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bucket.go
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package bolt
import (
"bytes"
"fmt"
"unsafe"
)
const (
// MaxKeySize is the maximum length of a key, in bytes.
MaxKeySize = 32768
// MaxValueSize is the maximum length of a value, in bytes.
MaxValueSize = (1 << 31) - 2
)
const (
maxUint = ^uint(0)
minUint = 0
maxInt = int(^uint(0) >> 1)
minInt = -maxInt - 1
)
const bucketHeaderSize = int(unsafe.Sizeof(bucket{}))
const (
minFillPercent = 0.1
maxFillPercent = 1.0
)
// DefaultFillPercent is the percentage that split pages are filled.
// This value can be changed by setting Bucket.FillPercent.
const DefaultFillPercent = 0.5
// Bucket represents a collection of key/value pairs inside the database.
type Bucket struct {
*bucket
tx *Tx // the associated transaction
buckets map[string]*Bucket // subbucket cache
page *page // inline page reference
rootNode *node // materialized node for the root page.
nodes map[pgid]*node // node cache
// Sets the threshold for filling nodes when they split. By default,
// the bucket will fill to 50% but it can be useful to increase this
// amount if you know that your write workloads are mostly append-only.
//
// This is non-persisted across transactions so it must be set in every Tx.
FillPercent float64
}
// bucket represents the on-file representation of a bucket.
// This is stored as the "value" of a bucket key. If the bucket is small enough,
// then its root page can be stored inline in the "value", after the bucket
// header. In the case of inline buckets, the "root" will be 0.
type bucket struct {
root pgid // page id of the bucket's root-level page
sequence uint64 // monotonically incrementing, used by NextSequence()
}
// newBucket returns a new bucket associated with a transaction.
func newBucket(tx *Tx) Bucket {
var b = Bucket{tx: tx, FillPercent: DefaultFillPercent}
if tx.writable {
b.buckets = make(map[string]*Bucket)
b.nodes = make(map[pgid]*node)
}
return b
}
// Tx returns the tx of the bucket.
func (b *Bucket) Tx() *Tx {
return b.tx
}
// Root returns the root of the bucket.
func (b *Bucket) Root() pgid {
return b.root
}
// Writable returns whether the bucket is writable.
func (b *Bucket) Writable() bool {
return b.tx.writable
}
// Cursor creates a cursor associated with the bucket.
// The cursor is only valid as long as the transaction is open.
// Do not use a cursor after the transaction is closed.
func (b *Bucket) Cursor() *Cursor {
// Update transaction statistics.
b.tx.stats.CursorCount++
// Allocate and return a cursor.
return &Cursor{
bucket: b,
stack: make([]elemRef, 0),
}
}
// Bucket retrieves a nested bucket by name.
// Returns nil if the bucket does not exist.
// The bucket instance is only valid for the lifetime of the transaction.
func (b *Bucket) Bucket(name []byte) *Bucket {
if b.buckets != nil {
if child := b.buckets[string(name)]; child != nil {
return child
}
}
// Move cursor to key.
c := b.Cursor()
k, v, flags := c.seek(name)
// Return nil if the key doesn't exist or it is not a bucket.
if !bytes.Equal(name, k) || (flags&bucketLeafFlag) == 0 {
return nil
}
// Otherwise create a bucket and cache it.
var child = b.openBucket(v)
if b.buckets != nil {
b.buckets[string(name)] = child
}
return child
}
// Helper method that re-interprets a sub-bucket value
// from a parent into a Bucket
func (b *Bucket) openBucket(value []byte) *Bucket {
var child = newBucket(b.tx)
// If unaligned load/stores are broken on this arch and value is
// unaligned simply clone to an aligned byte array.
unaligned := brokenUnaligned && uintptr(unsafe.Pointer(&value[0]))&3 != 0
if unaligned {
value = cloneBytes(value)
}
// If this is a writable transaction then we need to copy the bucket entry.
// Read-only transactions can point directly at the mmap entry.
if b.tx.writable && !unaligned {
child.bucket = &bucket{}
*child.bucket = *(*bucket)(unsafe.Pointer(&value[0]))
} else {
child.bucket = (*bucket)(unsafe.Pointer(&value[0]))
}
// Save a reference to the inline page if the bucket is inline.
if child.root == 0 {
child.page = (*page)(unsafe.Pointer(&value[bucketHeaderSize]))
}
return &child
}
// CreateBucket creates a new bucket at the given key and returns the new bucket.
// Returns an error if the key already exists, if the bucket name is blank, or if the bucket name is too long.
// The bucket instance is only valid for the lifetime of the transaction.
func (b *Bucket) CreateBucket(key []byte) (*Bucket, error) {
if b.tx.db == nil {
return nil, ErrTxClosed
} else if !b.tx.writable {
return nil, ErrTxNotWritable
} else if len(key) == 0 {
return nil, ErrBucketNameRequired
}
// Move cursor to correct position.
c := b.Cursor()
k, _, flags := c.seek(key)
// Return an error if there is an existing key.
if bytes.Equal(key, k) {
if (flags & bucketLeafFlag) != 0 {
return nil, ErrBucketExists
}
return nil, ErrIncompatibleValue
}
// Create empty, inline bucket.
var bucket = Bucket{
bucket: &bucket{},
rootNode: &node{isLeaf: true},
FillPercent: DefaultFillPercent,
}
var value = bucket.write()
// Insert into node.
key = cloneBytes(key)
c.node().put(key, key, value, 0, bucketLeafFlag)
// Since subbuckets are not allowed on inline buckets, we need to
// dereference the inline page, if it exists. This will cause the bucket
// to be treated as a regular, non-inline bucket for the rest of the tx.
b.page = nil
return b.Bucket(key), nil
}
// CreateBucketIfNotExists creates a new bucket if it doesn't already exist and returns a reference to it.
// Returns an error if the bucket name is blank, or if the bucket name is too long.
// The bucket instance is only valid for the lifetime of the transaction.
func (b *Bucket) CreateBucketIfNotExists(key []byte) (*Bucket, error) {
child, err := b.CreateBucket(key)
if err == ErrBucketExists {
return b.Bucket(key), nil
} else if err != nil {
return nil, err
}
return child, nil
}
// DeleteBucket deletes a bucket at the given key.
// Returns an error if the bucket does not exists, or if the key represents a non-bucket value.
func (b *Bucket) DeleteBucket(key []byte) error {
if b.tx.db == nil {
return ErrTxClosed
} else if !b.Writable() {
return ErrTxNotWritable
}
// Move cursor to correct position.
c := b.Cursor()
k, _, flags := c.seek(key)
// Return an error if bucket doesn't exist or is not a bucket.
if !bytes.Equal(key, k) {
return ErrBucketNotFound
} else if (flags & bucketLeafFlag) == 0 {
return ErrIncompatibleValue
}
// Recursively delete all child buckets.
child := b.Bucket(key)
err := child.ForEach(func(k, v []byte) error {
if v == nil {
if err := child.DeleteBucket(k); err != nil {
return fmt.Errorf("delete bucket: %s", err)
}
}
return nil
})
if err != nil {
return err
}
// Remove cached copy.
delete(b.buckets, string(key))
// Release all bucket pages to freelist.
child.nodes = nil
child.rootNode = nil
child.free()
// Delete the node if we have a matching key.
c.node().del(key)
return nil
}
// Get retrieves the value for a key in the bucket.
// Returns a nil value if the key does not exist or if the key is a nested bucket.
// The returned value is only valid for the life of the transaction.
func (b *Bucket) Get(key []byte) []byte {
k, v, flags := b.Cursor().seek(key)
// Return nil if this is a bucket.
if (flags & bucketLeafFlag) != 0 {
return nil
}
// If our target node isn't the same key as what's passed in then return nil.
if !bytes.Equal(key, k) {
return nil
}
return v
}
// Put sets the value for a key in the bucket.
// If the key exist then its previous value will be overwritten.
// Supplied value must remain valid for the life of the transaction.
// Returns an error if the bucket was created from a read-only transaction, if the key is blank, if the key is too large, or if the value
B422
is too large.
func (b *Bucket) Put(key []byte, value []byte) error {
if b.tx.db == nil {
return ErrTxClosed
} else if !b.Writable() {
return ErrTxNotWritable
} else if len(key) == 0 {
return ErrKeyRequired
} else if len(key) > MaxKeySize {
return ErrKeyTooLarge
} else if int64(len(value)) > MaxValueSize {
return ErrValueTooLarge
}
// Move cursor to correct position.
c := b.Cursor()
k, _, flags := c.seek(key)
// Return an error if there is an existing key with a bucket value.
if bytes.Equal(key, k) && (flags&bucketLeafFlag) != 0 {
return ErrIncompatibleValue
}
// Insert into node.
key = cloneBytes(key)
c.node().put(key, key, value, 0, 0)
return nil
}
// Delete removes a key from the bucket.
// If the key does not exist then nothing is done and a nil error is returned.
// Returns an error if the bucket was created from a read-only transaction.
func (b *Bucket) Delete(key []byte) error {
if b.tx.db == nil {
return ErrTxClosed
} else if !b.Writable() {
return ErrTxNotWritable
}
// Move cursor to correct position.
c := b.Cursor()
_, _, flags := c.seek(key)
// Return an error if there is already existing bucket value.
if (flags & bucketLeafFlag) != 0 {
return ErrIncompatibleValue
}
// Delete the node if we have a matching key.
c.node().del(key)
return nil
}
// Sequence returns the current integer for the bucket without incrementing it.
func (b *Bucket) Sequence() uint64 { return b.bucket.sequence }
// SetSequence updates the sequence number for the bucket.
func (b *Bucket) SetSequence(v uint64) error {
if b.tx.db == nil {
return ErrTxClosed
} else if !b.Writable() {
return ErrTxNotWritable
}
// Materialize the root node if it hasn't been already so that the
// bucket will be saved during commit.
if b.rootNode == nil {
_ = b.node(b.root, nil)
}
// Increment and return the sequence.
b.bucket.sequence = v
return nil
}
// NextSequence returns an autoincrementing integer for the bucket.
func (b *Bucket) NextSequence() (uint64, error) {
if b.tx.db == nil {
return 0, ErrTxClosed
} else if !b.Writable() {
return 0, ErrTxNotWritable
}
// Materialize the root node if it hasn't been already so that the
// bucket will be saved during commit.
if b.rootNode == nil {
_ = b.node(b.root, nil)
}
// Increment and return the sequence.
b.bucket.sequence++
return b.bucket.sequence, nil
}
// ForEach executes a function for each key/value pair in a bucket.
// If the provided function returns an error then the iteration is stopped and
// the error is returned to the caller. The provided function must not modify
// the bucket; this will result in undefined behavior.
func (b *Bucket) ForEach(fn func(k, v []byte) error) error {
if b.tx.db == nil {
return ErrTxClosed
}
c := b.Cursor()
for k, v := c.First(); k != nil; k, v = c.Next() {
if err := fn(k, v); err != nil {
return err
}
}
return nil
}
// Stat returns stats on a bucket.
func (b *Bucket) Stats() BucketStats {
var s, subStats BucketStats
pageSize := b.tx.db.pageSize
s.BucketN += 1
if b.root == 0 {
s.InlineBucketN += 1
}
b.forEachPage(func(p *page, depth int) {
if (p.flags & leafPageFlag) != 0 {
s.KeyN += int(p.count)
// used totals the used bytes for the page
used := pageHeaderSize
if p.count != 0 {
// If page has any elements, add all element headers.
used += leafPageElementSize * int(p.count-1)
// Add all element key, value sizes.
// The computation takes advantage of the fact that the position
// of the last element's key/value equals to the total of the sizes
// of all previous elements' keys and values.
// It also includes the last element's header.
lastElement := p.leafPageElement(p.count - 1)
used += int(lastElement.pos + lastElement.ksize + lastElement.vsize)
}
if b.root == 0 {
// For inlined bucket just update the inline stats
s.InlineBucketInuse += used
} else {
// For non-inlined bucket update all the leaf stats
s.LeafPageN++
s.LeafInuse += used
s.LeafOverflowN += int(p.overflow)
// Collect stats from sub-buckets.
// Do that by iterating over all element headers
// looking for the ones with the bucketLeafFlag.
for i := uint16(0); i < p.count; i++ {
e := p.leafPageElement(i)
if (e.flags & bucketLeafFlag) != 0 {
// For any bucket element, open the element value
// and recursively call Stats on the contained bucket.
subStats.Add(b.openBucket(e.value()).Stats())
}
}
}
} else if (p.flags & branchPageFlag) != 0 {
s.BranchPageN++
lastElement := p.branchPageElement(p.count - 1)
// used totals the used bytes for the page
// Add header and all element headers.
used := pageHeaderSize + (branchPageElementSize * int(p.count-1))
// Add size of all keys and values.
// Again, use the fact that last element's position equals to
// the total of key, value sizes of all previous elements.
used += int(lastElement.pos + lastElement.ksize)
s.BranchInuse += used
s.BranchOverflowN += int(p.overflow)
}
// Keep track of maximum page depth.
if depth+1 > s.Depth {
s.Depth = (depth + 1)
}
})
// Alloc stats can be computed from page counts and pageSize.
s.BranchAlloc = (s.BranchPageN + s.BranchOverflowN) * pageSize
s.LeafAlloc = (s.LeafPageN + s.LeafOverflowN) * pageSize
// Add the max depth of sub-buckets to get total nested depth.
s.Depth += subStats.Depth
// Add the stats for all sub-buckets
s.Add(subStats)
return s
}
// forEachPage iterates over every page in a bucket, including inline pages.
func (b *Bucket) forEachPage(fn func(*page, int)) {
// If we have an inline page then just use that.
if b.page != nil {
fn(b.page, 0)
return
}
// Otherwise traverse the page hierarchy.
b.tx.forEachPage(b.root, 0, fn)
}
// forEachPageNode iterates over every page (or node) in a bucket.
// This also includes inline pages.
func (b *Bucket) forEachPageNode(fn func(*page, *node, int)) {
// If we have an inline page or root node then just use that.
if b.page != nil {
fn(b.page, nil, 0)
return
}
b._forEachPageNode(b.root, 0, fn)
}
func (b *Bucket) _forEachPageNode(pgid pgid, depth int, fn func(*page, *node, int)) {
var p, n = b.pageNode(pgid)
// Execute function.
fn(p, n, depth)
// Recursively loop over children.
if p != nil {
if (p.flags & branchPageFlag) != 0 {
for i := 0; i < int(p.count); i++ {
elem := p.branchPageElement(uint16(i))
b._forEachPageNode(elem.pgid, depth+1, fn)
}
}
} else {
if !n.isLeaf {
for _, inode := range n.inodes {
b._forEachPageNode(inode.pgid, depth+1, fn)
}
}
}
}
// spill writes all the nodes for this bucket to dirty pages.
func (b *Bucket) spill() error {
// Spill all child buckets first.
for name, child := range b.buckets {
// If the child bucket is small enough and it has no child buckets then
// write it inline into the parent bucket's page. Otherwise spill it
// like a normal bucket and make the parent value a pointer to the page.
var value []byte
if child.inlineable() {
child.free()
value = child.write()
} else {
if err := child.spill(); err != nil {
return err
}
// Update the child bucket header in this bucket.
value = make([]byte, unsafe.Sizeof(bucket{}))
var bucket = (*bucket)(unsafe.Pointer(&value[0]))
*bucket = *child.bucket
}
// Skip writing the bucket if there are no materialized nodes.
if child.rootNode == nil {
continue
}
// Update parent node.
var c = b.Cursor()
k, _, flags := c.seek([]byte(name))
if !bytes.Equal([]byte(name), k) {
panic(fmt.Sprintf("misplaced bucket header: %x -> %x", []byte(name), k))
}
if flags&bucketLeafFlag == 0 {
panic(fmt.Sprintf("unexpected bucket header flag: %x", flags))
}
c.node().put([]byte(name), []byte(name), value, 0, bucketLeafFlag)
}
// Ignore if there's not a materialized root node.
if b.rootNode == nil {
return nil
}
// Spill nodes.
if err := b.rootNode.spill(); err != nil {
return err
}
b.rootNode = b.rootNode.root()
// Update the root node for this bucket.
if b.rootNode.pgid >= b.tx.meta.pgid {
panic(fmt.Sprintf("pgid (%d) above high water mark (%d)", b.rootNode.pgid, b.tx.meta.pgid))
}
b.root = b.rootNode.pgid
return nil
}
// inlineable returns true if a bucket is small enough to be written inline
// and if it contains no subbuckets. Otherwise returns false.
func (b *Bucket) inlineable() bool {
var n = b.rootNode
// Bucket must only contain a single leaf node.
if n == nil || !n.isLeaf {
return false
}
// Bucket is not inlineable if it contains subbuckets or if it goes beyond
// our threshold for inline bucket size.
var size = pageHeaderSize
for _, inode := range n.inodes {
size += leafPageElementSize + len(inode.key) + len(inode.value)
if inode.flags&bucketLeafFlag != 0 {
return false
} else if size > b.maxInlineBucketSize() {
return false
}
}
return true
}
// Returns the maximum total size of a bucket to make it a candidate for inlining.
func (b *Bucket) maxInlineBucketSize() int {
return b.tx.db.pageSize / 4
}
// write allocates and writes a bucket to a byte slice.
func (b *Bucket) write() []byte {
// Allocate the appropriate size.
var n = b.rootNode
var value = make([]byte, bucketHeaderSize+n.size())
// Write a bucket header.
var bucket = (*bucket)(unsafe.Pointer(&value[0]))
*bucket = *b.bucket
// Convert byte slice to a fake page and write the root node.
var p = (*page)(unsafe.Pointer(&value[bucketHeaderSize]))
n.write(p)
return value
}
// rebalance attempts to balance all nodes.
func (b *Bucket) rebalance() {
for _, n := range b.nodes {
n.rebalance()
}
for _, child := range b.buckets {
child.rebalance()
}
}
// node creates a node from a page and associates it with a given parent.
func (b *Bucket) node(pgid pgid, parent *node) *node {
_assert(b.nodes != nil, "nodes map expected")
// Retrieve node if it's already been created.
if n := b.nodes[pgid]; n != nil {
return n
}
// Otherwise create a node and cache it.
n := &node{bucket: b, parent: parent}
if parent == nil {
b.rootNode = n
} else {
parent.children = append(parent.children, n)
}
// Use the inline page if this is an inline bucket.
var p = b.page
if p == nil {
p = b.tx.page(pgid)
}
// Read the page into the node and cache it.
n.read(p)
b.nodes[pgid] = n
// Update statistics.
b.tx.stats.NodeCount++
return n
}
// free recursively frees all pages in the bucket.
func (b *Bucket) free() {
if b.root == 0 {
return
}
var tx = b.tx
b.forEachPageNode(func(p *page, n *node, _ int) {
if p != nil {
tx.db.freelist.free(tx.meta.txid, p)
} else {
n.free()
}
})
b.root = 0
}
// dereference removes all references to the old mmap.
func (b *Bucket) dereference() {
if b.rootNode != nil {
b.rootNode.root().dereference()
}
for _, child := range b.buckets {
child.dereference()
}
}
// pageNode returns the in-memory node, if it exists.
// Otherwise returns the underlying page.
func (b *Bucket) pageNode(id pgid) (*page, *node) {
// Inline buckets have a fake page embedded in their value so treat them
// differently. We'll return the rootNode (if available) or the fake page.
if b.root == 0 {
if id != 0 {
panic(fmt.Sprintf("inline bucket non-zero page access(2): %d != 0", id))
}
if b.rootNode != nil {
return nil, b.rootNode
}
return b.page, nil
}
// Check the node cache for non-inline buckets.
if b.nodes != nil {
if n := b.nodes[id]; n != nil {
return nil, n
}
}
// Finally lookup the page from the transaction if no node is materialized.
return b.tx.page(id), nil
}
// BucketStats records statistics about resources used by a bucket.
type BucketStats struct {
// Page count statistics.
BranchPageN int // number of logical branch pages
BranchOverflowN int // number of physical branch overflow pages
LeafPageN int // number of logical leaf pages
LeafOverflowN int // number of physical leaf overflow pages
// Tree statistics.
KeyN int // number of keys/value pairs
Depth int // number of levels in B+tree
// Page size utilization.
BranchAlloc int // bytes allocated for physical branch pages
BranchInuse int // bytes actually used for branch data
LeafAlloc int // bytes allocated for physical leaf pages
LeafInuse int // bytes actually used for leaf data
// Bucket statistics
BucketN int // total number of buckets including the top bucket
InlineBucketN int // total number on inlined buckets
InlineBucketInuse int // bytes used for inlined buckets (also accounted for in LeafInuse)
}
func (s *BucketStats) Add(other BucketStats) {
s.BranchPageN += other.BranchPageN
s.BranchOverflowN += other.BranchOverflowN
s.LeafPageN += other.LeafPageN
s.LeafOverflowN += other.LeafOverflowN
s.KeyN += other.KeyN
if s.Depth < other.Depth {
s.Depth = other.Depth
}
s.BranchAlloc += other.BranchAlloc
s.BranchInuse += other.BranchInuse
s.LeafAlloc += other.LeafAlloc
s.LeafInuse += other.LeafInuse
s.BucketN += other.BucketN
s.InlineBucketN += other.InlineBucketN
s.InlineBucketInuse += other.InlineBucketInuse
}
// cloneBytes returns a copy of a given slice.
func cloneBytes(v []byte) []byte {
var clone = make([]byte, len(v))
copy(clone, v)
return clone
}