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node.go
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package bolt
import (
"bytes"
"fmt"
"sort"
"unsafe"
)
// node represents an in-memory, deserialized page.
type node struct {
bucket *Bucket
isLeaf bool
unbalanced bool
spilled bool
key []byte
pgid pgid
parent *node
children nodes
inodes inodes
}
// root returns the top-level node this node is attached to.
func (n *node) root() *node {
if n.parent == nil {
return n
}
return n.parent.root()
}
// 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 {
sz, elsz := pageHeaderSize, n.pageElementSize()
for i := 0; i < len(n.inodes); i++ {
item := &n.inodes[i]
sz += elsz + len(item.key) + len(item.value)
}
return sz
}
// sizeLessThan returns true if the node is less than a given size.
// This is an optimization to avoid calculating a large node when we only need
// to know if it fits inside a certain page size.
func (n *node) sizeLessThan(v int) bool {
sz, elsz := pageHeaderSize, n.pageElementSize()
for i := 0; i < len(n.inodes); i++ {
item := &n.inodes[i]
sz += elsz + len(item.key) + len(item.value)
if sz >= v {
return false
}
}
return true
}
// 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 {
if n.isLeaf {
panic(fmt.Sprintf("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) {
if pgid >= n.bucket.tx.meta.pgid {
panic(fmt.Sprintf("pgid (%d) above high water mark (%d)", pgid, n.bucket.tx.meta.pgid))
} else if len(oldKey) <= 0 {
panic("put: zero-length old key")
} else if len(newKey) <= 0 {
panic("put: zero-length new key")
}
// 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
_assert(len(inode.key) > 0, "put: zero-length inode key")
}
// 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()
}
_assert(len(inode.key) > 0, "read: zero-length inode 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
_assert(len(n.key) > 0, "read: zero-length node 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
}
if len(n.inodes) >= 0xFFFF {
panic(fmt.Sprintf("inode overflow: %d (pgid=%d)", len(n.inodes), p.id))
}
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 {
_assert(len(item.key) > 0, "write: zero-length inode key")
// 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
_assert(elem.pgid != p.id, "write: circular dependency occurred")
}
// If the length of key+value is larger than the max allocation size
// then we need to reallocate the byte array pointer.
//
// See: https://github.com/boltdb/bolt/pull/335
klen, vlen := len(item.key), len(item.value)
if len(b) < klen+vlen {
b = (*[maxAllocSize]byte)(unsafe.Pointer(&b[0]))[:]
}
// Write data for the element to the end of the page.
copy(b[0:], item.key)
b = b[klen:]
copy(b[0:], item.value)
b = b[vlen:]
}
// DEBUG ONLY: n.dump()
}
// split breaks up a node into multiple smaller nodes, if appropriate.
// This should only be called from the spill() function.
func (n *node) split(pageSize int) []*node {
var nodes []*node
node := n
for {
// Split node into two.
a, b := node.splitTwo(pageSize)
nodes = append(nodes, a)
// If we can't split then exit the loop.
if b == nil {
break
}
// Set node to b so it gets split on the next iteration.
node = b
}
return nodes
}
// splitTwo breaks up a node into two smaller nodes, if appropriate.
// This should only be called from the split() function.
func (n *node) splitTwo(pageSize int) (*node, *node) {
// Ignore the split if the page doesn't have at least enough nodes for
// two pages or if the nodes can fit in a single page.
if len(n.inodes) <= (minKeysPerPage*2) || n.sizeLessThan(pageSize) {
return n, nil
}
// Determine the threshold before starting a new node.
var fillPercent = n.bucket.FillPercent
if fillPercent < minFillPercent {
fillPercent = minFillPercent
} else if fillPercent > maxFillPercent {
fillPercent = maxFillPercent
}
threshold := int(float64(pageSize) * fillPercent)
// Determine split position and sizes of the two pages.
splitIndex, _ := n.splitIndex(threshold)
// Split node into two separate nodes.
// If there's no parent then we'll need to create one.
if n.parent == nil {
n.parent = &node{bucket: n.bucket, children: []*node{n}}
}
// Create a new node and add it to the parent.
next := &node{bucket: n.bucket, isLeaf: n.isLeaf, parent: n.parent}
n.parent.children = append(n.parent.children, next)
// Split inodes across two nodes.
next.inodes = n.inodes[splitIndex:]
n.inodes = n.inodes[:splitIndex]
// Update the statistics.
n.bucket.tx.stats.Split++
return n, next
}
// splitIndex finds the position where a page will fill a given threshold.
// It returns the index as well as the size of the first page.
// This is only be called from split().
func (n *node) splitIndex(threshold int) (index, sz int) {
sz = pageHeaderSize
// Loop until we only have the minimum number of keys required for the second page.
for i := 0; i < len(n.inodes)-minKeysPerPage; i++ {
index = i
inode := n.inodes[i]
elsize := n.pageElementSize() + len(inode.key) + len(inode.value)
// If we have at least the minimum number of keys and adding another
// node would put us over the threshold then exit and return.
if i >= minKeysPerPage && sz+elsize > threshold {
break
}
// Add the element size to the total size.
sz += elsize
}
return
}
// spill writes the nodes to dirty pages and splits nodes as it goes.
// Returns an error if dirty pages cannot be allocated.
func (n *node) spill() error {
var tx = n.bucket.tx
if n.spilled {
return nil
}
// Spill child nodes first. Child nodes can materialize sibling nodes in
// the case of split-merge so we cannot use a range loop. We have to check
// the children size on every loop iteration.
sort.Sort(n.children)
for i := 0; i < len(n.children); i++ {
if err := n.children[i].spill(); err != nil {
return err
}
}
// We no longer need the child list because it's only used for spill tracking.
n.children = nil
// Split nodes into appropriate sizes. The first node will always be n.
var nodes = n.split(tx.db.pageSize)
for _, node := range nodes {
// Add node's page to the freelist if it's not new.
if node.pgid > 0 {
tx.db.freelist.free(tx.meta.txid, tx.page(node.pgid))
node.pgid = 0
}
// Allocate contiguous space for the node.
p, err := tx.allocate((node.size() / tx.db.pageSize) + 1)
if err != nil {
return err
}
// Write the node.
if p.id >= tx.meta.pgid {
panic(fmt.Sprintf("pgid (%d) above high water mark (%d)", p.id, tx.meta.pgid))
}
node.pgid = p.id
node.write(p)
node.spilled = true
// Insert into parent inodes.
if node.parent != nil {
var key = node.key
if key == nil {
key = node.inodes[0].key
}
node.parent.put(key, node.inodes[0].key, nil, node.pgid, 0)
node.key = node.inodes[0].key
_assert(len(node.key) > 0, "spill: zero-length node key")
}
// Update the statistics.
tx.stats.Spill++
}
// If the root node split and created a new root then we need to spill that
// as well. We'll clear out the children to make sure it doesn't try to respill.
if n.parent != nil && n.parent.pgid == 0 {
n.children = nil
return n.parent.spill()
}
return nil
}
// 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 root's child up.
child := n.bucket.node(n.inodes[0].pgid, n)
n.isLeaf = child.isLeaf
n.inodes = child.inodes[:]
n.children = child.children
// 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
}
// If node has no keys then just remove it.
if n.numChildren() == 0 {
n.parent.del(n.key)
n.parent.removeChild(n)
delete(n.bucket.nodes, n.pgid)
n.free()
n.parent.rebalance()
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.removeChild(child)
child.parent = n
child.parent.children = append(child.parent.children, child)
}
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
_assert(len(target.key) > 0, "rebalance(1): zero-length node key")
} else {
// Reparent and move node.
if child, ok := n.bucket.nodes[target.inodes[len(target.inodes)-1].pgid]; ok {
child.parent.removeChild(child)
child.parent = n
child.parent.children = append(child.parent.children, child)
}
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
_assert(len(n.key) > 0, "rebalance(2): zero-length node 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.removeChild(child)
child.parent = n
child.parent.children = append(child.parent.children, child)
}
}
// Copy over inodes from target and remove target.
n.inodes = append(n.inodes, target.inodes...)
n.parent.del(target.key)
n.parent.removeChild(target)
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.removeChild(child)
child.parent = target
child.parent.children = append(child.parent.children, child)
}
}
// Copy over inodes to target and remove node.
target.inodes = append(target.inodes, n.inodes...)
n.parent.del(n.key)
n.parent.removeChild(n)
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()
}
// removes a node from the list of in-memory children.
// This does not affect the inodes.
func (n *node) removeChild(target *node) {
for i, child := range n.children {
if child == target {
n.children = append(n.children[:i], n.children[i+1:]...)
return
}
}
}
// 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() {
if n.key != nil {
key := make([]byte, len(n.key))
copy(key, n.key)
n.key = key
_assert(n.pgid == 0 || len(n.key) > 0, "dereference: zero-length node key on existing node")
}
for i := range n.inodes {
inode := &n.inodes[i]
key := make([]byte, len(inode.key))
copy(key, inode.key)
inode.key = key
_assert(len(inode.key) > 0, "dereference: zero-length inode key")
value := make([]byte, len(inode.value))
copy(value, inode.value)
inode.value = value
}
// Recursively dereference children.
for _, child := range n.children {
child.dereference()
}
// Update statistics.
n.bucket.tx.stats.NodeDeref++
}
// 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.meta.txid, n.bucket.tx.page(n.pgid))
n.pgid = 0
}
}
// dump writes the contents of the node to STDERR for debugging purposes.
/*
func (n *node) dump() {
// Write node header.
var typ = "branch"
if n.isLeaf {
typ = "leaf"
}
warnf("[NODE %d {type=%s count=%d}]", n.pgid, typ, len(n.inodes))
// Write out abbreviated version of each item.
for _, item := range n.inodes {
if n.isLeaf {
if item.flags&bucketLeafFlag != 0 {
bucket := (*bucket)(unsafe.Pointer(&item.value[0]))
warnf("+L %08x -> (bucket root=%d)", trunc(item.key, 4), bucket.root)
} else {
warnf("+L %08x -> %08x", trunc(item.key, 4), trunc(item.value, 4))
}
} else {
warnf("+B %08x -> pgid=%d", trunc(item.key, 4), item.pgid)
}
}
warn("")
}
*/
type nodes []*node
func (s nodes) Len() int { return len(s) }
func (s nodes) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s nodes) Less(i, j int) bool { return bytes.Compare(s[i].inodes[0].key, s[j].inodes[0].key) == -1 }
// 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