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1   /**
2    * Copyright 2011 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.regionserver;
21  
22  import java.io.IOException;
23  import java.util.List;
24  
25  import org.apache.hadoop.hbase.HRegionInfo;
26  import org.apache.hadoop.hbase.KeyValue;
27  
28  /**
29   * RegionScanner describes iterators over rows in an HRegion.
30   */
31  public interface RegionScanner extends InternalScanner {
32    /**
33     * @return The RegionInfo for this scanner.
34     */
35    public HRegionInfo getRegionInfo();
36  
37    /**
38     * @return True if a filter indicates that this scanner will return no
39     *         further rows.
40     */
41    public boolean isFilterDone();
42  
43    /**
44     * Do a reseek to the required row. Should not be used to seek to a key which
45     * may come before the current position. Always seeks to the beginning of a
46     * row boundary.
47     *
48     * @throws IOException
49     * @throws IllegalArgumentException
50     *           if row is null
51     *
52     */
53    public boolean reseek(byte[] row) throws IOException;
54  
55    /**
56     * @return The Scanner's MVCC readPt see {@link MultiVersionConsistencyControl}
57     */
58    public long getMvccReadPoint();
59  
60    /**
61     * Grab the next row's worth of values with the default limit on the number of values
62     * to return.
63     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
64     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
65     * See {@link #nextRaw(List, int, String)}
66     * @param result return output array
67     * @param metric the metric name
68     * @return true if more rows exist after this one, false if scanner is done
69     * @throws IOException e
70     */
71    public boolean nextRaw(List<KeyValue> result, String metric) throws IOException;
72  
73    /**
74     * Grab the next row's worth of values with a limit on the number of values
75     * to return.
76     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
77     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
78     * Example:
79     * <code><pre>
80     * HRegion region = ...;
81     * RegionScanner scanner = ...
82     * MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
83     * region.startRegionOperation();
84     * try {
85     *   synchronized(scanner) {
86     *     ...
87     *     boolean moreRows = scanner.nextRaw(values);
88     *     ...
89     *   }
90     * } finally {
91     *   region.closeRegionOperation();
92     * }
93     * </pre></code>
94     * @param result return output array
95     * @param limit limit on row count to get
96     * @param metric the metric name
97     * @return true if more rows exist after this one, false if scanner is done
98     * @throws IOException e
99     */
100   public boolean nextRaw(List<KeyValue> result, int limit, String metric) throws IOException;
101 }