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1   /**
2    * Copyright The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one or more
5    * contributor license agreements. See the NOTICE file distributed with this
6    * work for additional information regarding copyright ownership. The ASF
7    * licenses this file to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance with the License.
9    * You may obtain a copy of the License at
10   *
11   * http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
16   * License for the specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.apache.hadoop.hbase.client;
20  
21  import java.io.IOException;
22  
23  import org.apache.commons.logging.Log;
24  import org.apache.commons.logging.LogFactory;
25  import org.apache.hadoop.classification.InterfaceAudience;
26  import org.apache.hadoop.classification.InterfaceStability;
27  import org.apache.hadoop.conf.Configuration;
28  import org.apache.hadoop.hbase.Cell;
29  import org.apache.hadoop.hbase.HConstants;
30  import org.apache.hadoop.hbase.KeyValueUtil;
31  import org.apache.hadoop.hbase.TableName;
32  import org.apache.hadoop.hbase.ipc.PayloadCarryingRpcController;
33  import org.apache.hadoop.hbase.ipc.RpcControllerFactory;
34  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
35  import org.apache.hadoop.hbase.protobuf.RequestConverter;
36  import org.apache.hadoop.hbase.protobuf.ResponseConverter;
37  import org.apache.hadoop.hbase.protobuf.generated.ClientProtos.ScanRequest;
38  import org.apache.hadoop.hbase.protobuf.generated.ClientProtos.ScanResponse;
39  import org.apache.hadoop.hbase.util.Bytes;
40  
41  import com.google.protobuf.ServiceException;
42  
43  /**
44   * Client scanner for small scan. Generally, only one RPC is called to fetch the
45   * scan results, unless the results cross multiple regions or the row count of
46   * results excess the caching.
47   * 
48   * For small scan, it will get better performance than {@link ClientScanner}
49   */
50  @InterfaceAudience.Public
51  @InterfaceStability.Evolving
52  public class ClientSmallScanner extends ClientScanner {
53    private final Log LOG = LogFactory.getLog(this.getClass());
54    private RegionServerCallable<Result[]> smallScanCallable = null;
55    // When fetching results from server, skip the first result if it has the same
56    // row with this one
57    private byte[] skipRowOfFirstResult = null;
58  
59    /**
60     * Create a new ClientSmallScanner for the specified table. An HConnection
61     * will be retrieved using the passed Configuration. Note that the passed
62     * {@link Scan} 's start row maybe changed.
63     * 
64     * @param conf The {@link Configuration} to use.
65     * @param scan {@link Scan} to use in this scanner
66     * @param tableName The table that we wish to rangeGet
67     * @throws IOException
68     */
69    public ClientSmallScanner(final Configuration conf, final Scan scan,
70        final TableName tableName) throws IOException {
71      this(conf, scan, tableName, HConnectionManager.getConnection(conf));
72    }
73  
74    /**
75     * Create a new ClientSmallScanner for the specified table. An HConnection
76     * will be retrieved using the passed Configuration. Note that the passed
77     * {@link Scan} 's start row maybe changed.
78     * @param conf
79     * @param scan
80     * @param tableName
81     * @param connection
82     * @throws IOException
83     */
84    public ClientSmallScanner(final Configuration conf, final Scan scan,
85        final TableName tableName, HConnection connection) throws IOException {
86      this(conf, scan, tableName, connection, RpcRetryingCallerFactory.instantiate(conf),
87          RpcControllerFactory.instantiate(conf));
88    }
89  
90    /**
91     * Create a new ShortClientScanner for the specified table Note that the
92     * passed {@link Scan}'s start row maybe changed changed.
93     * 
94     * @param conf The {@link Configuration} to use.
95     * @param scan {@link Scan} to use in this scanner
96     * @param tableName The table that we wish to rangeGet
97     * @param connection Connection identifying the cluster
98     * @param rpcFactory
99     * @param controllerFactory 
100    * @throws IOException
101    */
102   public ClientSmallScanner(final Configuration conf, final Scan scan, final TableName tableName,
103       HConnection connection, RpcRetryingCallerFactory rpcFactory,
104       RpcControllerFactory controllerFactory) throws IOException {
105     super(conf, scan, tableName, connection, rpcFactory, controllerFactory);
106   }
107 
108   @Override
109   protected void initializeScannerInConstruction() throws IOException {
110     // No need to initialize the scanner when constructing instance, do it when
111     // calling next(). Do nothing here.
112   }
113 
114   /**
115    * Gets a scanner for following scan. Move to next region or continue from the
116    * last result or start from the start row.
117    * @param nbRows
118    * @param done true if Server-side says we're done scanning.
119    * @param currentRegionDone true if scan is over on current region
120    * @return true if has next scanner
121    * @throws IOException
122    */
123   private boolean nextScanner(int nbRows, final boolean done,
124       boolean currentRegionDone) throws IOException {
125     // Where to start the next getter
126     byte[] localStartKey;
127     int cacheNum = nbRows;
128     skipRowOfFirstResult = null;
129     // if we're at end of table, close and return false to stop iterating
130     if (this.currentRegion != null && currentRegionDone) {
131       byte[] endKey = this.currentRegion.getEndKey();
132       if (endKey == null || Bytes.equals(endKey, HConstants.EMPTY_BYTE_ARRAY)
133           || checkScanStopRow(endKey) || done) {
134         close();
135         if (LOG.isDebugEnabled()) {
136           LOG.debug("Finished with small scan at " + this.currentRegion);
137         }
138         return false;
139       }
140       localStartKey = endKey;
141       if (LOG.isDebugEnabled()) {
142         LOG.debug("Finished with region " + this.currentRegion);
143       }
144     } else if (this.lastResult != null) {
145       localStartKey = this.lastResult.getRow();
146       skipRowOfFirstResult = this.lastResult.getRow();
147       cacheNum++;
148     } else {
149       localStartKey = this.scan.getStartRow();
150     }
151 
152     if (LOG.isTraceEnabled()) {
153       LOG.trace("Advancing internal small scanner to startKey at '"
154           + Bytes.toStringBinary(localStartKey) + "'");
155     }
156     smallScanCallable = getSmallScanCallable(
157         scan, getConnection(), getTable(), localStartKey, cacheNum, rpcControllerFactory);
158     if (this.scanMetrics != null && skipRowOfFirstResult == null) {
159       this.scanMetrics.countOfRegions.incrementAndGet();
160     }
161     return true;
162   }
163 
164   static RegionServerCallable<Result[]> getSmallScanCallable(
165       final Scan sc, HConnection connection, TableName table, byte[] localStartKey,
166       final int cacheNum, final RpcControllerFactory rpcControllerFactory) throws IOException { 
167     sc.setStartRow(localStartKey);
168     RegionServerCallable<Result[]> callable = new RegionServerCallable<Result[]>(
169         connection, table, sc.getStartRow()) {
170       public Result[] call() throws IOException {
171         ScanRequest request = RequestConverter.buildScanRequest(getLocation()
172           .getRegionInfo().getRegionName(), sc, cacheNum, true);
173         ScanResponse response = null;
174         PayloadCarryingRpcController controller = rpcControllerFactory.newController();
175         try {
176           controller.setPriority(getTableName());
177           response = getStub().scan(controller, request);
178           return ResponseConverter.getResults(controller.cellScanner(),
179               response);
180         } catch (ServiceException se) {
181           throw ProtobufUtil.getRemoteException(se);
182         }
183       }
184     };
185     return callable;
186   }
187 
188   @Override
189   public Result next() throws IOException {
190     // If the scanner is closed and there's nothing left in the cache, next is a
191     // no-op.
192     if (cache.size() == 0 && this.closed) {
193       return null;
194     }
195     if (cache.size() == 0) {
196       Result[] values = null;
197       long remainingResultSize = maxScannerResultSize;
198       int countdown = this.caching;
199       boolean currentRegionDone = false;
200       // Values == null means server-side filter has determined we must STOP
201       while (remainingResultSize > 0 && countdown > 0
202           && nextScanner(countdown, values == null, currentRegionDone)) {
203         // Server returns a null values if scanning is to stop. Else,
204         // returns an empty array if scanning is to go on and we've just
205         // exhausted current region.
206         values = this.caller.callWithRetries(smallScanCallable);
207         this.currentRegion = smallScanCallable.getHRegionInfo();
208         long currentTime = System.currentTimeMillis();
209         if (this.scanMetrics != null) {
210           this.scanMetrics.sumOfMillisSecBetweenNexts.addAndGet(currentTime
211               - lastNext);
212         }
213         lastNext = currentTime;
214         if (values != null && values.length > 0) {
215           for (int i = 0; i < values.length; i++) {
216             Result rs = values[i];
217             if (i == 0 && this.skipRowOfFirstResult != null
218                 && Bytes.equals(skipRowOfFirstResult, rs.getRow())) {
219               // Skip the first result
220               continue;
221             }
222             cache.add(rs);
223             for (Cell kv : rs.rawCells()) {
224               remainingResultSize -= KeyValueUtil.ensureKeyValue(kv).heapSize();
225             }
226             countdown--;
227             this.lastResult = rs;
228           }
229         }
230         currentRegionDone = countdown > 0;
231       }
232     }
233 
234     if (cache.size() > 0) {
235       return cache.poll();
236     }
237     // if we exhausted this scanner before calling close, write out the scan
238     // metrics
239     writeScanMetrics();
240     return null;
241   }
242 
243   @Override
244   public void close() {
245     if (!scanMetricsPublished) writeScanMetrics();
246     closed = true;
247   }
248 }