package bart

Overview

package bart provides a Balanced-Routing-Table (BART).

BART is balanced in terms of memory usage and lookup time for the longest-prefix match.

The longest-prefix match is on average slower than the ART routing algorithm, but reduces memory usage by more than an order of magnitude.

BART is a multibit-trie with fixed stride length of 8 bits, using the baseIndex function from the ART algorithm to build the complete-binary-tree (CBT) of prefixes for each stride.

example from artlookup.pdf for a 4bit stride

The CBT is implemented as a bitvector, backtracking is just a matter of fast cache friendly bitmask operations.

The prefix and child arrays at each stride level are popcount compressed sparse arrays.

API

The API has changed in ..., v0.10.1, v0.11.0, v0.12.0, v0.12.6, v0.16.0

  import "github.com/gaissmai/bart"
  
  type Table[V any] struct {
  	// Has unexported fields.
  }
    Table is an IPv4 and IPv6 routing table with payload V. The zero value is
    ready to use.

    The Table is safe for concurrent readers but not for concurrent readers
    and/or writers.

  func (t *Table[V]) Insert(pfx netip.Prefix, val V)
  func (t *Table[V]) Update(pfx netip.Prefix, cb func(val V, ok bool) V) (newVal V)
  func (t *Table[V]) Delete(pfx netip.Prefix)

  func (t *Table[V]) Get(pfx netip.Prefix) (val V, ok bool)
  func (t *Table[V]) GetAndDelete(pfx netip.Prefix) (val V, ok bool)

  func (t *Table[V]) Union(o *Table[V])
  func (t *Table[V]) Clone() *Table[V]

  func (t *Table[V]) Contains(ip netip.Addr) bool
  func (t *Table[V]) Lookup(ip netip.Addr) (val V, ok bool)
  func (t *Table[V]) LookupPrefix(pfx netip.Prefix) (val V, ok bool)
  func (t *Table[V]) LookupPrefixLPM(pfx netip.Prefix) (lpm netip.Prefix, val V, ok bool)

  func (t *Table[V]) OverlapsPrefix(pfx netip.Prefix) bool

  func (t *Table[V]) Overlaps(o *Table[V])  bool
  func (t *Table[V]) Overlaps4(o *Table[V]) bool
  func (t *Table[V]) Overlaps6(o *Table[V]) bool

  func (t *Table[V]) Subnets(pfx netip.Prefix)   func(yield func(netip.Prefix, V) bool)
  func (t *Table[V]) Supernets(pfx netip.Prefix) func(yield func(netip.Prefix, V) bool)

  func (t *Table[V]) All()  func(yield func(pfx netip.Prefix, val V) bool)
  func (t *Table[V]) All4() func(yield func(pfx netip.Prefix, val V) bool)
  func (t *Table[V]) All6() func(yield func(pfx netip.Prefix, val V) bool)

  func (t *Table[V]) AllSorted()  func(yield func(pfx netip.Prefix, val V) bool)
  func (t *Table[V]) AllSorted4() func(yield func(pfx netip.Prefix, val V) bool)
  func (t *Table[V]) AllSorted6() func(yield func(pfx netip.Prefix, val V) bool)

  func (t *Table[V]) Size()  int
  func (t *Table[V]) Size4() int
  func (t *Table[V]) Size6() int

  func (t *Table[V]) String() string
  func (t *Table[V]) Fprint(w io.Writer) error
  func (t *Table[V]) MarshalText() ([]byte, error)
  func (t *Table[V]) MarshalJSON() ([]byte, error)

  func (t *Table[V]) DumpList4() []DumpListNode[V]
  func (t *Table[V]) DumpList6() []DumpListNode[V]

benchmarks

Please see the extensive benchmarks comparing bart with other IP routing table implementations.

Just a teaser, LPM lookups against the full Internet routing table with random probes:

$ go test -run=xxx -benchmem -cpu=1 -bench=Full/Contains
goos: linux
goarch: amd64
pkg: github.com/gaissmai/bart
cpu: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
BenchmarkFullMatchV4/Contains         	48157468	        22.14 ns/op	       0 B/op	       0 allocs/op
BenchmarkFullMatchV6/Contains         	34797141	        31.83 ns/op	       0 B/op	       0 allocs/op
BenchmarkFullMissV4/Contains          	46614062	        22.72 ns/op	       0 B/op	       0 allocs/op
BenchmarkFullMissV6/Contains          	61439612	        16.79 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/gaissmai/bart	18.153s

Compatibility Guarantees

The package is currently released as a pre-v1 version, which gives the author the freedom to break backward compatibility to help improve the API as he learns which initial design decisions would need to be revisited to better support the use cases that the library solves for.

These occurrences are expected to be rare in frequency and the API is already quite stable.

CONTRIBUTION

Please open an issue for discussion before sending a pull request.

CREDIT

Standing on the shoulders of giants.

Credits for many inspirations go to

• the clever guys at tailscale,
• to Daniel Lemire, and
• to Donald E. Knuth for the ART routing algorithm and

all the rest of his Art and for keeping important algorithms in the public domain!

And last but not least to the Go team who do a wonderful job!

LICENSE

MIT