package brickhouse.udf.hll;
/**
* Copyright 2012,2013 Klout, Inc
*
* 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.
*
**/
import java.io.IOException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator.AggregationBuffer;
import org.apache.log4j.Logger;
import com.clearspring.analytics.stream.cardinality.CardinalityMergeException;
import com.clearspring.analytics.stream.cardinality.HyperLogLogPlus;
import com.clearspring.analytics.stream.cardinality.ICardinality;
public class HLLBuffer implements AggregationBuffer {
private static final Logger LOG = Logger.getLogger(HLLBuffer.class);
private ICardinality hll;
private int precision;
public HLLBuffer() {
hll = null;
precision = 0;
}
public boolean isReady() {
return precision != 0;
}
public void init(int precision) {
this.precision = precision;
hll = new HyperLogLogPlus(precision);
}
public void reset() {
hll = null;
precision = 0;
}
public void addItem(String str) {
hll.offer(str);
}
public void merge(byte[] buffer) throws IOException,
CardinalityMergeException {
if (buffer == null) {
return;
}
ICardinality other = HyperLogLogPlus.Builder.build(buffer);
// if hll estimator hasn't been allocated yet, just set it equal to the partial
if (hll == null) {
LOG.debug("hll is null; other.sizeof = " + other.sizeof());
hll = other;
precision = (int) Math.ceil(Math.log(other.sizeof())/Math.log(2.0));
LOG.debug("precision set to: " + precision);
} else {
hll.merge(other);
}
}
public byte[] getPartial() throws IOException {
if (hll == null) {
return null;
}
return hll.getBytes();
}
}