1 /**
2 * Copyright 2009 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 /**
23 * Implementing classes of this interface will be used for the tracking
24 * and enforcement of columns and numbers of versions during the course of a
25 * Get or Scan operation.
26 * <p>
27 * Currently there are two different types of Store/Family-level queries.
28 * <ul><li>{@link ExplicitColumnTracker} is used when the query specifies
29 * one or more column qualifiers to return in the family.
30 * <p>
31 * This class is utilized by {@link ScanQueryMatcher} through two methods:
32 * <ul><li>{@link #checkColumn} is called when a Put satisfies all other
33 * conditions of the query. This method returns a {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode} to define
34 * what action should be taken.
35 * <li>{@link #update} is called at the end of every StoreFile or memstore.
36 * <p>
37 * This class is NOT thread-safe as queries are never multi-threaded
38 */
39 public interface ColumnTracker {
40 /**
41 * Keeps track of the number of versions for the columns asked for
42 * @param bytes
43 * @param offset
44 * @param length
45 * @return The match code instance.
46 */
47 public ScanQueryMatcher.MatchCode checkColumn(byte [] bytes, int offset, int length);
48
49 /**
50 * Updates internal variables in between files
51 */
52 public void update();
53
54 /**
55 * Resets the Matcher
56 */
57 public void reset();
58
59 /**
60 *
61 * @return <code>true</code> when done.
62 */
63 public boolean done();
64
65 /**
66 * Used by matcher and scan/get to get a hint of the next column
67 * to seek to after checkColumn() returns SKIP. Returns the next interesting
68 * column we want, or NULL there is none (wildcard scanner).
69 *
70 * Implementations aren't required to return anything useful unless the most recent
71 * call was to checkColumn() and the return code was SKIP. This is pretty implementation
72 * detail-y, but optimizations are like that.
73 *
74 * @return null, or a ColumnCount that we should seek to
75 */
76 public ColumnCount getColumnHint();
77 }