Package brickhouse.udf.hll

Source Code of brickhouse.udf.hll.HLLBuffer

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();
  }

}
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