HBASE-626 Use Visitor pattern in MetaRegion to reduce code clones in HTable and HConnectionManager

git-svn-id: https://svn.apache.org/repos/asf/hadoop/hbase/trunk@658337 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -36,6 +36,8 @@ Hbase Change Log
    HBASE-522   Where new Text(string) might be used in client side method calls,
                add an overload that takes string (Done as part of HBASE-82)
    HBASE-570   Remove HQL unit test (Done as part of HBASE-82 commit).
+   HBASE-626   Use Visitor pattern in MetaRegion to reduce code clones in HTable
+               and HConnectionManager (Jean-Daniel Cryans via Stack)
 
 
 Release 0.1.2 - 05/13/2008

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

@@ -42,6 +42,7 @@ import org.apache.hadoop.hbase.MasterNotRunningException;
 import org.apache.hadoop.hbase.NoServerForRegionException;
 import org.apache.hadoop.hbase.RemoteExceptionHandler;
 import org.apache.hadoop.hbase.TableNotFoundException;
+import org.apache.hadoop.hbase.client.MetaScanner.MetaScannerVisitor;
 import org.apache.hadoop.hbase.io.Cell;
 import org.apache.hadoop.hbase.io.RowResult;
 import org.apache.hadoop.hbase.ipc.HMasterInterface;
@@ -162,11 +163,14 @@ public class HConnectionManager implements HConstants {
     public HMasterInterface getMaster() throws MasterNotRunningException {
       HServerAddress masterLocation = null;
       synchronized (this.masterLock) {
-        for (int tries = 0; !this.closed &&
+        for (int tries = 0;
-            !this.masterChecked && this.master == null && tries < numRetries;
+          !this.closed &&
+          !this.masterChecked && this.master == null &&
+          tries < numRetries;
         tries++) {
-          String m = this.conf.get(MASTER_ADDRESS, DEFAULT_MASTER_ADDRESS);
+          
-          masterLocation = new HServerAddress(m);
+          masterLocation = new HServerAddress(this.conf.get(MASTER_ADDRESS,
+            DEFAULT_MASTER_ADDRESS));
           try {
             HMasterInterface tryMaster = (HMasterInterface)HbaseRPC.getProxy(
                 HMasterInterface.class, HMasterInterface.versionID, 
@@ -197,8 +201,11 @@ public class HConnectionManager implements HConstants {
         this.masterChecked = true;
       }
       if (this.master == null) {
-        throw new MasterNotRunningException(masterLocation == null? "":
+        if (masterLocation == null) {
-          masterLocation.toString());
+          throw new MasterNotRunningException();
+        } else {
+          throw new MasterNotRunningException(masterLocation.toString());
+        }
       }
       return this.master;
     }
@@ -257,39 +264,22 @@ public class HConnectionManager implements HConstants {
 
     /** {@inheritDoc} */
     public HTableDescriptor[] listTables() throws IOException {
-      HashSet<HTableDescriptor> uniqueTables = new HashSet<HTableDescriptor>();
+      final HashSet<HTableDescriptor> uniqueTables = new HashSet<HTableDescriptor>();
-      byte [] startRow = EMPTY_START_ROW;
 
-      // scan over the each meta region
+      MetaScannerVisitor visitor = new MetaScannerVisitor() {
-      do {
-        ScannerCallable callable = new ScannerCallable(this, META_TABLE_NAME,
-            COL_REGIONINFO_ARRAY, startRow, LATEST_TIMESTAMP, null);
-        try {
-          // open scanner
-          getRegionServerWithRetries(callable);
-          // iterate through the scanner, accumulating unique table names
-          while (true) {
-            RowResult values = getRegionServerWithRetries(callable);
-            if (values == null || values.size() == 0) {
-              break;
-            }
 
-            HRegionInfo info = 
+        public boolean processRow(RowResult rowResult,
-              Writables.getHRegionInfo(values.get(COL_REGIONINFO));
+            HRegionLocation metaLocation, HRegionInfo info) throws IOException {
 
           // Only examine the rows where the startKey is zero length
           if (info.getStartKey().length == 0) {
             uniqueTables.add(info.getTableDesc());
           }
+          return true;
         }
-          // advance the startRow to the end key of the current region
+
-          startRow = callable.getHRegionInfo().getEndKey();
+      };
-        } finally {
+      MetaScanner.metaScan(conf, visitor);
-          // close scanner
-          callable.setClose();
-          getRegionServerWithRetries(callable);
-        }
-      } while (Bytes.compareTo(startRow, LAST_ROW) != 0);
 
       return uniqueTables.toArray(new HTableDescriptor[uniqueTables.size()]);
     }
@@ -321,6 +311,7 @@ public class HConnectionManager implements HConstants {
           // 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.
+          
           if (!useCache || rootRegionLocation == null) {
             return locateRootRegion();
           }
@@ -652,20 +643,21 @@ public class HConnectionManager implements HConstants {
      */
     private HRegionLocation locateRootRegion()
     throws IOException {
+    
       getMaster();
+      
       HServerAddress rootRegionAddress = null;
+      
       for (int tries = 0; tries < numRetries; tries++) {
         int localTimeouts = 0;
-        // Ask the master which server has the root region
+        
+        // ask the master which server has the root region
         while (rootRegionAddress == null && localTimeouts < numRetries) {
           rootRegionAddress = master.findRootRegion();
           if (rootRegionAddress == null) {
-            // Increment and then only sleep if retries left.
-            if (++localTimeouts < numRetries) {
             try {
               if (LOG.isDebugEnabled()) {
-                  LOG.debug("Sleeping " + pause + "ms. Waiting for root "
+                LOG.debug("Sleeping. Waiting for root region.");
-                      + "region. Attempt " + tries + " of " + numRetries);
               }
               Thread.sleep(pause);
               if (LOG.isDebugEnabled()) {
@@ -674,7 +666,7 @@ public class HConnectionManager implements HConstants {
             } catch (InterruptedException iex) {
               // continue
             }
-            }
+            localTimeouts++;
           }
         }
         

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

@@ -1,5 +1,5 @@
 /**
- * Copyright 2007 The Apache Software Foundation
+ * Copyright 2008 The Apache Software Foundation
  *
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
@@ -35,15 +35,14 @@ import org.apache.hadoop.hbase.HRegionInfo;
 import org.apache.hadoop.hbase.HRegionLocation;
 import org.apache.hadoop.hbase.HServerAddress;
 import org.apache.hadoop.hbase.HTableDescriptor;
+import org.apache.hadoop.hbase.client.MetaScanner.MetaScannerVisitor;
 import org.apache.hadoop.hbase.filter.RowFilterInterface;
 import org.apache.hadoop.hbase.filter.StopRowFilter;
 import org.apache.hadoop.hbase.filter.WhileMatchRowFilter;
 import org.apache.hadoop.hbase.io.BatchUpdate;
 import org.apache.hadoop.hbase.io.Cell;
 import org.apache.hadoop.hbase.io.RowResult;
-import org.apache.hadoop.hbase.ipc.HRegionInterface;
 import org.apache.hadoop.hbase.util.Bytes;
-import org.apache.hadoop.hbase.util.Writables;
 import org.apache.hadoop.io.Text;
 
 /**
@@ -57,6 +56,7 @@ public class HTable implements HConstants {
   protected final long pause;
   protected final int numRetries;
   protected Random rand;
+  protected HBaseConfiguration configuration;
 
   protected volatile boolean tableDoesNotExist;
   
@@ -96,6 +96,7 @@ public class HTable implements HConstants {
   public HTable(HBaseConfiguration conf, final byte [] tableName)
   throws IOException {
     this.connection = HConnectionManager.getConnection(conf);
+    this.configuration = conf;
     this.tableName = tableName;
     this.pause = conf.getLong("hbase.client.pause", 10 * 1000);
     this.numRetries = conf.getInt("hbase.client.retries.number", 5);
@@ -142,142 +143,61 @@ 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
    * @throws IOException
    */
   @SuppressWarnings("null")
   public byte[][] getStartKeys() throws IOException {
-    List<byte []> keyList = new ArrayList<byte []>();
+    final List<byte[]> keyList = new ArrayList<byte[]>();
 
-    long scannerId = -1L;
+    MetaScannerVisitor visitor = new MetaScannerVisitor() {
-    byte [] startRow =
+      public boolean processRow(RowResult rowResult,
-      HRegionInfo.createRegionName(this.tableName, null, NINES);
+          HRegionLocation metaLocation, HRegionInfo info)
-    HRegionLocation metaLocation = null;
+      throws IOException {
-    HRegionInterface server;
+        if (!(Bytes.equals(info.getTableDesc().getName(), tableName))) {
-    
+          return false;
-    // 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
-        server = 
-          connection.getHRegionConnection(metaLocation.getServerAddress());
-
-        // open a scanner over the meta region
-        scannerId = server.openScanner(
-          metaLocation.getRegionInfo().getRegionName(),
-          new byte[][]{COL_REGIONINFO}, tableName, LATEST_TIMESTAMP,
-          null);
-        
-        // iterate through the scanner, accumulating unique region names
-        while (true) {
-          RowResult values = server.next(scannerId);
-          if (values == null || values.size() == 0) {
-            break;
-          }
-          
-          HRegionInfo info = new HRegionInfo();
-          info = (HRegionInfo) Writables.getWritable(
-            values.get(COL_REGIONINFO).getValue(), info);
-          
-          if (!Bytes.equals(info.getTableDesc().getName(), this.tableName)) {
-            break;
-          }
-          
-          if (info.isOffline() || info.isSplit()) {
-            continue;
         }
+        if (!(info.isOffline() || info.isSplit())) {
           keyList.add(info.getStartKey());
         }
-        
+        return true;
-        // close that remote scanner
-        server.close(scannerId);
-          
-        // advance the startRow to the end key of the current region
-        startRow = metaLocation.getRegionInfo().getEndKey();
-      } catch (IOException e) {
-        // need retry logic?
-        throw e;
       }
-    } while (Bytes.compareTo(startRow, EMPTY_START_ROW) != 0);
 
+    };
+    MetaScanner.metaScan(configuration, visitor, this.tableName);
     return keyList.toArray(new byte[keyList.size()][]);
   }
 
   /**
    * Get all the regions and their address for this table
+   * 
    * @return A map of HRegionInfo with it's server address
    * @throws IOException
    */
   @SuppressWarnings("null")
   public Map<HRegionInfo, HServerAddress> getRegionsInfo() throws IOException {
-    // TODO This code is a near exact copy of getStartKeys. To be refactored HBASE-626
+    final HashMap<HRegionInfo, HServerAddress> regionMap =
-    HashMap<HRegionInfo, HServerAddress> regionMap = new HashMap<HRegionInfo, HServerAddress>();
+      new HashMap<HRegionInfo, HServerAddress>();
 
-    long scannerId = -1L;
+    MetaScannerVisitor visitor = new MetaScannerVisitor() {
-    byte [] startRow =
+      public boolean processRow(RowResult rowResult,
-      HRegionInfo.createRegionName(this.tableName, null, NINES);
+          HRegionLocation metaLocation, HRegionInfo info)
-    HRegionLocation metaLocation = null;
+      throws IOException {
-    HRegionInterface server;
+        if (!(Bytes.equals(info.getTableDesc().getName(), tableName))) {
-        
+          return false;
-    // 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
-        server = 
-          connection.getHRegionConnection(metaLocation.getServerAddress());
-
-        // open a scanner over the meta region
-        scannerId = server.openScanner(
-          metaLocation.getRegionInfo().getRegionName(),
-          new byte [][]{COL_REGIONINFO}, tableName, LATEST_TIMESTAMP,
-          null);
-        
-        // iterate through the scanner, accumulating regions and their regionserver
-        while (true) {
-          RowResult values = server.next(scannerId);
-          if (values == null || values.size() == 0) {
-            break;
-          }
-          
-          HRegionInfo info = new HRegionInfo();
-          info = (HRegionInfo) Writables.getWritable(
-            values.get(COL_REGIONINFO).getValue(), info);
-
-          if (!Bytes.equals(info.getTableDesc().getName(), this.tableName)) {
-            break;
-          }
-          
-          if (info.isOffline() || info.isSplit()) {
-            continue;
         }
+        if (!(info.isOffline() || info.isSplit())) {
           regionMap.put(info, metaLocation.getServerAddress());
         }
-        
+        return true;
-        // close that remote scanner
-        server.close(scannerId);
-          
-        // advance the startRow to the end key of the current region
-        startRow = metaLocation.getRegionInfo().getEndKey();
-
-        // turn the start row into a location
-        metaLocation = 
-          connection.locateRegion(META_TABLE_NAME, startRow);
-      } catch (IOException e) {
-        // need retry logic?
-        throw e;
       }
-    } while (Bytes.compareTo(startRow, EMPTY_START_ROW) != 0);
 
+    };
+    MetaScanner.metaScan(configuration, visitor, tableName);
     return regionMap;
   }
+  
   /**
    * Get a single value for the specified row and column
    * 

src/java/org/apache/hadoop/hbase/client/MetaScanner.java

@@ -0,0 +1,98 @@
+package org.apache.hadoop.hbase.client;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hbase.HBaseConfiguration;
+import org.apache.hadoop.hbase.HConstants;
+import org.apache.hadoop.hbase.HRegionInfo;
+import org.apache.hadoop.hbase.HRegionLocation;
+import org.apache.hadoop.hbase.io.RowResult;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.hbase.util.Writables;
+
+/**
+ * Scanner class that contains the <code>.META.</code> table scanning logic 
+ * and uses a Retryable scanner. Provided visitors will be called
+ * for each row.
+ */
+class MetaScanner implements HConstants {
+
+  /**
+   * Scans the meta table and calls a visitor on each RowResult and uses a empty
+   * start row value as table name.
+   * 
+   * @param configuration
+   * @param visitor A custom visitor
+   * @throws IOException
+   */
+  public static void metaScan(HBaseConfiguration configuration,
+      MetaScannerVisitor visitor)
+  throws IOException {
+    metaScan(configuration, visitor, EMPTY_START_ROW);
+  }
+
+  /**
+   * Scans the meta table and calls a visitor on each RowResult. Uses a table
+   * name to locate meta regions.
+   * 
+   * @param configuration
+   * @param visitor
+   * @param tableName
+   * @throws IOException
+   */
+  public static void metaScan(HBaseConfiguration configuration,
+      MetaScannerVisitor visitor, byte[] tableName)
+  throws IOException {
+    HConnection connection = HConnectionManager.getConnection(configuration);
+    HRegionLocation metaLocation = null;
+    boolean toContinue = true;
+    byte [] startRow = Bytes.equals(tableName, EMPTY_START_ROW)? tableName:
+      HRegionInfo.createRegionName(tableName, null, NINES);
+      
+    // Scan over the each meta region
+    do {
+      ScannerCallable callable = new ScannerCallable(connection,
+        META_TABLE_NAME, COL_REGIONINFO_ARRAY, tableName, LATEST_TIMESTAMP,
+        null);
+      try {
+        // Open scanner
+        connection.getRegionServerWithRetries(callable);
+        metaLocation = connection.locateRegion(META_TABLE_NAME, startRow);
+        while (toContinue) {
+          RowResult rowResult = connection.getRegionServerWithRetries(callable);
+          if (rowResult == null || rowResult.size() == 0) {
+            break;
+          }
+          HRegionInfo info = Writables.
+            getHRegionInfo(rowResult.get(COL_REGIONINFO));
+          toContinue = visitor.processRow(rowResult, metaLocation, info);
+        }
+        // Advance the startRow to the end key of the current region
+        startRow = callable.getHRegionInfo().getEndKey();
+      } finally {
+        // Close scanner
+        callable.setClose();
+        connection.getRegionServerWithRetries(callable);
+      }
+    } while (Bytes.compareTo(startRow, LAST_ROW) != 0);
+  }
+
+  /**
+   * Visitor class called to process each row of the .META. table
+   */
+  protected interface MetaScannerVisitor {
+
+    /**
+     * Visitor method that accepts a RowResult and the meta region location.
+     * Implementations can return false to stop the region's loop if it becomes
+     * unnecessary for some reason.
+     * 
+     * @param rowResult
+     * @param metaLocation
+     * @return A boolean to know if it should continue to loop in the region
+     * @throws IOException
+     */
+    public boolean processRow(RowResult rowResult,
+        HRegionLocation metaLocation, HRegionInfo info) throws IOException;
+  }
+}