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.omid.tso;
19
20 import org.slf4j.Logger;
21 import org.slf4j.LoggerFactory;
22
23 /**
24 * Stores the mapping between a particular cell id and the commit timestamp
25 * of the last transaction that changed it.
26 *
27 * The mapping is implemented as a long -> long mapping, using a single long [].
28 * For a map of size N we create an array of size 2*N and store the keys
29 * on even indexes and values on odd indexes. The rationale is that we want
30 * queries to be fast and touch as least memory regions as possible.
31 *
32 * Each time an entry is removed, the caller updates the largestDeletedTimestamp
33 * if the entry's commit timestamp is greater than this value.
34 *
35 * TODO: improve garbage collection, right now an entry is picked at random
36 * (by hash) which could cause the eviction of a very recent timestamp
37 */
38
39 class CommitHashMap {
40
41 private static final Logger LOG = LoggerFactory.getLogger(CommitHashMap.class);
42
43 private final LongCache cellIdToCommitMap;
44
45 /**
46 * Constructs a new, empty hashtable with a default size of 1000
47 */
48 public CommitHashMap() {
49 this(1000);
50 }
51
52 /**
53 * Constructs a new, empty hashtable with the specified size
54 *
55 * @param size
56 * the initial size of the hashtable.
57 * @throws IllegalArgumentException
58 * if the size is less than zero.
59 */
60 public CommitHashMap(int size) {
61 if (size < 0) {
62 throw new IllegalArgumentException("Illegal size: " + size);
63 }
64
65 this.cellIdToCommitMap = new LongCache(size, 32);
66 LOG.info("CellId -> CommitTS map created with [{}] buckets (32 elems/bucket)", size);
67 }
68
69 public long getLatestWriteForCell(long hash) {
70 return cellIdToCommitMap.get(hash);
71 }
72
73 public long putLatestWriteForCell(long hash, long commitTimestamp) {
74 return cellIdToCommitMap.set(hash, commitTimestamp);
75 }
76 }