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 org.apache.hadoop.hbase.classification.InterfaceAudience;
21 import org.apache.hadoop.hbase.util.ByteRange;
22
23 /**
24 * A memstore-local allocation buffer.
25 * <p>
26 * The MemStoreLAB is basically a bump-the-pointer allocator that allocates big (2MB) chunks from
27 * and then doles it out to threads that request slices into the array.
28 * <p>
29 * The purpose of this is to combat heap fragmentation in the regionserver. By ensuring that all
30 * KeyValues in a given memstore refer only to large chunks of contiguous memory, we ensure that
31 * large blocks get freed up when the memstore is flushed.
32 * <p>
33 * Without the MSLAB, the byte array allocated during insertion end up interleaved throughout the
34 * heap, and the old generation gets progressively more fragmented until a stop-the-world compacting
35 * collection occurs.
36 * <p>
37 */
38 @InterfaceAudience.Private
39 public interface MemStoreLAB {
40
41 /**
42 * Allocate a slice of the given length. If the size is larger than the maximum size specified for
43 * this allocator, returns null.
44 * @param size
45 * @return {@link ByteRange}
46 */
47 ByteRange allocateBytes(int size);
48
49 /**
50 * Close instance since it won't be used any more, try to put the chunks back to pool
51 */
52 void close();
53
54 /**
55 * Called when opening a scanner on the data of this MemStoreLAB
56 */
57 void incScannerCount();
58
59 /**
60 * Called when closing a scanner on the data of this MemStoreLAB
61 */
62 void decScannerCount();
63 }