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Boolean, counting and layered bloom filters for Go
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LICENSE
README
bloom.go
bloom64.go
bloom64_test.go
bloom_test.go

README

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.
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