// 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 + nNext + 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. // // WARNING: Any slice returned by interator (e.g. slice returned by calling // Iterator.Key() or Iterator.Key() methods), its content should not be modified // unless noted otherwise. // // 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 }