README

BTree implementation for Go

Travis CI Build Status

This package provides an in-memory B-Tree implementation for Go, useful as an ordered, mutable data structure.

The API is based off of the wonderful http://godoc.org/github.com/petar/GoLLRB/llrb, and is meant to allow btree to act as a drop-in replacement for gollrb trees.

See http://godoc.org/github.com/google/btree for documentation.

Expand ▾ Collapse ▴

Documentation

Overview

    Package btree implements in-memory B-Trees of arbitrary degree.

    btree implements an in-memory B-Tree for use as an ordered data structure. It is not meant for persistent storage solutions.

    It has a flatter structure than an equivalent red-black or other binary tree, which in some cases yields better memory usage and/or performance. See some discussion on the matter here:

    http://google-opensource.blogspot.com/2013/01/c-containers-that-save-memory-and-time.html
    

    Note, though, that this project is in no way related to the C++ B-Tree implementation written about there.

    Within this tree, each node contains a slice of items and a (possibly nil) slice of children. For basic numeric values or raw structs, this can cause efficiency differences when compared to equivalent C++ template code that stores values in arrays within the node:

    * Due to the overhead of storing values as interfaces (each
      value needs to be stored as the value itself, then 2 words for the
      interface pointing to that value and its type), resulting in higher
      memory use.
    * Since interfaces can point to values anywhere in memory, values are
      most likely not stored in contiguous blocks, resulting in a higher
      number of cache misses.
    

    These issues don't tend to matter, though, when working with strings or other heap-allocated structures, since C++-equivalent structures also must store pointers and also distribute their values across the heap.

    This implementation is designed to be a drop-in replacement to gollrb.LLRB trees, (http://github.com/petar/gollrb), an excellent and probably the most widely used ordered tree implementation in the Go ecosystem currently. Its functions, therefore, exactly mirror those of llrb.LLRB where possible. Unlike gollrb, though, we currently don't support storing multiple equivalent values.

    Index

    Examples

    Constants

    View Source
    const (
    	DefaultFreeListSize = 32
    )

    Variables

    This section is empty.

    Functions

    This section is empty.

    Types

    type BTree

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

      BTree is an implementation of a B-Tree.

      BTree stores Item instances in an ordered structure, allowing easy insertion, removal, and iteration.

      Write operations are not safe for concurrent mutation by multiple goroutines, but Read operations are.

      Example
      Output:
      
      len:        10
      get3:       3
      get100:     <nil>
      del4:       4
      del100:     <nil>
      replace5:   5
      replace100: <nil>
      min:        0
      delmin:     0
      max:        100
      delmax:     100
      len:        8
      

      func New

      func New(degree int) *BTree

        New creates a new B-Tree with the given degree.

        New(2), for example, will create a 2-3-4 tree (each node contains 1-3 items and 2-4 children).

        func NewWithFreeList

        func NewWithFreeList(degree int, f *FreeList) *BTree

          NewWithFreeList creates a new B-Tree that uses the given node free list.

          func (*BTree) Ascend

          func (t *BTree) Ascend(iterator ItemIterator)

            Ascend calls the iterator for every value in the tree within the range [first, last], until iterator returns false.

            func (*BTree) AscendGreaterOrEqual

            func (t *BTree) AscendGreaterOrEqual(pivot Item, iterator ItemIterator)

              AscendGreaterOrEqual calls the iterator for every value in the tree within the range [pivot, last], until iterator returns false.

              func (*BTree) AscendLessThan

              func (t *BTree) AscendLessThan(pivot Item, iterator ItemIterator)

                AscendLessThan calls the iterator for every value in the tree within the range [first, pivot), until iterator returns false.

                func (*BTree) AscendRange

                func (t *BTree) AscendRange(greaterOrEqual, lessThan Item, iterator ItemIterator)

                  AscendRange calls the iterator for every value in the tree within the range [greaterOrEqual, lessThan), until iterator returns false.

                  func (*BTree) Clear

                  func (t *BTree) Clear(addNodesToFreelist bool)

                    Clear removes all items from the btree. If addNodesToFreelist is true, t's nodes are added to its freelist as part of this call, until the freelist is full. Otherwise, the root node is simply dereferenced and the subtree left to Go's normal GC processes.

                    This can be much faster than calling Delete on all elements, because that requires finding/removing each element in the tree and updating the tree accordingly. It also is somewhat faster than creating a new tree to replace the old one, because nodes from the old tree are reclaimed into the freelist for use by the new one, instead of being lost to the garbage collector.

                    This call takes:

                    O(1): when addNodesToFreelist is false, this is a single operation.
                    O(1): when the freelist is already full, it breaks out immediately
                    O(freelist size):  when the freelist is empty and the nodes are all owned
                        by this tree, nodes are added to the freelist until full.
                    O(tree size):  when all nodes are owned by another tree, all nodes are
                        iterated over looking for nodes to add to the freelist, and due to
                        ownership, none are.
                    

                    func (*BTree) Clone

                    func (t *BTree) Clone() (t2 *BTree)

                      Clone clones the btree, lazily. Clone should not be called concurrently, but the original tree (t) and the new tree (t2) can be used concurrently once the Clone call completes.

                      The internal tree structure of b is marked read-only and shared between t and t2. Writes to both t and t2 use copy-on-write logic, creating new nodes whenever one of b's original nodes would have been modified. Read operations should have no performance degredation. Write operations for both t and t2 will initially experience minor slow-downs caused by additional allocs and copies due to the aforementioned copy-on-write logic, but should converge to the original performance characteristics of the original tree.

                      func (*BTree) Delete

                      func (t *BTree) Delete(item Item) Item

                        Delete removes an item equal to the passed in item from the tree, returning it. If no such item exists, returns nil.

                        func (*BTree) DeleteMax

                        func (t *BTree) DeleteMax() Item

                          DeleteMax removes the largest item in the tree and returns it. If no such item exists, returns nil.

                          func (*BTree) DeleteMin

                          func (t *BTree) DeleteMin() Item

                            DeleteMin removes the smallest item in the tree and returns it. If no such item exists, returns nil.

                            func (*BTree) Descend

                            func (t *BTree) Descend(iterator ItemIterator)

                              Descend calls the iterator for every value in the tree within the range [last, first], until iterator returns false.

                              func (*BTree) DescendGreaterThan

                              func (t *BTree) DescendGreaterThan(pivot Item, iterator ItemIterator)

                                DescendGreaterThan calls the iterator for every value in the tree within the range (pivot, last], until iterator returns false.

                                func (*BTree) DescendLessOrEqual

                                func (t *BTree) DescendLessOrEqual(pivot Item, iterator ItemIterator)

                                  DescendLessOrEqual calls the iterator for every value in the tree within the range [pivot, first], until iterator returns false.

                                  func (*BTree) DescendRange

                                  func (t *BTree) DescendRange(lessOrEqual, greaterThan Item, iterator ItemIterator)

                                    DescendRange calls the iterator for every value in the tree within the range [lessOrEqual, greaterThan), until iterator returns false.

                                    func (*BTree) Get

                                    func (t *BTree) Get(key Item) Item

                                      Get looks for the key item in the tree, returning it. It returns nil if unable to find that item.

                                      func (*BTree) Has

                                      func (t *BTree) Has(key Item) bool

                                        Has returns true if the given key is in the tree.

                                        func (*BTree) Len

                                        func (t *BTree) Len() int

                                          Len returns the number of items currently in the tree.

                                          func (*BTree) Max

                                          func (t *BTree) Max() Item

                                            Max returns the largest item in the tree, or nil if the tree is empty.

                                            func (*BTree) Min

                                            func (t *BTree) Min() Item

                                              Min returns the smallest item in the tree, or nil if the tree is empty.

                                              func (*BTree) ReplaceOrInsert

                                              func (t *BTree) ReplaceOrInsert(item Item) Item

                                                ReplaceOrInsert adds the given item to the tree. If an item in the tree already equals the given one, it is removed from the tree and returned. Otherwise, nil is returned.

                                                nil cannot be added to the tree (will panic).

                                                type FreeList

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

                                                  FreeList represents a free list of btree nodes. By default each BTree has its own FreeList, but multiple BTrees can share the same FreeList. Two Btrees using the same freelist are safe for concurrent write access.

                                                  func NewFreeList

                                                  func NewFreeList(size int) *FreeList

                                                    NewFreeList creates a new free list. size is the maximum size of the returned free list.

                                                    type Int

                                                    type Int int

                                                      Int implements the Item interface for integers.

                                                      func (Int) Less

                                                      func (a Int) Less(b Item) bool

                                                        Less returns true if int(a) < int(b).

                                                        type Item

                                                        type Item interface {
                                                        	// Less tests whether the current item is less than the given argument.
                                                        	//
                                                        	// This must provide a strict weak ordering.
                                                        	// If !a.Less(b) && !b.Less(a), we treat this to mean a == b (i.e. we can only
                                                        	// hold one of either a or b in the tree).
                                                        	Less(than Item) bool
                                                        }

                                                          Item represents a single object in the tree.

                                                          type ItemIterator

                                                          type ItemIterator func(i Item) bool

                                                            ItemIterator allows callers of Ascend* to iterate in-order over portions of the tree. When this function returns false, iteration will stop and the associated Ascend* function will immediately return.

                                                            Source Files