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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  import java.io.IOException;
23  
24  import org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode;
25  
26  /**
27   * Implementing classes of this interface will be used for the tracking
28   * and enforcement of columns and numbers of versions and timeToLive during
29   * the course of a Get or Scan operation.
30   * <p>
31   * Currently there are two different types of Store/Family-level queries.
32   * <ul><li>{@link ExplicitColumnTracker} is used when the query specifies
33   * one or more column qualifiers to return in the family.
34   * <p>
35   * This class is utilized by {@link ScanQueryMatcher} through two methods:
36   * <ul><li>{@link #checkColumn} is called when a Put satisfies all other
37   * conditions of the query.  This method returns a {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode} to define
38   * what action should be taken.
39   * <li>{@link #update} is called at the end of every StoreFile or memstore.
40   * <p>
41   * This class is NOT thread-safe as queries are never multi-threaded
42   */
43  public interface ColumnTracker {
44    /**
45     * Keeps track of the number of versions for the columns asked for
46     * @param bytes
47     * @param offset
48     * @param length
49     * @param ttl The timeToLive to enforce.
50     * @param ignoreCount indicates if the KV needs to be excluded while counting
51     *   (used during compactions. We only count KV's that are older than all the
52     *   scanners' read points.)
53     * @return The match code instance.
54     * @throws IOException in case there is an internal consistency problem
55     *      caused by a data corruption.
56     */
57    public ScanQueryMatcher.MatchCode checkColumn(byte [] bytes, int offset,
58        int length, long ttl, boolean ignoreCount) throws IOException;
59  
60    /**
61     * Updates internal variables in between files
62     */
63    public void update();
64  
65    /**
66     * Resets the Matcher
67     */
68    public void reset();
69  
70    /**
71     *
72     * @return <code>true</code> when done.
73     */
74    public boolean done();
75  
76    /**
77     * Used by matcher and scan/get to get a hint of the next column
78     * to seek to after checkColumn() returns SKIP.  Returns the next interesting
79     * column we want, or NULL there is none (wildcard scanner).
80     *
81     * Implementations aren't required to return anything useful unless the most recent
82     * call was to checkColumn() and the return code was SKIP.  This is pretty implementation
83     * detail-y, but optimizations are like that.
84     *
85     * @return null, or a ColumnCount that we should seek to
86     */
87    public ColumnCount getColumnHint();
88  
89    /**
90     * Retrieve the MatchCode for the next row or column
91     */
92    public MatchCode getNextRowOrNextColumn(byte[] bytes, int offset,
93        int qualLength);
94  
95    /**
96     * Give the tracker a chance to declare it's done based on only the timestamp
97     * to allow an early out.
98     *
99     * @param timestamp
100    * @return <code>true</code> to early out based on timestamp.
101    */
102   public boolean isDone(long timestamp);
103 }