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tree.go
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tree.go
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// _ _
// __ _____ __ ___ ___ __ _| |_ ___
// \ \ /\ / / _ \/ _` \ \ / / |/ _` | __/ _ \
// \ V V / __/ (_| |\ V /| | (_| | || __/
// \_/\_/ \___|\__,_| \_/ |_|\__,_|\__\___|
//
// Copyright © 2016 - 2024 Weaviate B.V. All rights reserved.
//
// CONTACT: hello@weaviate.io
//
package segmentindex
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"math"
"sort"
"github.com/pkg/errors"
)
type Tree struct {
nodes []*Node
}
type Node struct {
Key []byte
Start uint64
End uint64
}
func NewTree(capacity int) Tree {
return Tree{
nodes: make([]*Node, 0, capacity),
}
}
func NewBalanced(nodes []Node) Tree {
t := Tree{nodes: make([]*Node, len(nodes))}
if len(nodes) > 0 {
// sort the slice just once
sort.Slice(nodes, func(a, b int) bool {
return bytes.Compare(nodes[a].Key, nodes[b].Key) < 0
})
t.buildBalanced(nodes, 0, 0, len(nodes)-1)
}
return t
}
func (t *Tree) buildBalanced(nodes []Node, targetPos, leftBound, rightBound int) {
t.grow(targetPos)
if leftBound > rightBound {
return
}
mid := (leftBound + rightBound) / 2
t.nodes[targetPos] = &nodes[mid]
t.buildBalanced(nodes, t.left(targetPos), leftBound, mid-1)
t.buildBalanced(nodes, t.right(targetPos), mid+1, rightBound)
}
func (t *Tree) Insert(key []byte, start, end uint64) {
newNode := Node{
Key: key,
Start: start,
End: end,
}
if len(t.nodes) == 0 {
t.nodes = append(t.nodes, &newNode)
return
}
t.insertAt(0, newNode)
}
func (t *Tree) insertAt(nodeID int, newNode Node) {
if !t.exists(nodeID) {
// we are at the target and can insert now
t.grow(nodeID)
t.nodes[nodeID] = &newNode
return
}
if bytes.Equal(newNode.Key, t.nodes[nodeID].Key) {
// this key already exists, which is an unexpected situation for an index
// key
panic(fmt.Sprintf("duplicate key %s", newNode.Key))
}
if bytes.Compare(newNode.Key, t.nodes[nodeID].Key) < 0 {
t.insertAt(t.left(nodeID), newNode)
} else {
t.insertAt(t.right(nodeID), newNode)
}
}
func (t *Tree) Get(key []byte) ([]byte, uint64, uint64) {
if len(t.nodes) == 0 {
return nil, 0, 0
}
return t.getAt(0, key)
}
func (t *Tree) getAt(nodeID int, key []byte) ([]byte, uint64, uint64) {
if !t.exists(nodeID) {
return nil, 0, 0
}
node := t.nodes[nodeID]
if bytes.Equal(node.Key, key) {
return node.Key, node.Start, node.End
}
if bytes.Compare(key, node.Key) < 0 {
return t.getAt(t.left(nodeID), key)
} else {
return t.getAt(t.right(nodeID), key)
}
}
func (t Tree) left(i int) int {
return 2*i + 1
}
func (t Tree) right(i int) int {
return 2*i + 2
}
func (t *Tree) exists(i int) bool {
if i >= len(t.nodes) {
return false
}
return t.nodes[i] != nil
}
// size calculates the exact size of this node on disk which is helpful to
// figure out the personal offset
func (n *Node) size() int {
if n == nil {
return 0
}
size := 0
size += 4 // uint32 for key length
size += len(n.Key)
size += 8 // uint64 startPos
size += 8 // uint64 endPos
size += 8 // int64 pointer left child
size += 8 // int64 pointer right child
return size
}
func (t *Tree) grow(i int) {
if i < len(t.nodes) {
return
}
oldSize := len(t.nodes)
newSize := oldSize
for newSize <= i {
newSize += oldSize
}
newNodes := make([]*Node, newSize)
copy(newNodes, t.nodes)
for i := range t.nodes {
t.nodes[i] = nil
}
t.nodes = newNodes
}
func (t *Tree) MarshalBinary() ([]byte, error) {
offsets, size := t.calculateDiskOffsets()
buf := bytes.NewBuffer(nil)
for i, node := range t.nodes {
if node == nil {
continue
}
var leftOffset int64
var rightOffset int64
if t.exists(t.left(i)) {
leftOffset = int64(offsets[t.left(i)])
} else {
leftOffset = -1
}
if t.exists(t.right(i)) {
rightOffset = int64(offsets[t.right(i)])
} else {
rightOffset = -1
}
if len(node.Key) > math.MaxUint32 {
return nil, errors.Errorf("max key size is %d", math.MaxUint32)
}
keyLen := uint32(len(node.Key))
if err := binary.Write(buf, binary.LittleEndian, keyLen); err != nil {
return nil, err
}
if _, err := buf.Write(node.Key); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.LittleEndian, node.Start); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.LittleEndian, node.End); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.LittleEndian, leftOffset); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.LittleEndian, rightOffset); err != nil {
return nil, err
}
}
bytes := buf.Bytes()
if size != len(bytes) {
return nil, errors.Errorf("corrupt: wrote %d bytes with target %d", len(bytes), size)
}
return bytes, nil
}
func (t *Tree) MarshalBinaryInto(w io.Writer) (int64, error) {
offsets, size := t.calculateDiskOffsets()
// create buf just once and reuse for each iteration, each iteration
// overwrites every single byte of the buffer, so no initializing or
// resetting after a round is required.
buf := make([]byte, 36) // 1x uint32 + 4x uint64
for i, node := range t.nodes {
if node == nil {
continue
}
var leftOffset int64
var rightOffset int64
if t.exists(t.left(i)) {
leftOffset = int64(offsets[t.left(i)])
} else {
leftOffset = -1
}
if t.exists(t.right(i)) {
rightOffset = int64(offsets[t.right(i)])
} else {
rightOffset = -1
}
if len(node.Key) > math.MaxUint32 {
return 0, errors.Errorf("max key size is %d", math.MaxUint32)
}
keyLen := uint32(len(node.Key))
binary.LittleEndian.PutUint32(buf[0:4], keyLen)
binary.LittleEndian.PutUint64(buf[4:12], node.Start)
binary.LittleEndian.PutUint64(buf[12:20], node.End)
binary.LittleEndian.PutUint64(buf[20:28], uint64(leftOffset))
binary.LittleEndian.PutUint64(buf[28:36], uint64(rightOffset))
if _, err := w.Write(buf[:4]); err != nil {
return 0, err
}
if _, err := w.Write(node.Key); err != nil {
return 0, err
}
if _, err := w.Write(buf[4:36]); err != nil {
return 0, err
}
}
return int64(size), nil
}
// returns individual offsets and total size, nil nodes are skipped
func (t *Tree) calculateDiskOffsets() ([]int, int) {
current := 0
out := make([]int, len(t.nodes))
for i, node := range t.nodes {
out[i] = current
size := node.size()
current += size
}
return out, current
}
func (t *Tree) Height() int {
var highestElem int
for i := len(t.nodes) - 1; i >= 0; i-- {
if t.nodes[i] != nil {
highestElem = i
break
}
}
return int(math.Ceil(math.Log2(float64(highestElem))))
}