b

Documentation

Overview

Package b implements a B+tree.

Changelog

2014-06-26: Lower GC presure by recycling things.

2014-04-18: Added new method Put.

Generic types

Keys and their associated values are interface{} typed, similar to all of the containers in the standard library.

Semiautomatic production of a type specific variant of this package is supported via

$ make generic

This command will write to stdout a version of the btree.go file where every key type occurrence is replaced by the word 'key' (written in all CAPS) and every value type occurrence is replaced by the word 'value' (written in all CAPS). Then you have to replace these tokens with your desired type(s), using any technique you're comfortable with.

This is how, for example, 'example/int.go' was created:

$ mkdir example
$
$ # Note: the command bellow must be actually written using the words
$ # 'key' and 'value' in all CAPS. The proper form is avoided in this
$ # documentation to not confuse any text replacement mechanism.
$
$ make generic | sed -e 's/key/int/g' -e 's/value/int/g' > example/int.go

No other changes to int.go are necessary, it compiles just fine.

Running the benchmarks for 1000 keys on a machine with Intel i5-4670 CPU @ 3.4GHz, Go release 1.3.

$ go test -bench 1e3 example/all_test.go example/int.go
PASS
BenchmarkSetSeq1e3	   10000	    146740 ns/op
BenchmarkGetSeq1e3	   10000	    108261 ns/op
BenchmarkSetRnd1e3	   10000	    254359 ns/op
BenchmarkGetRnd1e3	   10000	    134621 ns/op
BenchmarkDelRnd1e3	   10000	    211864 ns/op
BenchmarkSeekSeq1e3	   10000	    148628 ns/op
BenchmarkSeekRnd1e3	   10000	    215166 ns/op
BenchmarkNext1e3	  200000	      9211 ns/op
BenchmarkPrev1e3	  200000	      8843 ns/op
ok  	command-line-arguments	25.071s
$

Index

• type Cmp
• type Enumerator
  • func (e *Enumerator) Close()
  • func (e *Enumerator) Next() (k int64, v struct{}, err error)
  • func (e *Enumerator) Prev() (k int64, v struct{}, err error)
• type Tree
  • func TreeNew(cmp Cmp) *Tree
  • func (t *Tree) Clear()
  • func (t *Tree) Close()
  • func (t *Tree) Delete(k int64) (ok bool)
  • func (t *Tree) First() (k int64, v struct{})
  • func (t *Tree) Get(k int64) (v struct{}, ok bool)
  • func (t *Tree) Last() (k int64, v struct{})
  • func (t *Tree) Len() int
  • func (t *Tree) Put(k int64, upd func(oldV struct{}, exists bool) (newV struct{}, write bool)) (oldV struct{}, written bool)
  • func (t *Tree) Seek(k int64) (e *Enumerator, ok bool)
  • func (t *Tree) SeekFirst() (e *Enumerator, err error)
  • func (t *Tree) SeekLast() (e *Enumerator, err error)
  • func (t *Tree) Set(k int64, v struct{})

Types

type Cmp

type Cmp func(a, b int64) int

Cmp compares a and b. Return value is:

< 0 if a <  b
  0 if a == b
> 0 if a >  b

type Enumerator

type Enumerator struct {
	// contains filtered or unexported fields
}

Enumerator captures the state of enumerating a tree. It is returned from the Seek* methods. The enumerator is aware of any mutations made to the tree in the process of enumerating it and automatically resumes the enumeration at the proper key, if possible.

However, once an Enumerator returns io.EOF to signal "no more items", it does no more attempt to "resync" on tree mutation(s). In other words, io.EOF from an Enumaretor is "sticky" (idempotent).

func (*Enumerator) Close

func (e *Enumerator) Close()

Close recycles e to a pool for possible later reuse. No references to e should exist or such references must not be used afterwards.

func (*Enumerator) Next

func (e *Enumerator) Next() (k int64, v struct{}, err error)

Next returns the currently enumerated item, if it exists and moves to the next item in the key collation order. If there is no item to return, err == io.EOF is returned.

func (*Enumerator) Prev

func (e *Enumerator) Prev() (k int64, v struct{}, err error)

Prev returns the currently enumerated item, if it exists and moves to the previous item in the key collation order. If there is no item to return, err == io.EOF is returned.

type Tree

type Tree struct {
	// contains filtered or unexported fields
}

Tree is a B+tree.

func TreeNew

func TreeNew(cmp Cmp) *Tree

TreeNew returns a newly created, empty Tree. The compare function is used for key collation.

func (*Tree) Clear

func (t *Tree) Clear()

Clear removes all K/V pairs from the tree.

func (*Tree) Close

func (t *Tree) Close()

Close performs Clear and recycles t to a pool for possible later reuse. No references to t should exist or such references must not be used afterwards.

func (*Tree) Delete

func (t *Tree) Delete(k int64) (ok bool)

Delete removes the k's KV pair, if it exists, in which case Delete returns true.

func (*Tree) First

func (t *Tree) First() (k int64, v struct{})

First returns the first item of the tree in the key collating order, or (zero-value, zero-value) if the tree is empty.

func (*Tree) Get

func (t *Tree) Get(k int64) (v struct{}, ok bool)

Get returns the value associated with k and true if it exists. Otherwise Get returns (zero-value, false).

func (*Tree) Last

func (t *Tree) Last() (k int64, v struct{})

Last returns the last item of the tree in the key collating order, or (zero-value, zero-value) if the tree is empty.

func (*Tree) Len

func (t *Tree) Len() int

Len returns the number of items in the tree.

func (*Tree) Put

func (t *Tree) Put(k int64, upd func(oldV struct{}, exists bool) (newV struct{}, write bool)) (oldV struct{}, written bool)

Put combines Get and Set in a more efficient way where the tree is walked only once. The upd(ater) receives (old-value, true) if a KV pair for k exists or (zero-value, false) otherwise. It can then return a (new-value, true) to create or overwrite the existing value in the KV pair, or (whatever, false) if it decides not to create or not to update the value of the KV pair.

tree.Set(k, v) call conceptually equals calling

tree.Put(k, func(int64, bool){ return v, true })

modulo the differing return values.

func (*Tree) Seek

func (t *Tree) Seek(k int64) (e *Enumerator, ok bool)

Seek returns an Enumerator positioned on a an item such that k >= item's key. ok reports if k == item.key The Enumerator's position is possibly after the last item in the tree.

func (*Tree) SeekFirst

func (t *Tree) SeekFirst() (e *Enumerator, err error)

SeekFirst returns an enumerator positioned on the first KV pair in the tree, if any. For an empty tree, err == io.EOF is returned and e will be nil.

func (*Tree) SeekLast

func (t *Tree) SeekLast() (e *Enumerator, err error)

SeekLast returns an enumerator positioned on the last KV pair in the tree, if any. For an empty tree, err == io.EOF is returned and e will be nil.

func (*Tree) Set

func (t *Tree) Set(k int64, v struct{})

Set sets the value associated with k.