View Javadoc

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 type The type of the KeyValue
51     * @param ignoreCount indicates if the KV needs to be excluded while counting
52     *   (used during compactions. We only count KV's that are older than all the
53     *   scanners' read points.)
54     * @return The match code instance.
55     * @throws IOException in case there is an internal consistency problem
56     *      caused by a data corruption.
57     */
58    public ScanQueryMatcher.MatchCode checkColumn(byte[] bytes, int offset,
59        int length, long ttl, byte type, boolean ignoreCount)
60        throws IOException;
61  
62    /**
63     * Updates internal variables in between files
64     */
65    public void update();
66  
67    /**
68     * Resets the Matcher
69     */
70    public void reset();
71  
72    /**
73     *
74     * @return <code>true</code> when done.
75     */
76    public boolean done();
77  
78    /**
79     * Used by matcher and scan/get to get a hint of the next column
80     * to seek to after checkColumn() returns SKIP.  Returns the next interesting
81     * column we want, or NULL there is none (wildcard scanner).
82     *
83     * Implementations aren't required to return anything useful unless the most recent
84     * call was to checkColumn() and the return code was SKIP.  This is pretty implementation
85     * detail-y, but optimizations are like that.
86     *
87     * @return null, or a ColumnCount that we should seek to
88     */
89    public ColumnCount getColumnHint();
90  
91    /**
92     * Retrieve the MatchCode for the next row or column
93     */
94    public MatchCode getNextRowOrNextColumn(byte[] bytes, int offset,
95        int qualLength);
96  
97    /**
98     * Give the tracker a chance to declare it's done based on only the timestamp
99     * to allow an early out.
100    *
101    * @param timestamp
102    * @return <code>true</code> to early out based on timestamp.
103    */
104   public boolean isDone(long timestamp);
105 }