptable address,
+          // so we can stop doing retries and return the result.
+          server.getRegionInfo(HRegionInfo.rootRegionInfo.getRegionName());
           break;
         } catch (IOException e) {
           if (tries == numRetries - 1) {
@@ -624,183 +750,20 @@ public class HConnectionManager implements HConstants {
             // continue
           }
         }
-        rootRegionLocation = null;
+        
+        rootRegionAddress = null;
       }
       
-      if (rootRegionLocation == null) {
+      // if the adress is null by this point, then the retries have failed,
+      // and we're sort of sunk
+      if (rootRegionAddress == null) {
         throw new NoServerForRegionException(
           "unable to locate root region server");
       }
       
-      TreeMap<Text, HRegionLocation> rootServer =
+      // return the region location
-        new TreeMap<Text, HRegionLocation>();
+      return new HRegionLocation(
-      
+        HRegionInfo.rootRegionInfo, rootRegionAddress);
-      rootServer.put(EMPTY_START_ROW,
-          new HRegionLocation(HRegionInfo.rootRegionInfo, rootRegionLocation));
-      
-      return rootServer;
-    }
-    
-    /*
-     * @param metaServers the meta servers that would know where the table is
-     * @param tableName name of the table
-     * @return map of region start key -> server location
-     * @throws IOException
-     */
-    private SortedMap<Text, HRegionLocation> getTableServers(
-        final SortedMap<Text, HRegionLocation> metaServers,
-        final Text tableName) throws IOException {
-
-      // If there is more than one meta server, find the first one that should
-      // know about the table we are looking for, and reduce the number of
-      // servers we need to query.
-      
-      SortedMap<Text, HRegionLocation> metaServersForTable = metaServers;
-      if (metaServersForTable.size() > 1) {
-        Text firstMetaRegion = metaServersForTable.headMap(tableName).lastKey();
-        metaServersForTable = metaServersForTable.tailMap(firstMetaRegion);
-      }
-      
-      SortedMap<Text, HRegionLocation> tableServers =
-        new TreeMap<Text, HRegionLocation>();
-      
-      int tries = 0;
-      do {
-        if (tries >= numRetries - 1) {
-          throw new NoServerForRegionException(
-              "failed to find server for " + tableName + " after "
-              + numRetries + " retries");
-
-        } else if (tries > 0) {
-          if (LOG.isDebugEnabled()) {
-            LOG.debug("Sleeping. Table " + tableName +
-            " not currently being served.");
-          }
-          try {
-            Thread.sleep(pause);
-          } catch (InterruptedException ie) {
-            // continue
-          }
-          if (LOG.isDebugEnabled()) {
-            LOG.debug("Wake. Retry finding table " + tableName);
-          }
-        }
-        for (HRegionLocation t: metaServersForTable.values()) {
-          tableServers.putAll(scanOneMetaRegion(t, tableName));
-        }
-        tries += 1;
-      } while (tableServers.size() == 0);
-      return tableServers;
-    }
-
-    /*
-     * Scans a single meta region
-     * @param t the meta region we're going to scan
-     * @param tableName the name of the table we're looking for
-     * @return returns a map of startingRow to TableInfo
-     * @throws TableNotFoundException - if table does not exist
-     * @throws IllegalStateException - if table is offline
-     * @throws IOException 
-     */
-    private SortedMap<Text, HRegionLocation> scanOneMetaRegion(
-        final HRegionLocation t, final Text tableName) throws IOException {
-      
-      HRegionInterface server = getHRegionConnection(t.getServerAddress());
-      TreeMap<Text, HRegionLocation> servers =
-        new TreeMap<Text, HRegionLocation>();
-      
-      long scannerId = -1L;
-      try {
-        scannerId = server.openScanner(t.getRegionInfo().getRegionName(),
-            COLUMN_FAMILY_ARRAY, tableName, System.currentTimeMillis(), null);
-
-        while (true) {
-          HbaseMapWritable values = server.next(scannerId);
-          if (values == null || values.size() == 0) {
-            if (servers.size() == 0) {
-              // If we didn't find any servers then the table does not exist
-              throw new TableNotFoundException("table '" + tableName +
-                  "' does not exist in " + t);
-            }
-
-            // We found at least one server for the table and now we're done.
-            if (LOG.isDebugEnabled()) {
-              LOG.debug("Found " + servers.size() + " region(s) for " +
-                  tableName + " at " + t);
-            }
-            break;
-          }
-
-          SortedMap<Text, byte[]> results = new TreeMap<Text, byte[]>();
-          for (Map.Entry<Writable, Writable> e: values.entrySet()) {
-            HStoreKey key = (HStoreKey) e.getKey();
-            results.put(key.getColumn(),
-                ((ImmutableBytesWritable) e.getValue()).get());
-          }
-
-          byte[] bytes = results.get(COL_REGIONINFO);
-          if (bytes == null || bytes.length == 0) {
-            // This can be null.  Looks like an info:splitA or info:splitB
-            // is only item in the row.
-            if (LOG.isDebugEnabled()) {
-              LOG.debug(COL_REGIONINFO.toString() + " came back empty: " +
-                  results.toString());
-            }
-            servers.clear();
-            break;
-          }
-
-          HRegionInfo regionInfo = (HRegionInfo) Writables.getWritable(
-              results.get(COL_REGIONINFO), new HRegionInfo());
-
-          if (!regionInfo.getTableDesc().getName().equals(tableName)) {
-            // We're done
-            if (LOG.isDebugEnabled()) {
-              LOG.debug("Found " + servers.size() + " servers for table " +
-                  tableName);
-            }
-            break;
-          }
-
-          if (regionInfo.isSplit()) {
-            // Region is a split parent. Skip it.
-            continue;
-          }
-
-          if (regionInfo.isOffline()) {
-            throw new IllegalStateException("table offline: " + tableName);
-          }
-
-          bytes = results.get(COL_SERVER);
-          if (bytes == null || bytes.length == 0) {
-            // We need to rescan because the table we want is unassigned.
-            if (LOG.isDebugEnabled()) {
-              LOG.debug("no server address for " + regionInfo.toString());
-            }
-            servers.clear();
-            break;
-          }
-
-          String serverAddress = Writables.bytesToString(bytes);
-          servers.put(regionInfo.getStartKey(), new HRegionLocation(
-              regionInfo, new HServerAddress(serverAddress)));
-        }
-      } catch (IOException e) {
-        if (e instanceof RemoteException) {
-          e = RemoteExceptionHandler.decodeRemoteException((RemoteException) e);
-        }
-        throw e;
-
-      } finally {
-        if (scannerId != -1L) {
-          try {
-            server.close(scannerId);
-          } catch (Exception ex) {
-            LOG.warn(ex);
-          }
-        }
-      }
-      return servers;
     }
   }
 }

src/java/org/apache/hadoop/hbase/HRegion.java

@@ -551,6 +551,7 @@ public class HRegion implements HConstants {
       if (closed.get() || !needsSplit(midKey)) {
         return null;
       }
+
       long startTime = System.currentTimeMillis();
       Path splits = new Path(this.regiondir, SPLITDIR);
       if(!this.fs.exists(splits)) {
@@ -1036,6 +1037,57 @@ public class HRegion implements HConstants {
     }
   }
 
+  /**
+   * Return all the data for the row that matches <i>row</i> exactly, 
+   * or the one that immediately preceeds it, at or immediately before 
+   * <i>ts</i>.
+   * 
+   * @param row row key
+   * @return map of values
+   * @throws IOException
+   */
+  public Map<Text, byte[]> getClosestRowBefore(final Text row, final long ts)
+  throws IOException{
+    // look across all the HStores for this region and determine what the
+    // closest key is across all column families, since the data may be sparse
+    
+    HStoreKey key = null;
+    checkRow(row);
+    lock.readLock().lock();
+    try {
+      // examine each column family for the preceeding or matching key
+      for(Text colFamily : stores.keySet()){
+        HStore store = stores.get(colFamily);
+
+        // get the closest key
+        Text closestKey = store.getRowKeyAtOrBefore(row, ts);
+        
+        // if it happens to be an exact match, we can stop looping
+        if (row.equals(closestKey)) {
+          key = new HStoreKey(closestKey, ts);
+          break;
+        }
+
+        // otherwise, we need to check if it's the max and move to the next
+        if (closestKey != null 
+          && (key == null || closestKey.compareTo(key.getRow()) > 0) ) {
+          key = new HStoreKey(closestKey, ts);
+        }
+      }
+          
+      // now that we've found our key, get the values
+      TreeMap<Text, byte []> result = new TreeMap<Text, byte[]>();
+      for (Text colFamily: stores.keySet()) {
+        HStore targetStore = stores.get(colFamily);
+        targetStore.getFull(key, result);
+      }
+      
+      return result;
+    } finally {
+      lock.readLock().unlock();
+    }
+  }
+
   /**
    * Get <code>versions</code> keys matching the origin key's
    * row/column/timestamp and those of an older vintage

src/java/org/apache/hadoop/hbase/HRegionInfo.java

@@ -251,7 +251,8 @@ public class HRegionInfo implements WritableComparable {
   @Override
   public String toString() {
     return "regionname: " + this.regionName.toString() + ", startKey: <" +
-      this.startKey.toString() + ">, encodedName(" + getEncodedName() + ")" +
+      this.startKey.toString() + ">, endKey: <" + this.endKey.toString() + 
+      ">, encodedName(" + getEncodedName() + ")" +
       (isOffline()? " offline: true,": "") + (isSplit()? " split: true,": "") +
       " tableDesc: {" + this.tableDesc.toString() + "}";
   }

src/java/org/apache/hadoop/hbase/HRegionInterface.java

@@ -110,6 +110,31 @@ public interface HRegionInterface extends VersionedProtocol {
   public HbaseMapWritable getRow(final Text regionName, final Text row, final long ts)
   throws IOException;
 
+  /**
+   * Return all the data for the row that matches <i>row</i> exactly, 
+   * or the one that immediately preceeds it.
+   * 
+   * @param regionName region name
+   * @param row row key
+   * @return map of values
+   * @throws IOException
+   */
+  public HbaseMapWritable getClosestRowBefore(final Text regionName, final Text row)
+  throws IOException;
+
+  /**
+   * Return all the data for the row that matches <i>row</i> exactly, 
+   * or the one that immediately preceeds it, at or immediately before 
+   * <i>ts</i>.
+   * 
+   * @param regionName region name
+   * @param row row key
+   * @return map of values
+   * @throws IOException
+   */
+  public HbaseMapWritable getClosestRowBefore(final Text regionName, 
+    final Text row, final long ts)
+  throws IOException;
 
   /**
    * Applies a batch of updates via one RPC

src/java/org/apache/hadoop/hbase/HRegionServer.java

@@ -1409,6 +1409,38 @@ public class HRegionServer implements HConstants, HRegionInterface, Runnable {
     }
   }
 
+  /** {@inheritDoc} */
+  public HbaseMapWritable getClosestRowBefore(final Text regionName, 
+    final Text row)
+  throws IOException {
+    return getClosestRowBefore(regionName, row, HConstants.LATEST_TIMESTAMP);
+  }
+
+  /** {@inheritDoc} */
+  public HbaseMapWritable getClosestRowBefore(final Text regionName, 
+    final Text row, final long ts)
+  throws IOException {
+
+    checkOpen();
+    requestCount.incrementAndGet();
+    try {
+      // locate the region we're operating on
+      HRegion region = getRegion(regionName);
+      HbaseMapWritable result = new HbaseMapWritable();
+      // ask the region for all the data 
+      Map<Text, byte[]> map = region.getClosestRowBefore(row, ts);
+      // convert to a MapWritable
+      for (Map.Entry<Text, byte []> es: map.entrySet()) {
+        result.put(new HStoreKey(row, es.getKey()),
+            new ImmutableBytesWritable(es.getValue()));
+      }
+      return result;
+      
+    } catch (IOException e) {
+      checkFileSystem();
+      throw e;
+    }
+  }
 
   /** {@inheritDoc} */
   public HbaseMapWritable next(final long scannerId) throws IOException {
@@ -1428,6 +1460,7 @@ public class HRegionServer implements HConstants, HRegionInterface, Runnable {
       HStoreKey key = new HStoreKey();
       TreeMap<Text, byte []> results = new TreeMap<Text, byte []>();
       while (s.next(key, results)) {
+/*        LOG.debug("RegionServer scanning on row " + key.getRow());*/
         for(Map.Entry<Text, byte []> e: results.entrySet()) {
           values.put(new HStoreKey(key.getRow(), e.getKey(), key.getTimestamp()),
             new ImmutableBytesWritable(e.getValue()));

src/java/org/apache/hadoop/hbase/HStore.java

@@ -191,6 +191,10 @@ public class HStore implements HConstants {
     private void internalGetFull(SortedMap<HStoreKey, byte []> map, HStoreKey key, 
         SortedMap<Text, byte []> results) {
 
+      if (map.isEmpty()) {
+        return;
+      }
+
       SortedMap<HStoreKey, byte []> tailMap = map.tailMap(key);
       for (Map.Entry<HStoreKey, byte []> es: tailMap.entrySet()) {
         HStoreKey itKey = es.getKey();
@@ -208,6 +212,96 @@ public class HStore implements HConstants {
       }
     }
 
+    /**
+     * Find the key that matches <i>row</i> exactly, or the one that immediately
+     * preceeds it.
+     */
+    public Text getRowKeyAtOrBefore(final Text row, long timestamp)
+    throws IOException{
+      this.lock.readLock().lock();
+      
+      Text key_memcache = null;
+      Text key_snapshot = null;
+      
+      try {
+        synchronized (memcache) {
+          key_memcache = internalGetRowKeyAtOrBefore(memcache, row, timestamp);
+        }
+        synchronized (snapshot) {
+          key_snapshot = internalGetRowKeyAtOrBefore(snapshot, row, timestamp);
+        }
+
+        if (key_memcache == null && key_snapshot == null) {
+          // didn't find any candidates, return null
+          return null;
+        } else if (key_memcache == null && key_snapshot != null) {
+          return key_snapshot;
+        } else if (key_memcache != null && key_snapshot == null) {
+          return key_memcache;
+        } else {
+          // if either is a precise match, return the original row.
+          if ( (key_memcache != null && key_memcache.equals(row)) 
+            || (key_snapshot != null && key_snapshot.equals(row)) ) {
+            return row;
+          } else {
+            // no precise matches, so return the one that is closer to the search
+            // key (greatest)
+            return key_memcache.compareTo(key_snapshot) > 0 ? 
+              key_memcache : key_snapshot;
+          }          
+        }
+      } finally {
+        this.lock.readLock().unlock();
+      }
+    }
+
+    private Text internalGetRowKeyAtOrBefore(SortedMap<HStoreKey, byte []> map, 
+      Text key, long timestamp) {
+      // TODO: account for deleted cells
+
+      HStoreKey search_key = new HStoreKey(key, timestamp);
+
+      // get all the entries that come equal or after our search key
+      SortedMap<HStoreKey, byte []> tailMap = map.tailMap(search_key);
+
+      // if the first item in the tail has a matching row, then we have an 
+      // exact match, and we should return that item
+      if (!tailMap.isEmpty() && tailMap.firstKey().getRow().equals(key)) {
+        // seek forward past any cells that don't fulfill the timestamp
+        // argument
+        Iterator<HStoreKey> key_iterator = tailMap.keySet().iterator();
+        HStoreKey found_key = key_iterator.next();
+        
+        // keep seeking so long as we're in the same row, and the timstamp
+        // isn't as small as we'd like, and there are more cells to check
+        while (found_key.getRow().equals(key)
+          && found_key.getTimestamp() > timestamp && key_iterator.hasNext()) {
+          found_key = key_iterator.next();
+        }
+        
+        // if this check fails, then we've iterated through all the keys that 
+        // match by row, but none match by timestamp, so we fall through to
+        // the headMap case.
+        if (found_key.getTimestamp() <= timestamp) {
+          // we didn't find a key that matched by timestamp, so we have to 
+          // return null;
+/*          LOG.debug("Went searching for " + key + ", found " + found_key.getRow());*/
+          return found_key.getRow();
+        }
+      }
+      
+      // the tail didn't contain the key we're searching for, so we should
+      // use the last key in the headmap as the closest before
+      SortedMap<HStoreKey, byte []> headMap = map.headMap(search_key);
+      if (headMap.isEmpty()) {
+/*        LOG.debug("Went searching for " + key + ", found nothing!");*/
+        return null;
+      } else {
+/*        LOG.debug("Went searching for " + key + ", found " + headMap.lastKey().getRow());*/
+        return headMap.lastKey().getRow();
+      }
+    }
+    
     /**
      * Examine a single map for the desired key.
      *
@@ -1706,6 +1800,116 @@ public class HStore implements HConstants {
     }
   }
   
+  /**
+   * Find the key that matches <i>row</i> exactly, or the one that immediately
+   * preceeds it.
+   */
+  public Text getRowKeyAtOrBefore(final Text row, final long timestamp)
+  throws IOException{
+    // if the exact key is found, return that key
+    // if we find a key that is greater than our search key, then use the 
+    // last key we processed, and if that was null, return null.
+
+    Text foundKey = memcache.getRowKeyAtOrBefore(row, timestamp);
+    if (foundKey != null) {
+      return foundKey;
+    }
+    
+    // obtain read lock
+    this.lock.readLock().lock();
+    try {
+      MapFile.Reader[] maparray = getReaders();
+      
+      Text bestSoFar = null;
+      
+      HStoreKey rowKey = new HStoreKey(row, timestamp);
+      
+      // process each store file
+      for(int i = maparray.length - 1; i >= 0; i--) {
+        Text row_from_mapfile = 
+          rowAtOrBeforeFromMapFile(maparray[i], row, timestamp);
+
+        // for when we have MapFile.Reader#getClosest before functionality
+/*        Text row_from_mapfile = null;
+        WritableComparable value = null; 
+        
+        HStoreKey hskResult = 
+          (HStoreKey)maparray[i].getClosest(rowKey, value, true);
+        
+        if (hskResult != null) {
+          row_from_mapfile = hskResult.getRow();
+        }*/
+                
+/*        LOG.debug("Best from this mapfile was " + row_from_mapfile);*/
+        
+        // short circuit on an exact match
+        if (row.equals(row_from_mapfile)) {
+          return row;
+        }
+        
+        // check to see if we've found a new closest row key as a result
+        if (bestSoFar == null || bestSoFar.compareTo(row_from_mapfile) < 0) {
+          bestSoFar = row_from_mapfile;
+        }
+      }
+      
+/*      LOG.debug("Went searching for " + row + ", found " + bestSoFar);*/
+      return bestSoFar;
+    } finally {
+      this.lock.readLock().unlock();
+    }
+  }
+  
+  /**
+   * Check an individual MapFile for the row at or before a given key 
+   * and timestamp
+   */
+  private Text rowAtOrBeforeFromMapFile(MapFile.Reader map, Text row, 
+    long timestamp)
+  throws IOException {
+    Text previousRow = null;
+    ImmutableBytesWritable readval = new ImmutableBytesWritable();
+    HStoreKey readkey = new HStoreKey();
+    
+    synchronized(map) {
+      // start at the beginning of the map
+      // TODO: this sucks. do a clever binary search instead.
+      map.reset();
+    
+      while(map.next(readkey, readval)){
+        if (readkey.getRow().compareTo(row) == 0) {
+          // exact match on row
+          if (readkey.getTimestamp() <= timestamp) {
+            // timestamp fits, return this key
+            return readkey.getRow();
+          }
+          
+          // getting here means that we matched the row, but the timestamp
+          // is too recent - hopefully one of the next cells will match
+          // better, so keep rolling
+        }        
+        // if the row key we just read is beyond the key we're searching for,
+        // then we're done; return the last key we saw before this one
+        else if (readkey.getRow().toString().compareTo(row.toString()) > 0 ) {
+          return previousRow;
+        } else {
+          // so, the row key doesn't match, and we haven't gone past the row
+          // we're seeking yet, so this row is a candidate for closest, as
+          // long as the timestamp is correct.
+          if (readkey.getTimestamp() <= timestamp) {
+            previousRow = new Text(readkey.getRow());
+          }
+          // otherwise, ignore this key, because it doesn't fulfill our 
+          // requirements.
+        }
+      }
+    }
+    // getting here means we exhausted all of the cells in the mapfile.
+    // whatever satisfying row we reached previously is the row we should 
+    // return
+    return previousRow;
+  }
+  
   /**
    * Test that the <i>target</i> matches the <i>origin</i>. If the 
    * <i>origin</i> has an empty column, then it's assumed to mean any column 

src/java/org/apache/hadoop/hbase/HTable.java

@@ -20,6 +20,7 @@
 package org.apache.hadoop.hbase;
 
 import java.io.IOException;
+import java.util.List;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Iterator;
@@ -55,7 +56,6 @@ public class HTable implements HConstants {
   protected final long pause;
   protected final int numRetries;
   protected Random rand;
-  protected volatile SortedMap<Text, HRegionLocation> tableServers;
   protected AtomicReference<BatchUpdate> batch;
 
   protected volatile boolean tableDoesNotExist;
@@ -89,7 +89,6 @@ public class HTable implements HConstants {
     this.numRetries = conf.getInt("hbase.client.retries.number", 5);
     this.rand = new Random();
     this.batch = new AtomicReference<BatchUpdate>();
-    tableServers = connection.getTableServers(tableName);
     tableDoesNotExist = false;
     closed = false;
   }
@@ -99,18 +98,22 @@ public class HTable implements HConstants {
    * @param row Row to find.
    * @return Location of row.
    */
-  HRegionLocation getRegionLocation(Text row) {
+  HRegionLocation getRegionLocation(Text row) throws IOException {
     checkClosed();
-    if (this.tableServers == null) {
+    return this.connection.locateRegion(this.tableName, row);
-      throw new IllegalStateException("Must open table first");
-    }
-    
-    // Only one server will have the row we are looking for
-    Text serverKey = (this.tableServers.containsKey(row)) ?
-        row : this.tableServers.headMap(row).lastKey();
-    return this.tableServers.get(serverKey);
   }
 
+  /**
+   * Find region location hosting passed row using cached info
+   * @param row Row to find.
+   * @return Location of row.
+   */
+  HRegionLocation getRegionLocation(Text row, boolean reload) throws IOException {
+    checkClosed();
+    return this.connection.relocateRegion(this.tableName, row);
+  }
+
+
   /** @return the connection */
   public HConnection getConnection() {
     checkClosed();
@@ -124,7 +127,6 @@ public class HTable implements HConstants {
   public synchronized void close() {
     if (!closed) {
       closed = true;
-      tableServers = null;
       batch.set(null);
       connection.close(tableName);
     }
@@ -185,14 +187,78 @@ public class HTable implements HConstants {
    * Gets the starting row key for every region in the currently open table
    * @return Array of region starting row keys
    */
-  public Text[] getStartKeys() {
+  public Text[] getStartKeys() throws IOException {
     checkClosed();
-    Text[] keys = new Text[tableServers.size()];
+    List<Text> keyList = new ArrayList<Text>();
-    int i = 0;
+
-    for(Text key: tableServers.keySet()){
+    long scannerId = -1L;
-      keys[i++] = key;
+
+    Text startRow = new Text(tableName.toString() + ",,999999999999999");
+    HRegionLocation metaLocation = null;
+
+    // scan over the each meta region
+    do {
+      try{
+        // turn the start row into a location
+        metaLocation = 
+          connection.locateRegion(META_TABLE_NAME, startRow);
+
+        // connect to the server hosting the .META. region
+        HRegionInterface server = 
+          connection.getHRegionConnection(metaLocation.getServerAddress());
+
+        // open a scanner over the meta region
+        scannerId = server.openScanner(
+          metaLocation.getRegionInfo().getRegionName(),
+          COLUMN_FAMILY_ARRAY, EMPTY_START_ROW, LATEST_TIMESTAMP,
+          null);
+        
+        // iterate through the scanner, accumulating unique table names
+        SCANNER_LOOP: while (true) {
+          HbaseMapWritable values = server.next(scannerId);
+          if (values == null || values.size() == 0) {
+            break;
+          }
+          for (Map.Entry<Writable, Writable> e: values.entrySet()) {
+            HStoreKey key = (HStoreKey) e.getKey();
+            if (key.getColumn().equals(COL_REGIONINFO)) {
+              HRegionInfo info = new HRegionInfo();
+              info = (HRegionInfo) Writables.getWritable(
+                  ((ImmutableBytesWritable) e.getValue()).get(), info);
+
+              if (!info.getTableDesc().getName().equals(this.tableName)) {
+                break SCANNER_LOOP;
+              }
+
+              if (info.isOffline()) {
+                LOG.debug("Region " + info + " was offline!");
+                break;
+              }
+
+              if (info.isSplit()) {
+                LOG.debug("Region " + info + " was split!");
+                break;
+              }
+
+              keyList.add(info.getStartKey());
+            }
+          }
+        }
+          
+        // advance the startRow to the end key of the current region
+        startRow = metaLocation.getRegionInfo().getEndKey();          
+      } catch (IOException e) {
+        // need retry logic?
+        throw e;
+      }
+    } while (startRow.compareTo(EMPTY_START_ROW) != 0);
+
+    Text[] arr = new Text[keyList.size()];
+    for (int i = 0; i < keyList.size(); i++ ){
+      arr[i] = keyList.get(i);
     }
-    return keys;
+    
+    return arr;
   }
   
   /** 
@@ -225,7 +291,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -270,7 +336,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -326,7 +392,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -387,7 +453,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);        
       }
       try {
         Thread.sleep(this.pause);
@@ -728,7 +794,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -765,7 +831,8 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+/*        tableServers = connection.reloadTableServers(tableName);*/
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -814,7 +881,7 @@ public class HTable implements HConstants {
         if (LOG.isDebugEnabled()) {
           LOG.debug("reloading table servers because: " + e.getMessage());
         }
-        tableServers = connection.reloadTableServers(tableName);
+        r = getRegionLocation(row, true);
       }
       try {
         Thread.sleep(this.pause);
@@ -900,11 +967,11 @@ public class HTable implements HConstants {
             e = RemoteExceptionHandler.decodeRemoteException(
                 (RemoteException) e);
           }
-          if (tries < numRetries -1) {
+          if (tries < numRetries - 1) {
             if (LOG.isDebugEnabled()) {
               LOG.debug("reloading table servers because: " + e.getMessage());
             }
-            tableServers = connection.reloadTableServers(tableName);
+            r = getRegionLocation(batch.get().getRow(), true);
           } else {
             throw e;
           }
@@ -945,47 +1012,34 @@ public class HTable implements HConstants {
     private long scanTime;
     @SuppressWarnings("hiding")
     private boolean closed;
-    private AtomicReferenceArray<HRegionLocation> regions;
+    private HRegionLocation currentRegionLocation;
-    @SuppressWarnings("hiding")
-    private int currentRegion;
     private HRegionInterface server;
     private long scannerId;
     private RowFilterInterface filter;
     
-    private void loadRegions() {
-      checkClosed();
-      Text firstServer = null;
-      if (this.startRow == null || this.startRow.getLength() == 0) {
-        firstServer = tableServers.firstKey();
-
-      } else if(tableServers.containsKey(startRow)) {
-        firstServer = startRow;
-
-      } else {
-        firstServer = tableServers.headMap(startRow).lastKey();
-      }
-      Collection<HRegionLocation> info =
-        tableServers.tailMap(firstServer).values();
-      
-      this.regions = new AtomicReferenceArray<HRegionLocation>(
-          info.toArray(new HRegionLocation[info.size()]));
-    }
-    
     protected ClientScanner(Text[] columns, Text startRow, long timestamp,
-        RowFilterInterface filter) throws IOException {
+      RowFilterInterface filter) 
+    throws IOException {
 
+      LOG.info("Creating scanner over " + tableName + " starting at key " + startRow);
+
+      // defaults
+      this.closed = false;
+      this.server = null;
+      this.scannerId = -1L;
+    
+      // save off the simple parameters
       this.columns = columns;
       this.startRow = startRow;
       this.scanTime = timestamp;
-      this.closed = false;
+      
+      // save the filter, and make sure that the filter applies to the data
+      // we're expecting to pull back
       this.filter = filter;
       if (filter != null) {
         filter.validate(columns);
       }
-      loadRegions();
+
-      this.currentRegion = -1;
-      this.server = null;
-      this.scannerId = -1L;
       nextScanner();
     }
         
@@ -995,37 +1049,52 @@ public class HTable implements HConstants {
      */
     private boolean nextScanner() throws IOException {
       checkClosed();
+      
+      // close the previous scanner if it's open
       if (this.scannerId != -1L) {
         this.server.close(this.scannerId);
         this.scannerId = -1L;
       }
-      this.currentRegion += 1;
+
-      if (this.currentRegion == this.regions.length()) {
+      // if we're at the end of the table, then close and return false
-        close();
+      // to stop iterating
-        return false;
+      if (this.currentRegionLocation != null){
+        LOG.debug("Advancing forward from region " 
+          + this.currentRegionLocation.getRegionInfo());
+        
+        if (this.currentRegionLocation.getRegionInfo().getEndKey() == null
+          || this.currentRegionLocation.getRegionInfo().getEndKey().equals(EMPTY_TEXT)) {
+            LOG.debug("We're at the end of the region, returning.");
+            close();
+            return false;
+        }
       } 
+      
+      HRegionLocation oldLocation = this.currentRegionLocation;
+      
+      Text localStartKey = oldLocation == null ? 
+        startRow : oldLocation.getRegionInfo().getEndKey();
+
+      // advance to the region that starts with the current region's end key
+      LOG.debug("Advancing internal scanner to startKey " + localStartKey);
+      this.currentRegionLocation = getRegionLocation(localStartKey);
+      
+      LOG.debug("New region: " + this.currentRegionLocation);
+      
       try {
         for (int tries = 0; tries < numRetries; tries++) {
-          HRegionLocation r = this.regions.get(currentRegion);
+          // connect to the server
-          this.server =
+          server = connection.getHRegionConnection(
-            connection.getHRegionConnection(r.getServerAddress());
+            this.currentRegionLocation.getServerAddress());
           
           try {
-            if (this.filter == null) {
+            // open a scanner on the region server starting at the 
-              this.scannerId =
+            // beginning of the region
-                this.server.openScanner(r.getRegionInfo().getRegionName(),
+            scannerId = server.openScanner(
-                    this.columns, currentRegion == 0 ? this.startRow
+              this.currentRegionLocation.getRegionInfo().getRegionName(),
-                        : EMPTY_START_ROW, scanTime, null);
+              this.columns, localStartKey, scanTime, filter);
-              
-            } else {
-              this.scannerId =
-                this.server.openScanner(r.getRegionInfo().getRegionName(),
-                    this.columns, currentRegion == 0 ? this.startRow
-                        : EMPTY_START_ROW, scanTime, filter);
-            }
               
             break;
-        
           } catch (IOException e) {
             if (e instanceof RemoteException) {
               e = RemoteExceptionHandler.decodeRemoteException(
@@ -1038,8 +1107,7 @@ public class HTable implements HConstants {
             if (LOG.isDebugEnabled()) {
               LOG.debug("reloading table servers because: " + e.getMessage());
             }
-            tableServers = connection.reloadTableServers(tableName);
+            currentRegionLocation = getRegionLocation(localStartKey, true);
-            loadRegions();
           }
         }
         try {
@@ -1068,7 +1136,7 @@ public class HTable implements HConstants {
       // calls to next.
       results.clear();
       do {
-        values = this.server.next(this.scannerId);
+        values = server.next(scannerId);
       } while (values != null && values.size() == 0 && nextScanner());
 
       if (values != null && values.size() != 0) {
@@ -1089,9 +1157,9 @@ public class HTable implements HConstants {
      */
     public void close() throws IOException {
       checkClosed();
-      if (this.scannerId != -1L) {
+      if (scannerId != -1L) {
         try {
-          this.server.close(this.scannerId);
+          server.close(scannerId);
           
         } catch (IOException e) {
           if (e instanceof RemoteException) {
@@ -1101,10 +1169,10 @@ public class HTable implements HConstants {
             throw e;
           }
         }
-        this.scannerId = -1L;
+        scannerId = -1L;
       }
-      this.server = null;
+      server = null;
-      this.closed = true;
+      closed = true;
     }
 
     /** {@inheritDoc} */

src/test/org/apache/hadoop/hbase/MultiRegionTable.java

@@ -136,39 +136,47 @@ public class MultiRegionTable extends HBaseTestCase {
     Path parentDir = HRegion.getRegionDir(new Path(d, tableName),
         parent.getEncodedName());
     assertTrue(fs.exists(parentDir));
-    LOG.info("Split happened. Parent is " + parent.getRegionName() +
+
-        " and daughters are " +
+    LOG.info("Split happened. Parent is " + parent.getRegionName());
-        ((splitA != null)? splitA.getRegionName(): "-") + ", " +
-        ((splitB != null)? splitB.getRegionName(): "-"));
 
     // Recalibrate will cause us to wait on new regions' deployment
     recalibrate(t, new Text(columnName), retries, waitTime);
 
-    // Compact a region at a time so we can test case where one region has
+    if (splitA == null) {
-    // no references but the other still has some
+      LOG.info("splitA was already null. Assuming it was previously compacted.");
-    compact(cluster, splitA);
+    } else {
+      LOG.info("Daughter splitA: " + splitA.getRegionName());
+      // Compact a region at a time so we can test case where one region has
+      // no references but the other still has some
+      compact(cluster, splitA);
       
-    // Wait till the parent only has reference to remaining split, one that
+      // Wait till the parent only has reference to remaining split, one that
-    // still has references.
+      // still has references.
-    while (true) {
+      while (true) {
-      data = getSplitParentInfo(meta, parent);
+        data = getSplitParentInfo(meta, parent);
-      if (data == null || data.size() == 3) {
+        if (data == null || data.size() == 3) {
-        try {
+          try {
-          Thread.sleep(waitTime);
+            Thread.sleep(waitTime);
-        } catch (InterruptedException e) {
+          } catch (InterruptedException e) {
-          // continue
+            // continue
+          }
+          continue;
         }
-        continue;
+        break;
       }
-      break;
+      LOG.info("Parent split info returned " + data.keySet().toString());
     }
-    LOG.info("Parent split info returned " + data.keySet().toString());
 
-    // Call second split.
+    if (splitB == null) {
-    compact(cluster, splitB);
+      LOG.info("splitB was already null. Assuming it was previously compacted.");
+    } else {
+      LOG.info("Daughter splitB: " + splitA.getRegionName());
+
+      // Call second split.
+      compact(cluster, splitB);
+    }
   
     // Now wait until parent disappears.    
-    
     LOG.info("Waiting on parent " + parent.getRegionName() + " to disappear");
     for (int i = 0; i < retries; i++) {
       if (getSplitParentInfo(meta, parent) == null) {

src/test/org/apache/hadoop/hbase/TestGet2.java

@@ -140,6 +140,82 @@ public class TestGet2 extends HBaseTestCase {
     }
   }
   
+  /** For HADOOP-2443 */
+  public void testGetClosestRowBefore() throws IOException{
+
+    HRegion region = null;
+    HRegionIncommon region_incommon = null;
+
+    try {
+      HTableDescriptor htd = createTableDescriptor(getName());
+      HRegionInfo hri = new HRegionInfo(htd, null, null);
+      region = createNewHRegion(htd, null, null);
+      region_incommon = new HRegionIncommon(region);
+     
+      // set up some test data
+      Text t10 = new Text("010");
+      Text t20 = new Text("020");
+      Text t30 = new Text("030");
+      Text t40 = new Text("040");
+      
+      long lockid = region_incommon.startBatchUpdate(t10);
+      region_incommon.put(lockid, COLUMNS[0], "t10 bytes".getBytes());
+      region_incommon.commit(lockid);
+      
+      lockid = region_incommon.startBatchUpdate(t20);
+      region_incommon.put(lockid, COLUMNS[0], "t20 bytes".getBytes());
+      region_incommon.commit(lockid);
+      
+      lockid = region_incommon.startBatchUpdate(t30);
+      region_incommon.put(lockid, COLUMNS[0], "t30 bytes".getBytes());
+      region_incommon.commit(lockid);
+      
+      lockid = region_incommon.startBatchUpdate(t40);
+      region_incommon.put(lockid, COLUMNS[0], "t40 bytes".getBytes());
+      region_incommon.commit(lockid);
+      
+      // try finding "015"
+      Text t15 = new Text("015");
+      Map<Text, byte[]> results = 
+        region.getClosestRowBefore(t15, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t10 bytes");
+
+      // try "020", we should get that row exactly
+      results = region.getClosestRowBefore(t20, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t20 bytes");
+
+      // try "050", should get stuff from "040"
+      Text t50 = new Text("050");
+      results = region.getClosestRowBefore(t50, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t40 bytes");
+
+      // force a flush
+      region.flushcache();
+
+      // try finding "015"      
+      results = region.getClosestRowBefore(t15, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t10 bytes");
+
+      // try "020", we should get that row exactly
+      results = region.getClosestRowBefore(t20, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t20 bytes");
+
+      // try "050", should get stuff from "040"
+      t50 = new Text("050");
+      results = region.getClosestRowBefore(t50, HConstants.LATEST_TIMESTAMP);
+      assertEquals(new String(results.get(COLUMNS[0])), "t40 bytes");
+    } finally {
+      if (region != null) {
+        try {
+          region.close();
+        } catch (Exception e) {
+          e.printStackTrace();
+        }
+        region.getLog().closeAndDelete();
+      }
+    }
+  }
+  
   
   private void assertCellValueEquals(final HRegion region, final Text row,
     final Text column, final long timestamp, final String value)

src/test/org/apache/hadoop/hbase/TestToString.java

@@ -55,7 +55,7 @@ public class TestToString extends TestCase {
     HRegionInfo hri = HRegionInfo.rootRegionInfo;
     System.out.println(hri.toString());
     assertEquals("HRegionInfo", 
-      "regionname: -ROOT-,,0, startKey: <>, encodedName(70236052) tableDesc: " +
+      "regionname: -ROOT-,,0, startKey: <>, endKey: <>, encodedName(70236052) tableDesc: " +
       "{name: -ROOT-, families: {info:={name: info, max versions: 1, " +
       "compression: NONE, in memory: false, max length: 2147483647, bloom " +
       "filter: none}}}", hri.toString());

src/test/org/apache/hadoop/hbase/mapred/TestTableIndex.java

@@ -126,6 +126,7 @@ public class TestTableIndex extends MultiRegionTable {
       StaticTestEnvironment.shutdownDfs(dfsCluster);
       throw e;
     }
+    LOG.debug("\n\n\n\n\t\t\tSetup Complete\n\n\n\n");
   }
 
   /** {@inheritDoc} */
@@ -252,7 +253,7 @@ public class TestTableIndex extends MultiRegionTable {
     // its snapshot, all the updates have made it into the cache.
     try {
       Thread.sleep(conf.getLong("hbase.regionserver.optionalcacheflushinterval",
-          60L * 1000L));
+        60L * 1000L));
     } catch (InterruptedException e) {
       // ignore
     }
@@ -295,13 +296,16 @@ public class TestTableIndex extends MultiRegionTable {
       int count = 0;
       while (scanner.next(key, results)) {
         String value = key.getRow().toString();
+        LOG.debug("Scanned over " + key.getRow());
         Term term = new Term(rowkeyName, value);
         int hitCount = searcher.search(new TermQuery(term)).length();
         assertEquals("check row " + value, 1, hitCount);
         count++;
       }
-      int maxDoc = searcher.maxDoc();
+      LOG.debug("Searcher.maxDoc: " + searcher.maxDoc());
-      assertEquals("check number of rows", count, maxDoc);
+      LOG.debug("IndexReader.numDocs: " + ((IndexSearcher)searcher).getIndexReader().numDocs());      
+      int maxDoc = ((IndexSearcher)searcher).getIndexReader().numDocs();
+      assertEquals("check number of rows", maxDoc, count);
     } finally {
       if (null != searcher)
         searcher.close();