bolt/node.go

386 lines
10 KiB
Go

package bolt
import (
"bytes"
"sort"
"unsafe"
)
// node represents an in-memory, deserialized page.
type node struct {
bucket *Bucket
isLeaf bool
unbalanced bool
key []byte
depth int
pgid pgid
parent *node
inodes inodes
}
// minKeys returns the minimum number of inodes this node should have.
func (n *node) minKeys() int {
if n.isLeaf {
return 1
}
return 2
}
// size returns the size of the node after serialization.
func (n *node) size() int {
var elementSize = n.pageElementSize()
var size = pageHeaderSize
for _, item := range n.inodes {
size += elementSize + len(item.key) + len(item.value)
}
return size
}
// pageElementSize returns the size of each page element based on the type of node.
func (n *node) pageElementSize() int {
if n.isLeaf {
return leafPageElementSize
}
return branchPageElementSize
}
// childAt returns the child node at a given index.
func (n *node) childAt(index int) *node {
_assert(!n.isLeaf, "invalid childAt(%d) on a leaf node", index)
return n.bucket.node(n.inodes[index].pgid, n)
}
// childIndex returns the index of a given child node.
func (n *node) childIndex(child *node) int {
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, child.key) != -1 })
return index
}
// numChildren returns the number of children.
func (n *node) numChildren() int {
return len(n.inodes)
}
// nextSibling returns the next node with the same parent.
func (n *node) nextSibling() *node {
if n.parent == nil {
return nil
}
index := n.parent.childIndex(n)
if index >= n.parent.numChildren()-1 {
return nil
}
return n.parent.childAt(index + 1)
}
// prevSibling returns the previous node with the same parent.
func (n *node) prevSibling() *node {
if n.parent == nil {
return nil
}
index := n.parent.childIndex(n)
if index == 0 {
return nil
}
return n.parent.childAt(index - 1)
}
// put inserts a key/value.
func (n *node) put(oldKey, newKey, value []byte, pgid pgid, flags uint32) {
// Find insertion index.
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, oldKey) != -1 })
// Add capacity and shift nodes if we don't have an exact match and need to insert.
exact := (len(n.inodes) > 0 && index < len(n.inodes) && bytes.Equal(n.inodes[index].key, oldKey))
if !exact {
n.inodes = append(n.inodes, inode{})
copy(n.inodes[index+1:], n.inodes[index:])
}
inode := &n.inodes[index]
inode.flags = flags
inode.key = newKey
inode.value = value
inode.pgid = pgid
}
// del removes a key from the node.
func (n *node) del(key []byte) {
// Find index of key.
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, key) != -1 })
// Exit if the key isn't found.
if index >= len(n.inodes) || !bytes.Equal(n.inodes[index].key, key) {
return
}
// Delete inode from the node.
n.inodes = append(n.inodes[:index], n.inodes[index+1:]...)
// Mark the node as needing rebalancing.
n.unbalanced = true
}
// read initializes the node from a page.
func (n *node) read(p *page) {
n.pgid = p.id
n.isLeaf = ((p.flags & leafPageFlag) != 0)
n.inodes = make(inodes, int(p.count))
for i := 0; i < int(p.count); i++ {
inode := &n.inodes[i]
if n.isLeaf {
elem := p.leafPageElement(uint16(i))
inode.flags = elem.flags
inode.key = elem.key()
inode.value = elem.value()
} else {
elem := p.branchPageElement(uint16(i))
inode.pgid = elem.pgid
inode.key = elem.key()
}
}
// Save first key so we can find the node in the parent when we spill.
if len(n.inodes) > 0 {
n.key = n.inodes[0].key
} else {
n.key = nil
}
}
// write writes the items onto one or more pages.
func (n *node) write(p *page) {
// Initialize page.
if n.isLeaf {
p.flags |= leafPageFlag
} else {
p.flags |= branchPageFlag
}
p.count = uint16(len(n.inodes))
// Loop over each item and write it to the page.
b := (*[maxAllocSize]byte)(unsafe.Pointer(&p.ptr))[n.pageElementSize()*len(n.inodes):]
for i, item := range n.inodes {
// Write the page element.
if n.isLeaf {
elem := p.leafPageElement(uint16(i))
elem.pos = uint32(uintptr(unsafe.Pointer(&b[0])) - uintptr(unsafe.Pointer(elem)))
elem.flags = item.flags
elem.ksize = uint32(len(item.key))
elem.vsize = uint32(len(item.value))
} else {
elem := p.branchPageElement(uint16(i))
elem.pos = uint32(uintptr(unsafe.Pointer(&b[0])) - uintptr(unsafe.Pointer(elem)))
elem.ksize = uint32(len(item.key))
elem.pgid = item.pgid
}
// Write data for the element to the end of the page.
copy(b[0:], item.key)
b = b[len(item.key):]
copy(b[0:], item.value)
b = b[len(item.value):]
}
}
// split divides up the node into appropriately sized nodes.
func (n *node) split(pageSize int) []*node {
// Ignore the split if the page doesn't have at least enough nodes for
// multiple pages or if the data can fit on a single page.
if len(n.inodes) <= (minKeysPerPage*2) || n.size() < pageSize {
return []*node{n}
}
// Set fill threshold to 50%.
threshold := pageSize / 2
// Group into smaller pages and target a given fill size.
size := pageHeaderSize
inodes := n.inodes
current := n
current.inodes = nil
var nodes []*node
for i, inode := range inodes {
elemSize := n.pageElementSize() + len(inode.key) + len(inode.value)
if len(current.inodes) >= minKeysPerPage && i < len(inodes)-minKeysPerPage && size+elemSize > threshold {
size = pageHeaderSize
nodes = append(nodes, current)
current = &node{bucket: n.bucket, isLeaf: n.isLeaf}
}
size += elemSize
current.inodes = append(current.inodes, inode)
}
nodes = append(nodes, current)
return nodes
}
// rebalance attempts to combine the node with sibling nodes if the node fill
// size is below a threshold or if there are not enough keys.
func (n *node) rebalance() {
if !n.unbalanced {
return
}
n.unbalanced = false
// Update statistics.
n.bucket.tx.stats.Rebalance++
// Ignore if node is above threshold (25%) and has enough keys.
var threshold = n.bucket.tx.db.pageSize / 4
if n.size() > threshold && len(n.inodes) > n.minKeys() {
return
}
// Root node has special handling.
if n.parent == nil {
// If root node is a branch and only has one node then collapse it.
if !n.isLeaf && len(n.inodes) == 1 {
// Move child's children up.
child := n.bucket.nodes[n.inodes[0].pgid]
n.isLeaf = child.isLeaf
n.inodes = child.inodes[:]
// Reparent all child nodes being moved.
for _, inode := range n.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent = n
}
}
// Remove old child.
child.parent = nil
delete(n.bucket.nodes, child.pgid)
child.free()
}
return
}
_assert(n.parent.numChildren() > 1, "parent must have at least 2 children")
// Destination node is right sibling if idx == 0, otherwise left sibling.
var target *node
var useNextSibling = (n.parent.childIndex(n) == 0)
if useNextSibling {
target = n.nextSibling()
} else {
target = n.prevSibling()
}
// If target node has extra nodes then just move one over.
if target.numChildren() > target.minKeys() {
if useNextSibling {
// Reparent and move node.
if child, ok := n.bucket.nodes[target.inodes[0].pgid]; ok {
child.parent = n
}
n.inodes = append(n.inodes, target.inodes[0])
target.inodes = target.inodes[1:]
// Update target key on parent.
target.parent.put(target.key, target.inodes[0].key, nil, target.pgid, 0)
target.key = target.inodes[0].key
} else {
// Reparent and move node.
if child, ok := n.bucket.nodes[target.inodes[len(target.inodes)-1].pgid]; ok {
child.parent = n
}
n.inodes = append(n.inodes, inode{})
copy(n.inodes[1:], n.inodes)
n.inodes[0] = target.inodes[len(target.inodes)-1]
target.inodes = target.inodes[:len(target.inodes)-1]
}
// Update parent key for node.
n.parent.put(n.key, n.inodes[0].key, nil, n.pgid, 0)
n.key = n.inodes[0].key
return
}
// If both this node and the target node are too small then merge them.
if useNextSibling {
// Reparent all child nodes being moved.
for _, inode := range target.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent = n
}
}
// Copy over inodes from target and remove target.
n.inodes = append(n.inodes, target.inodes...)
n.parent.del(target.key)
delete(n.bucket.nodes, target.pgid)
target.free()
} else {
// Reparent all child nodes being moved.
for _, inode := range n.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent = target
}
}
// Copy over inodes to target and remove node.
target.inodes = append(target.inodes, n.inodes...)
n.parent.del(n.key)
n.parent.put(target.key, target.inodes[0].key, nil, target.pgid, 0)
delete(n.bucket.nodes, n.pgid)
n.free()
}
// Either this node or the target node was deleted from the parent so rebalance it.
n.parent.rebalance()
}
// dereference causes the node to copy all its inode key/value references to heap memory.
// This is required when the mmap is reallocated so inodes are not pointing to stale data.
func (n *node) dereference() {
key := make([]byte, len(n.key))
copy(key, n.key)
n.key = key
for i := range n.inodes {
inode := &n.inodes[i]
key := make([]byte, len(inode.key))
copy(key, inode.key)
inode.key = key
value := make([]byte, len(inode.value))
copy(value, inode.value)
inode.value = value
}
}
// free adds the node's underlying page to the freelist.
func (n *node) free() {
if n.pgid != 0 {
n.bucket.tx.db.freelist.free(n.bucket.tx.id(), n.bucket.tx.page(n.pgid))
}
}
// nodesByDepth sorts a list of branches by deepest first.
type nodesByDepth []*node
func (s nodesByDepth) Len() int { return len(s) }
func (s nodesByDepth) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s nodesByDepth) Less(i, j int) bool { return s[i].depth > s[j].depth }
// inode represents an internal node inside of a node.
// It can be used to point to elements in a page or point
// to an element which hasn't been added to a page yet.
type inode struct {
flags uint32
pgid pgid
key []byte
value []byte
}
type inodes []inode