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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   * <ul><li>{@link ScanWildcardColumnTracker} is used when no columns are
35   * explicitly specified.
36   * <p>
37   * This class is utilized by {@link ScanQueryMatcher} mainly through two methods:
38   * <ul><li>{@link #checkColumn} is called when a Put satisfies all other
39   * conditions of the query.
40   * <ul><li>{@link #getNextRowOrNextColumn} is called whenever ScanQueryMatcher
41   * believes that the current column should be skipped (by timestamp, filter etc.)
42   * <p>
43   * These two methods returns a 
44   * {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode}
45   * to define what action should be taken.
46   * <p>
47   * This class is NOT thread-safe as queries are never multi-threaded
48   */
49  public interface ColumnTracker {
50    /**
51     * Keeps track of the number of versions for the columns asked for
52     * @param bytes
53     * @param offset
54     * @param length
55     * @param ttl The timeToLive to enforce.
56     * @param type The type of the KeyValue
57     * @param ignoreCount indicates if the KV needs to be excluded while counting
58     *   (used during compactions. We only count KV's that are older than all the
59     *   scanners' read points.)
60     * @return The match code instance.
61     * @throws IOException in case there is an internal consistency problem
62     *      caused by a data corruption.
63     */
64    public ScanQueryMatcher.MatchCode checkColumn(byte[] bytes, int offset,
65        int length, long ttl, byte type, boolean ignoreCount)
66        throws IOException;
67  
68    /**
69     * Resets the Matcher
70     */
71    public void reset();
72  
73    /**
74     *
75     * @return <code>true</code> when done.
76     */
77    public boolean done();
78  
79    /**
80     * Used by matcher and scan/get to get a hint of the next column
81     * to seek to after checkColumn() returns SKIP.  Returns the next interesting
82     * column we want, or NULL there is none (wildcard scanner).
83     *
84     * Implementations aren't required to return anything useful unless the most recent
85     * call was to checkColumn() and the return code was SKIP.  This is pretty implementation
86     * detail-y, but optimizations are like that.
87     *
88     * @return null, or a ColumnCount that we should seek to
89     */
90    public ColumnCount getColumnHint();
91  
92    /**
93     * Retrieve the MatchCode for the next row or column
94     */
95    public MatchCode getNextRowOrNextColumn(byte[] bytes, int offset,
96        int qualLength);
97  
98    /**
99     * Give the tracker a chance to declare it's done based on only the timestamp
100    * to allow an early out.
101    *
102    * @param timestamp
103    * @return <code>true</code> to early out based on timestamp.
104    */
105   public boolean isDone(long timestamp);
106 }