| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.cassandra.utils; |
| |
| import java.io.IOException; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import org.apache.cassandra.io.util.DataOutputStreamPlus; |
| import org.apache.cassandra.utils.concurrent.Ref; |
| import org.apache.cassandra.utils.obs.IBitSet; |
| import org.apache.cassandra.utils.obs.OffHeapBitSet; |
| |
| public class FilterFactory |
| { |
| public static final IFilter AlwaysPresent = AlwaysPresentFilter.instance; |
| |
| private static final Logger logger = LoggerFactory.getLogger(FilterFactory.class); |
| private static final long BITSET_EXCESS = 20; |
| |
| /** |
| * @return A BloomFilter with the lowest practical false positive |
| * probability for the given number of elements. |
| */ |
| public static IFilter getFilter(long numElements, int targetBucketsPerElem) |
| { |
| int maxBucketsPerElement = Math.max(1, BloomCalculations.maxBucketsPerElement(numElements)); |
| int bucketsPerElement = Math.min(targetBucketsPerElem, maxBucketsPerElement); |
| if (bucketsPerElement < targetBucketsPerElem) |
| { |
| logger.warn("Cannot provide an optimal BloomFilter for {} elements ({}/{} buckets per element).", numElements, bucketsPerElement, targetBucketsPerElem); |
| } |
| BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement); |
| return createFilter(spec.K, numElements, spec.bucketsPerElement); |
| } |
| |
| /** |
| * @return The smallest BloomFilter that can provide the given false |
| * positive probability rate for the given number of elements. |
| * |
| * Asserts that the given probability can be satisfied using this |
| * filter. |
| */ |
| public static IFilter getFilter(long numElements, double maxFalsePosProbability) |
| { |
| assert maxFalsePosProbability <= 1.0 : "Invalid probability"; |
| if (maxFalsePosProbability == 1.0) |
| return FilterFactory.AlwaysPresent; |
| int bucketsPerElement = BloomCalculations.maxBucketsPerElement(numElements); |
| BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement, maxFalsePosProbability); |
| return createFilter(spec.K, numElements, spec.bucketsPerElement); |
| } |
| |
| @SuppressWarnings("resource") |
| private static IFilter createFilter(int hash, long numElements, int bucketsPer) |
| { |
| long numBits = (numElements * bucketsPer) + BITSET_EXCESS; |
| IBitSet bitset = new OffHeapBitSet(numBits); |
| return new BloomFilter(hash, bitset); |
| } |
| |
| private static class AlwaysPresentFilter implements IFilter |
| { |
| public static final AlwaysPresentFilter instance = new AlwaysPresentFilter(); |
| |
| private AlwaysPresentFilter() { } |
| |
| public boolean isPresent(FilterKey key) |
| { |
| return true; |
| } |
| |
| public void add(FilterKey key) { } |
| |
| public void clear() { } |
| |
| public void close() { } |
| |
| public IFilter sharedCopy() |
| { |
| return this; |
| } |
| |
| public Throwable close(Throwable accumulate) |
| { |
| return accumulate; |
| } |
| |
| public void addTo(Ref.IdentityCollection identities) |
| { |
| } |
| |
| public long serializedSize(boolean oldSerializationFormat) { return 0; } |
| |
| @Override |
| public void serialize(DataOutputStreamPlus out, boolean oldSerializationFormat) throws IOException |
| { |
| // no-op |
| } |
| |
| @Override |
| public long offHeapSize() |
| { |
| return 0; |
| } |
| |
| @Override |
| public boolean isInformative() |
| { |
| return false; |
| } |
| } |
| } |