com.yahoo.sketches.hllmap.package-info Maven / Gradle / Ivy
/*
* Copyright 2017, Yahoo! Inc. Licensed under the terms of the
* Apache License 2.0. See LICENSE file at the project root for terms.
*/
/**
* 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 com.yahoo.sketches.hllmap.UniqueCountMap
*
* @author Lee Rhodes
* @author Kevin Lang
* @author Alexander Saydakov
*/
package com.yahoo.sketches.hllmap;