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1   /**
2    * Copyright 2010 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.filter;
21  
22  import org.apache.hadoop.hbase.KeyValue;
23  
24  import java.io.DataInput;
25  import java.io.DataOutput;
26  import java.io.IOException;
27  import java.util.List;
28  
29  /**
30   * Implementation of Filter interface that limits results to a specific page
31   * size. It terminates scanning once the number of filter-passed rows is >
32   * the given page size.
33   * <p>
34   * Note that this filter cannot guarantee that the number of results returned
35   * to a client are <= page size. This is because the filter is applied
36   * separately on different region servers. It does however optimize the scan of
37   * individual HRegions by making sure that the page size is never exceeded
38   * locally.
39   */
40  public class PageFilter extends FilterBase {
41    private long pageSize = Long.MAX_VALUE;
42    private int rowsAccepted = 0;
43  
44    /**
45     * Default constructor, filters nothing. Required though for RPC
46     * deserialization.
47     */
48    public PageFilter() {
49      super();
50    }
51  
52    /**
53     * Constructor that takes a maximum page size.
54     *
55     * @param pageSize Maximum result size.
56     */
57    public PageFilter(final long pageSize) {
58      this.pageSize = pageSize;
59    }
60  
61    public long getPageSize() {
62      return pageSize;
63    }
64  
65    public boolean filterAllRemaining() {
66      return this.rowsAccepted >= this.pageSize;
67    }
68  
69    public boolean filterRow() {
70      this.rowsAccepted++;
71      return this.rowsAccepted > this.pageSize;
72    }
73  
74    public void readFields(final DataInput in) throws IOException {
75      this.pageSize = in.readLong();
76    }
77  
78    public void write(final DataOutput out) throws IOException {
79      out.writeLong(pageSize);
80    }
81  }