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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.SortedSet;
24  
25  import org.apache.commons.lang.NotImplementedException;
26  import org.apache.hadoop.hbase.KeyValue;
27  import org.apache.hadoop.hbase.client.Scan;
28  
29  /**
30   * A "non-lazy" scanner which always does a real seek operation. Most scanners
31   * are inherited from this class.
32   */
33  public abstract class NonLazyKeyValueScanner implements KeyValueScanner {
34  
35    @Override
36    public boolean requestSeek(KeyValue kv, boolean forward, boolean useBloom)
37        throws IOException {
38      return doRealSeek(this, kv, forward);
39    }
40  
41    @Override
42    public boolean realSeekDone() {
43      return true;
44    }
45  
46    @Override
47    public void enforceSeek() throws IOException {
48      throw new NotImplementedException("enforceSeek must not be called on a " +
49          "non-lazy scanner");
50    }
51  
52    public static boolean doRealSeek(KeyValueScanner scanner,
53        KeyValue kv, boolean forward) throws IOException {
54      return forward ? scanner.reseek(kv) : scanner.seek(kv);
55    }
56  
57    @Override
58    public boolean shouldUseScanner(Scan scan, SortedSet<byte[]> columns,
59        long oldestUnexpiredTS) {
60      // No optimizations implemented by default.
61      return true;
62    }
63  
64    @Override
65    public boolean isFileScanner() {
66      // Not a file by default.
67      return false;
68    }
69  }