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.regionserver;
21
22 import java.io.IOException;
23
24 import org.apache.hadoop.hbase.KeyValue;
25
26 /**
27 * Scanner that returns the next KeyValue.
28 */
29 public interface KeyValueScanner {
30 /**
31 * Look at the next KeyValue in this scanner, but do not iterate scanner.
32 * @return the next KeyValue
33 */
34 public KeyValue peek();
35
36 /**
37 * Return the next KeyValue in this scanner, iterating the scanner
38 * @return the next KeyValue
39 */
40 public KeyValue next() throws IOException;
41
42 /**
43 * Seek the scanner at or after the specified KeyValue.
44 * @param key seek value
45 * @return true if scanner has values left, false if end of scanner
46 */
47 public boolean seek(KeyValue key) throws IOException;
48
49 /**
50 * Reseek the scanner at or after the specified KeyValue.
51 * This method is guaranteed to seek at or after the required key only if the
52 * key comes after the current position of the scanner. Should not be used
53 * to seek to a key which may come before the current position.
54 * @param key seek value (should be non-null)
55 * @return true if scanner has values left, false if end of scanner
56 */
57 public boolean reseek(KeyValue key) throws IOException;
58
59 /**
60 * Similar to {@link #seek} (or {@link #reseek} if forward is true) but only
61 * does a seek operation after checking that it is really necessary for the
62 * row/column combination specified by the kv parameter. This function was
63 * added to avoid unnecessary disk seeks on multi-column get queries using
64 * Bloom filter checking. Should only be used for queries where the set of
65 * columns is specified exactly.
66 */
67 public boolean seekExactly(KeyValue kv, boolean forward) throws IOException;
68
69 /**
70 * Get the sequence id associated with this KeyValueScanner. This is required
71 * for comparing multiple files to find out which one has the latest data.
72 * The default implementation for this would be to return 0. A file having
73 * lower sequence id will be considered to be the older one.
74 */
75 public long getSequenceID();
76
77 /**
78 * Close the KeyValue scanner.
79 */
80 public void close();
81 }