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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.classification.InterfaceAudience;
25  import org.apache.hadoop.hbase.Cell;
26  import org.apache.hadoop.hbase.HRegionInfo;
27  import org.apache.hadoop.hbase.client.Scan;
28  
29  /**
30   * RegionScanner describes iterators over rows in an HRegion.
31   */
32  @InterfaceAudience.Private
33  public interface RegionScanner extends InternalScanner {
34    /**
35     * @return The RegionInfo for this scanner.
36     */
37    HRegionInfo getRegionInfo();
38  
39    /**
40     * @return True if a filter indicates that this scanner will return no further rows.
41     * @throws IOException in case of I/O failure on a filter.
42     */
43    boolean isFilterDone() throws IOException;
44  
45    /**
46     * Do a reseek to the required row. Should not be used to seek to a key which
47     * may come before the current position. Always seeks to the beginning of a
48     * row boundary.
49     *
50     * @throws IOException
51     * @throws IllegalArgumentException
52     *           if row is null
53     *
54     */
55    boolean reseek(byte[] row) throws IOException;
56  
57    /**
58     * @return The preferred max buffersize. See {@link Scan#setMaxResultSize(long)}
59     */
60    long getMaxResultSize();
61  
62    /**
63     * @return The Scanner's MVCC readPt see {@link MultiVersionConsistencyControl}
64     */
65    long getMvccReadPoint();
66  
67    /**
68     * Grab the next row's worth of values with the default limit on the number of values
69     * to return.
70     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
71     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
72     * Caller should maintain and update metrics.
73     * See {@link #nextRaw(List, int)}
74     * @param result return output array
75     * @return true if more rows exist after this one, false if scanner is done
76     * @throws IOException e
77     */
78    boolean nextRaw(List<Cell> result) throws IOException;
79  
80    /**
81     * Grab the next row's worth of values with a limit on the number of values
82     * to return.
83     * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
84     * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
85     * Example:
86     * <code><pre>
87     * HRegion region = ...;
88     * RegionScanner scanner = ...
89     * MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
90     * region.startRegionOperation();
91     * try {
92     *   synchronized(scanner) {
93     *     ...
94     *     boolean moreRows = scanner.nextRaw(values);
95     *     ...
96     *   }
97     * } finally {
98     *   region.closeRegionOperation();
99     * }
100    * </pre></code>
101    * @param result return output array
102    * @param limit limit on row count to get
103    * @return true if more rows exist after this one, false if scanner is done
104    * @throws IOException e
105    */
106   boolean nextRaw(List<Cell> result, int limit) throws IOException;
107 }