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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.Cell;
25  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
26  import org.apache.hadoop.hbase.HRegionInfo;
27  import org.apache.hadoop.hbase.classification.InterfaceAudience;
28  import org.apache.hadoop.hbase.classification.InterfaceStability;
29  
30  /**
31   * RegionScanner describes iterators over rows in an HRegion.
32   */
33  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
34  @InterfaceStability.Evolving
35  public interface RegionScanner extends InternalScanner, Shipper {
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     * @return The limit on the number of cells to retrieve on each call to next(). See
72     *         {@link org.apache.hadoop.hbase.client.Scan#setBatch(int)}
73     */
74    int getBatch();
75  
76    /**
77     * Grab the next row's worth of values. This is a special internal method to be called from
78     * coprocessor hooks to avoid expensive setup. Caller must set the thread's readpoint, start and
79     * close a region operation, an synchronize on the scanner object. Caller should maintain and
80     * update metrics. See {@link #nextRaw(List, ScannerContext)}
81     * @param result return output array
82     * @return true if more rows exist after this one, false if scanner is done
83     * @throws IOException e
84     */
85    boolean nextRaw(List<Cell> result) throws IOException;
86    
87    /**
88     * Grab the next row's worth of values. The {@link ScannerContext} is used to enforce and track
89     * any limits associated with this call. Any progress that exists in the {@link ScannerContext}
90     * prior to calling this method will be LOST if {@link ScannerContext#getKeepProgress()} is false.
91     * Upon returning from this method, the {@link ScannerContext} will contain information about the
92     * progress made towards the limits. This is a special internal method to be called from
93     * coprocessor hooks to avoid expensive setup. Caller must set the thread's readpoint, start and
94     * close a region operation, an synchronize on the scanner object. Example: <code>
95     * HRegion region = ...;
96     * RegionScanner scanner = ...
97     * MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
98     * region.startRegionOperation();
99     * try {
100    *   synchronized(scanner) {
101    *     ...
102    *     boolean moreRows = scanner.nextRaw(values);
103    *     ...
104    *   }
105    * } finally {
106    *   region.closeRegionOperation();
107    * }
108    * </code>
109    * @param result return output array
110    * @param scannerContext The {@link ScannerContext} instance encapsulating all limits that should
111    *          be tracked during calls to this method. The progress towards these limits can be
112    *          tracked within this instance.
113    * @return true if more rows exist after this one, false if scanner is done
114    * @throws IOException e
115    */
116   boolean nextRaw(List<Cell> result, ScannerContext scannerContext)
117       throws IOException;
118 }