org.apache.datasketches.hllmap.package-info Maven / Gradle / Ivy
/*
* 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
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* KIND, either express or implied. See the License for the
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*/
/**
* The hllmap package contains a space efficient HLL mapping sketch of keys to approximate unique
* count of identifiers. For example, counting the number of unique users (identifiers) per IP
* address.
*
*
In cases where the number of keys is very large, having an individual HLL sketch per key may
* not be practical. If the distribution of values per key is highly skewed where the vast
* majority of keys have only a few values then this mapping sketch will make sense as it will be
* far more space efficient than dedicating individual HLL sketches per key.
*
*
From our own testing, sketching 100 million IPv4 addresses with such a
* highly skewed distribution of identifiers per IP uses only 1.4GB of memory. This translates to
* an average of about 10 bytes per IP allocated to the equivalent of a full k=1024 HLL sketch
* and provides an RSE of less than 2.5%. Your results will vary depending on the actual
* distribution of identifiers per key.
*
* @see org.apache.datasketches.hllmap.UniqueCountMap
*
* @author Lee Rhodes
* @author Kevin Lang
* @author Alexander Saydakov
*/
package org.apache.datasketches.hllmap;