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1   /**
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *     http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  package org.apache.hadoop.hbase.regionserver;
20  
21  import java.io.IOException;
22  
23  import org.apache.hadoop.classification.InterfaceAudience;
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  @InterfaceAudience.Private
50  public interface ColumnTracker {
51    /**
52     * Keeps track of the number of versions for the columns asked for
53     * @param bytes
54     * @param offset
55     * @param length
56     * @param ttl The timeToLive to enforce.
57     * @param type The type of the KeyValue
58     * @param ignoreCount indicates if the KV needs to be excluded while counting
59     *   (used during compactions. We only count KV's that are older than all the
60     *   scanners' read points.)
61     * @return The match code instance.
62     * @throws IOException in case there is an internal consistency problem
63     *      caused by a data corruption.
64     */
65    ScanQueryMatcher.MatchCode checkColumn(byte[] bytes, int offset,
66        int length, long ttl, byte type, boolean ignoreCount)
67        throws IOException;
68  
69    /**
70     * Resets the Matcher
71     */
72    void reset();
73  
74    /**
75     *
76     * @return <code>true</code> when done.
77     */
78    boolean done();
79  
80    /**
81     * Used by matcher and scan/get to get a hint of the next column
82     * to seek to after checkColumn() returns SKIP.  Returns the next interesting
83     * column we want, or NULL there is none (wildcard scanner).
84     *
85     * Implementations aren't required to return anything useful unless the most recent
86     * call was to checkColumn() and the return code was SKIP.  This is pretty implementation
87     * detail-y, but optimizations are like that.
88     *
89     * @return null, or a ColumnCount that we should seek to
90     */
91    ColumnCount getColumnHint();
92  
93    /**
94     * Retrieve the MatchCode for the next row or column
95     */
96    MatchCode getNextRowOrNextColumn(
97      byte[] bytes, int offset, int qualLength
98    );
99  
100   /**
101    * Give the tracker a chance to declare it's done based on only the timestamp
102    * to allow an early out.
103    *
104    * @param timestamp
105    * @return <code>true</code> to early out based on timestamp.
106    */
107   boolean isDone(long timestamp);
108 }