go-bloom

go-bloom copied to clipboard

go-bloom is a collection of bloom filters for Go, including a standard bloom filter, a counting bloom filter, and a layered bloom filter (for counting occurrences of the same item.) All of them use the 64-bit FNV-1 hash function and an efficient bitset.

A bloom filter is a space-efficient probabilistic data structure that is used to test whether an element is a member of a set. False positives are possible, but false negatives are not; i.e. a query returns either "inside set (may be wrong)" or "definitely not in set". Elements can be added to the set, but not removed (though this can be addressed with a counting filter.)

== Installation

go get github.com/pmylund/go-bloom

== Documentation

go doc github.com/pmylund/go-bloom or http://go.pkgdoc.org/github.com/pmylund/go-bloom

== Usage

import "github.com/pmylund/go-bloom"

// Normal bloom filter

// Create a bloom filter which will contain an expected 100,000 items, and which // allows a false positive rate of 1%. f := bloom.New(100000, 0.01)

// Add an item to the filter f.Add([]byte("foo"))

// Check if an item has been added to the filter (if true, subject to the // false positive chance; if false, then the item definitely has not been // added to the filter.) f.Test([]byte("foo"))

// Counting bloom filter

// Create a counting bloom filter which will contain an expected 100,000 items, // and which allows a false positive rate of 1%. f := bloom.NewCounting(100000, 0.01)

// Add an item to the counting filter f.Add([]byte("foo"))

// Remove an item from the counting filter f.Remove([]byte("foo"))

// Layered bloom filter

// Create a layered bloom filter which will contain an expected 100,000 items, // and which allows a false positive rate of 1%. f := bloom.NewLayered(100000, 0.01)

// Add an item to the layered filter f.Add([]byte("foo"))

// Add an item to the layered filter again f.Add([]byte("foo"))

// Find out how many times an item appears in the layered filter count := f.Test([]byte("foo") count == 2

To use go-bloom in multiple goroutines, use a sync.RWMutex, and surround test calls with RLock()/RUnlock(), and set calls with Lock()/()Unlock.

go-bloom is based on bloom by Will Fitzgerald.