/*
* 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.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.cassandra.utils.obs.IBitSet;
import org.apache.cassandra.utils.obs.OffHeapBitSet;
import org.apache.cassandra.utils.obs.OpenBitSet;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class FilterFactory
{
public static final IFilter AlwaysPresent = new AlwaysPresentFilter();
private static final Logger logger = LoggerFactory.getLogger(FilterFactory.class);
private static final long BITSET_EXCESS = 20;
public static void serialize(IFilter bf, DataOutput output) throws IOException
{
Murmur3BloomFilter.serializer.serialize((Murmur3BloomFilter) bf, output);
}
public static IFilter deserialize(DataInput input, boolean offheap) throws IOException
{
return Murmur3BloomFilter.serializer.deserialize(input, offheap);
}
/**
* @return A BloomFilter with the lowest practical false positive
* probability for the given number of elements.
*/
public static IFilter getFilter(long numElements, int targetBucketsPerElem, boolean offheap)
{
int maxBucketsPerElement = Math.max(1, BloomCalculations.maxBucketsPerElement(numElements));
int bucketsPerElement = Math.min(targetBucketsPerElem, maxBucketsPerElement);
if (bucketsPerElement < targetBucketsPerElem)
{
logger.warn(String.format("Cannot provide an optimal BloomFilter for %d elements (%d/%d buckets per element).", numElements, bucketsPerElement, targetBucketsPerElem));
}
BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement);
return createFilter(spec.K, numElements, spec.bucketsPerElement, offheap);
}
/**
* @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, boolean offheap)
{
assert maxFalsePosProbability <= 1.0 : "Invalid probability";
if (maxFalsePosProbability == 1.0)
return new AlwaysPresentFilter();
int bucketsPerElement = BloomCalculations.maxBucketsPerElement(numElements);
BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement, maxFalsePosProbability);
return createFilter(spec.K, numElements, spec.bucketsPerElement, offheap);
}
private static IFilter createFilter(int hash, long numElements, int bucketsPer, boolean offheap)
{
long numBits = (numElements * bucketsPer) + BITSET_EXCESS;
IBitSet bitset = offheap ? new OffHeapBitSet(numBits) : new OpenBitSet(numBits);
return new Murmur3BloomFilter(hash, bitset);
}
}