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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.regionserver;
19  
20  import java.rmi.UnexpectedException;
21  import java.util.List;
22  
23  import org.apache.hadoop.classification.InterfaceAudience;
24  import org.apache.hadoop.hbase.Cell;
25  import org.apache.hadoop.hbase.io.HeapSize;
26  
27  /**
28   * The MemStore holds in-memory modifications to the Store. Modifications are {@link Cell}s.
29   * <p>
30   * The MemStore functions should not be called in parallel. Callers should hold write and read
31   * locks. This is done in {@link HStore}.
32   * </p>
33   */
34  @InterfaceAudience.Private
35  public interface MemStore extends HeapSize {
36  
37    /**
38     * Creates a snapshot of the current memstore. Snapshot must be cleared by call to
39     * {@link #clearSnapshot(long)}.
40     * @return {@link MemStoreSnapshot}
41     */
42    MemStoreSnapshot snapshot();
43  
44    /**
45     * Clears the current snapshot of the Memstore.
46     * @param id
47     * @see #snapshot()
48     */
49    void clearSnapshot(long id) throws UnexpectedException;
50  
51    /**
52     * On flush, how much memory we will clear.
53     * Flush will first clear out the data in snapshot if any (It will take a second flush
54     * invocation to clear the current Cell set). If snapshot is empty, current
55     * Cell set will be flushed.
56     *
57     * @return size of data that is going to be flushed
58     */
59    long getFlushableSize();
60  
61    /**
62     * Write an update
63     * @param cell
64     * @return approximate size of the passed key and value.
65     */
66    long add(final Cell cell);
67  
68    /**
69     * @return Oldest timestamp of all the Cells in the MemStore
70     */
71    long timeOfOldestEdit();
72  
73    /**
74     * Remove n key from the memstore. Only kvs that have the same key and the same memstoreTS are
75     * removed. It is ok to not update timeRangeTracker in this call.
76     * @param cell
77     */
78    void rollback(final Cell cell);
79  
80    /**
81     * Write a delete
82     * @param deleteCell
83     * @return approximate size of the passed key and value.
84     */
85    long delete(final Cell deleteCell);
86  
87    /**
88     * Find the key that matches <i>row</i> exactly, or the one that immediately precedes it. The
89     * target row key is set in state.
90     * @param state column/delete tracking state
91     */
92    void getRowKeyAtOrBefore(final GetClosestRowBeforeTracker state);
93  
94    /**
95     * Given the specs of a column, update it, first by inserting a new record,
96     * then removing the old one.  Since there is only 1 KeyValue involved, the memstoreTS
97     * will be set to 0, thus ensuring that they instantly appear to anyone. The underlying
98     * store will ensure that the insert/delete each are atomic. A scanner/reader will either
99     * get the new value, or the old value and all readers will eventually only see the new
100    * value after the old was removed.
101    *
102    * @param row
103    * @param family
104    * @param qualifier
105    * @param newValue
106    * @param now
107    * @return Timestamp
108    */
109   long updateColumnValue(byte[] row, byte[] family, byte[] qualifier, long newValue, long now);
110 
111   /**
112    * Update or insert the specified cells.
113    * <p>
114    * For each Cell, insert into MemStore. This will atomically upsert the value for that
115    * row/family/qualifier. If a Cell did already exist, it will then be removed.
116    * <p>
117    * Currently the memstoreTS is kept at 0 so as each insert happens, it will be immediately
118    * visible. May want to change this so it is atomic across all KeyValues.
119    * <p>
120    * This is called under row lock, so Get operations will still see updates atomically. Scans will
121    * only see each KeyValue update as atomic.
122    * @param cells
123    * @param readpoint readpoint below which we can safely remove duplicate Cells.
124    * @return change in memstore size
125    */
126   long upsert(Iterable<Cell> cells, long readpoint);
127 
128   /**
129    * @return scanner over the memstore. This might include scanner over the snapshot when one is
130    * present.
131    */
132   List<KeyValueScanner> getScanners(long readPt);
133 
134   /**
135    * @return Total memory occupied by this MemStore.
136    */
137   long size();
138 }