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1   /**
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  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,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  package org.apache.hadoop.hbase.regionserver;
20  
21  import java.io.IOException;
22  import java.util.List;
23  
24  import org.apache.hadoop.hbase.classification.InterfaceAudience;
25  import org.apache.hadoop.hbase.classification.InterfaceStability;
26  import org.apache.hadoop.hbase.Cell;
27  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
28  import org.apache.hadoop.hbase.HRegionInfo;
29  
30  /**
31   * RegionScanner describes iterators over rows in an HRegion.
32   */
33  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
34  @InterfaceStability.Stable
35  public interface RegionScanner extends InternalScanner {
36    /**
37     * @return The RegionInfo for this scanner.
38     */
39    HRegionInfo getRegionInfo();
40  
41    /**
42     * @return True if a filter indicates that this scanner will return no further rows.
43     * @throws IOException in case of I/O failure on a filter.
44     */
45    boolean isFilterDone() throws IOException;
46  
47    /**
48     * Do a reseek to the required row. Should not be used to seek to a key which
49     * may come before the current position. Always seeks to the beginning of a
50     * row boundary.
51     *
52     * @throws IOException
53     * @throws IllegalArgumentException
54     *           if row is null
55     *
56     */
57    boolean reseek(byte[] row) throws IOException;
58  
59    /**
60     * @return The preferred max buffersize. See 
61     * {@link org.apache.hadoop.hbase.client.Scan#setMaxResultSize(long)}
62     */
63    long getMaxResultSize();
64  
65    /**
66     * @return The Scanner's MVCC readPt see {@link MultiVersionConsistencyControl}
67     */
68    long getMvccReadPoint();
69  
70    /**
71     * Grab the next row's worth of values with the default limit on the number of values
72     * to return.
73     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
74     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
75     * Caller should maintain and update metrics.
76     * See {@link #nextRaw(List, int)}
77     * @param result return output array
78     * @return true if more rows exist after this one, false if scanner is done
79     * @throws IOException e
80     */
81    boolean nextRaw(List<Cell> result) throws IOException;
82  
83    /**
84     * Grab the next row's worth of values with a limit on the number of values
85     * to return.
86     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
87     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
88     * Example:
89     * <code><pre>
90     * HRegion region = ...;
91     * RegionScanner scanner = ...
92     * MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
93     * region.startRegionOperation();
94     * try {
95     *   synchronized(scanner) {
96     *     ...
97     *     boolean moreRows = scanner.nextRaw(values);
98     *     ...
99     *   }
100    * } finally {
101    *   region.closeRegionOperation();
102    * }
103    * </pre></code>
104    * @param result return output array
105    * @param limit limit on row count to get
106    * @return true if more rows exist after this one, false if scanner is done
107    * @throws IOException e
108    */
109   boolean nextRaw(List<Cell> result, int limit) throws IOException;
110 }