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// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Package memdb provides in-memory key/value database implementation.
package memdb
import (
"math/rand"
"sync"
"github.com/syndtr/goleveldb/leveldb/comparer"
"github.com/syndtr/goleveldb/leveldb/errors"
"github.com/syndtr/goleveldb/leveldb/iterator"
"github.com/syndtr/goleveldb/leveldb/util"
)
// Common errors.
var (
ErrNotFound = errors.ErrNotFound
ErrIterReleased = errors.New("leveldb/memdb: iterator released")
)
const tMaxHeight = 12
type dbIter struct {
util.BasicReleaser
p *DB
slice *util.Range
node int
forward bool
key, value []byte
err error
}
func (i *dbIter) fill(checkStart, checkLimit bool) bool {
if i.node != 0 {
n := i.p.nodeData[i.node]
m := n + i.p.nodeData[i.node+nKey]
i.key = i.p.kvData[n:m]
if i.slice != nil {
switch {
case checkLimit && i.slice.Limit != nil && i.p.cmp.Compare(i.key, i.slice.Limit) >= 0:
fallthrough
case checkStart && i.slice.Start != nil && i.p.cmp.Compare(i.key, i.slice.Start) < 0:
i.node = 0
goto bail
}
}
i.value = i.p.kvData[m : m+i.p.nodeData[i.node+nVal]]
return true
}
bail:
i.key = nil
i.value = nil
return false
}
func (i *dbIter) Valid() bool {
return i.node != 0
}
func (i *dbIter) First() bool {
if i.Released() {
i.err = ErrIterReleased
return false
}
i.forward = true
i.p.mu.RLock()
defer i.p.mu.RUnlock()
if i.slice != nil && i.slice.Start != nil {
i.node, _ = i.p.findGE(i.slice.Start, false)
} else {
i.node = i.p.nodeData[nNext]
}
return i.fill(false, true)
}
func (i *dbIter) Last() bool {
if i.Released() {
i.err = ErrIterReleased
return false
}
i.forward = false
i.p.mu.RLock()
defer i.p.mu.RUnlock()
if i.slice != nil && i.slice.Limit != nil {
i.node = i.p.findLT(i.slice.Limit)
} else {
i.node = i.p.findLast()
}
return i.fill(true, false)
}
func (i *dbIter) Seek(key []byte) bool {
if i.Released() {
i.err = ErrIterReleased
return false
}
i.forward = true
i.p.mu.RLock()
defer i.p.mu.RUnlock()
if i.slice != nil && i.slice.Start != nil && i.p.cmp.Compare(key, i.slice.Start) < 0 {
key = i.slice.Start
}
i.node, _ = i.p.findGE(key, false)
return i.fill(false, true)
}
func (i *dbIter) Next() bool {
if i.Released() {
i.err = ErrIterReleased
return false
}
if i.node == 0 {
if !i.forward {
return i.First()
}
return false
}
i.forward = true
i.p.mu.RLock()
defer i.p.mu.RUnlock()
i.node = i.p.nodeData[i.node+nNext]
return i.fill(false, true)
}
func (i *dbIter) Prev() bool {
if i.Released() {
i.err = ErrIterReleased
return false
}
if i.node == 0 {
if i.forward {
return i.Last()
}
return false
}
i.forward = false
i.p.mu.RLock()
defer i.p.mu.RUnlock()
i.node = i.p.findLT(i.key)
return i.fill(true, false)
}
func (i *dbIter) Key() []byte {
return i.key
}
func (i *dbIter) Value() []byte {
return i.value
}
func (i *dbIter) Error() error { return i.err }
func (i *dbIter) Release() {
if !i.Released() {
i.p = nil
i.node = 0
i.key = nil
i.value = nil
i.BasicReleaser.Release()
}
}
const (
nKV = iota
nKey
nVal
nHeight
nNext
)
// DB is an in-memory key/value database.
type DB struct {
cmp comparer.BasicComparer
rnd *rand.Rand
mu sync.RWMutex
kvData []byte
// Node data:
// [0] : KV offset
// [1] : Key length
// [2] : Value length
// [3] : Height
// [3..height] : Next nodes
nodeData []int
prevNode [tMaxHeight]int
maxHeight int
n int
kvSize int
}
func (p *DB) randHeight() (h int) {
const branching = 4
h = 1
for h < tMaxHeight && p.rnd.Int()%branching == 0 {
h++
}
return
}
// Must hold RW-lock if prev == true, as it use shared prevNode slice.
func (p *DB) findGE(key []byte, prev bool) (int, bool) {
node := 0
h := p.maxHeight - 1
for {
next := p.nodeData[node+nNext+h]
cmp := 1
if next != 0 {
o := p.nodeData[next]
cmp = p.cmp.Compare(p.kvData[o:o+p.nodeData[next+nKey]], key)
}
if cmp < 0 {
// Keep searching in this list
node = next
} else {
if prev {
p.prevNode[h] = node
} else if cmp == 0 {
return next, true
}
if h == 0 {
return next, cmp == 0
}
h--
}
}
}
func (p *DB) findLT(key []byte) int {
node := 0
h := p.maxHeight - 1
for {
next := p.nodeData[node+nNext+h]
o := p.nodeData[next]
if next == 0 || p.cmp.Compare(p.kvData[o:o+p.nodeData[next+nKey]], key) >= 0 {
if h == 0 {
break
}
h--
} else {
node = next
}
}
return node
}
func (p *DB) findLast() int {
node := 0
h := p.maxHeight - 1
for {
next := p.nodeData[node+nNext+h]
if next == 0 {
if h == 0 {
break
}
h--
} else {
node = next
}
}
return node
}
// Put sets the value for the given key. It overwrites any previous value
// for that key; a DB is not a multi-map.
//
// It is safe to modify the contents of the arguments after Put returns.
func (p *DB) Put(key []byte, value []byte) error {
p.mu.Lock()
defer p.mu.Unlock()
if node, exact := p.findGE(key, true); exact {
kvOffset := len(p.kvData)
p.kvData = append(p.kvData, key...)
p.kvData = append(p.kvData, value...)
p.nodeData[node] = kvOffset
m := p.nodeData[node+nVal]
p.nodeData[node+nVal] = len(value)
p.kvSize += len(value) - m
return nil
}
h := p.randHeight()
if h > p.maxHeight {
for i := p.maxHeight; i < h; i++ {
p.prevNode[i] = 0
}
p.maxHeight = h
}
kvOffset := len(p.kvData)
p.kvData = append(p.kvData, key...)
p.kvData = append(p.kvData, value...)
// Node
node := len(p.nodeData)
p.nodeData = append(p.nodeData, kvOffset, len(key), len(value), h)
for i, n := range p.prevNode[:h] {
m := n + nNext + i
p.nodeData = append(p.nodeData, p.nodeData[m])
p.nodeData[m] = node
}
p.kvSize += len(key) + len(value)
p.n++
return nil
}
// Delete deletes the value for the given key. It returns ErrNotFound if
// the DB does not contain the key.
//
// It is safe to modify the contents of the arguments after Delete returns.
func (p *DB) Delete(key []byte) error {
p.mu.Lock()
defer p.mu.Unlock()
node, exact := p.findGE(key, true)
if !exact {
return ErrNotFound
}
h := p.nodeData[node+nHeight]
for i, n := range p.prevNode[:h] {
m := n + 4 + i
p.nodeData[m] = p.nodeData[p.nodeData[m]+nNext+i]
}
p.kvSize -= p.nodeData[node+nKey] + p.nodeData[node+nVal]
p.n--
return nil
}
// Contains returns true if the given key are in the DB.
//
// It is safe to modify the contents of the arguments after Contains returns.
func (p *DB) Contains(key []byte) bool {
p.mu.RLock()
_, exact := p.findGE(key, false)
p.mu.RUnlock()
return exact
}
// Get gets the value for the given key. It returns error.ErrNotFound if the
// DB does not contain the key.
//
// The caller should not modify the contents of the returned slice, but
// it is safe to modify the contents of the argument after Get returns.
func (p *DB) Get(key []byte) (value []byte, err error) {
p.mu.RLock()
if node, exact := p.findGE(key, false); exact {
o := p.nodeData[node] + p.nodeData[node+nKey]
value = p.kvData[o : o+p.nodeData[node+nVal]]
} else {
err = ErrNotFound
}
p.mu.RUnlock()
return
}
// Find finds key/value pair whose key is greater than or equal to the
// given key. It returns ErrNotFound if the table doesn't contain
// such pair.
//
// The caller should not modify the contents of the returned slice, but
// it is safe to modify the contents of the argument after Find returns.
func (p *DB) Find(key []byte) (rkey, value []byte, err error) {
p.mu.RLock()
if node, _ := p.findGE(key, false); node != 0 {
n := p.nodeData[node]
m := n + p.nodeData[node+nKey]
rkey = p.kvData[n:m]
value = p.kvData[m : m+p.nodeData[node+nVal]]
} else {
err = ErrNotFound
}
p.mu.RUnlock()
return
}
// NewIterator returns an iterator of the DB.
// The returned iterator is not safe for concurrent use, but it is safe to use
// multiple iterators concurrently, with each in a dedicated goroutine.
// It is also safe to use an iterator concurrently with modifying its
// underlying DB. However, the resultant key/value pairs are not guaranteed
// to be a consistent snapshot of the DB at a particular point in time.
//
// Slice allows slicing the iterator to only contains keys in the given
// range. A nil Range.Start is treated as a key before all keys in the
// DB. And a nil Range.Limit is treated as a key after all keys in
// the DB.
//
// The iterator must be released after use, by calling Release method.
//
// Also read Iterator documentation of the leveldb/iterator package.
func (p *DB) NewIterator(slice *util.Range) iterator.Iterator {
return &dbIter{p: p, slice: slice}
}
// Capacity returns keys/values buffer capacity.
func (p *DB) Capacity() int {
p.mu.RLock()
defer p.mu.RUnlock()
return cap(p.kvData)
}
// Size returns sum of keys and values length. Note that deleted
// key/value will not be accounted for, but it will still consume
// the buffer, since the buffer is append only.
func (p *DB) Size() int {
p.mu.RLock()
defer p.mu.RUnlock()
return p.kvSize
}
// Free returns keys/values free buffer before need to grow.
func (p *DB) Free() int {
p.mu.RLock()
defer p.mu.RUnlock()
return cap(p.kvData) - len(p.kvData)
}
// Len returns the number of entries in the DB.
func (p *DB) Len() int {
p.mu.RLock()
defer p.mu.RUnlock()
return p.n
}
// Reset resets the DB to initial empty state. Allows reuse the buffer.
func (p *DB) Reset() {
p.mu.Lock()
p.rnd = rand.New(rand.NewSource(0xdeadbeef))
p.maxHeight = 1
p.n = 0
p.kvSize = 0
p.kvData = p.kvData[:0]
p.nodeData = p.nodeData[:nNext+tMaxHeight]
p.nodeData[nKV] = 0
p.nodeData[nKey] = 0
p.nodeData[nVal] = 0
p.nodeData[nHeight] = tMaxHeight
for n := 0; n < tMaxHeight; n++ {
p.nodeData[nNext+n] = 0
p.prevNode[n] = 0
}
p.mu.Unlock()
}
// New creates a new initialized in-memory key/value DB. The capacity
// is the initial key/value buffer capacity. The capacity is advisory,
// not enforced.
//
// This DB is append-only, deleting an entry would remove entry node but not
// reclaim KV buffer.
//
// The returned DB instance is safe for concurrent use.
func New(cmp comparer.BasicComparer, capacity int) *DB {
p := &DB{
cmp: cmp,
rnd: rand.New(rand.NewSource(0xdeadbeef)),
maxHeight: 1,
kvData: make([]byte, 0, capacity),
nodeData: make([]int, 4+tMaxHeight),
}
p.nodeData[nHeight] = tMaxHeight
return p
}