/*
* Copyright (c) 2010 Yahoo! Inc. All rights reserved.
*
* Licensed 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. See accompanying LICENSE file.
*/
package voldemort.performance.benchmark.generator;
import voldemort.utils.FnvHashFunction;
/**
* A generator of a Zipfian distribution. It produces a sequence of items, such
* that some items are more popular than others, according to a Zipfian
* distribution.
*
* Unlike @ZipfianGenerator, this class scatters the "popular" items across the
* item space. Use this, instead of @ZipfianGenerator, if you don't want the
* head of the distribution (the popular items) clustered together.
*/
public class ScrambledZipfianGenerator extends IntegerGenerator {
public static final double ZETAN = 52.93805640344461;
public static final long ITEM_COUNT = 10000000000L;
private ZipfianGenerator generator;
private long min, max, itemCount;
private FnvHashFunction hash;
public ScrambledZipfianGenerator(long items) {
this(0, items - 1);
}
public ScrambledZipfianGenerator(long min, long max) {
this(min, max, ZipfianGenerator.ZIPFIAN_CONSTANT);
}
public ScrambledZipfianGenerator(long min, long max, double zipfianConstant) {
this.min = min;
this.max = max;
this.itemCount = this.max - this.min + 1;
generator = new ZipfianGenerator(0, ITEM_COUNT, zipfianConstant, ZETAN);
hash = new FnvHashFunction();
}
@Override
public int nextInt() {
return (int) nextLong();
}
public long nextLong() {
long ret = generator.nextLong();
ret = min + hash.hash64(ret) % itemCount;
setLastInt((int) ret);
return ret;
}
}