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kv: replace memdb with a more memory efficient version #11807

Merged
merged 12 commits into from
Aug 29, 2019
131 changes: 131 additions & 0 deletions kv/memdb/arena.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,131 @@
// Copyright 2019 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package memdb

import "math"

type arenaAddr struct {
blockIdx uint32
blockOffset uint32
}

func (addr arenaAddr) isNull() bool {
return addr.blockIdx == 0 && addr.blockOffset == 0
}

func newArenaAddr(idx int, offset uint32) arenaAddr {
return arenaAddr{
blockIdx: uint32(idx) + 1,
blockOffset: offset,
}
}

const (
nullBlockOffset = math.MaxUint32
maxBlockSize = 128 << 20
)

type arena struct {
blockSize int
availIdx int
blocks []arenaBlock
}

func newArenaLocator(initBlockSize int) *arena {
return &arena{
blockSize: initBlockSize,
blocks: []arenaBlock{newArenaBlock(initBlockSize)},
}
}

func (a *arena) getFrom(addr arenaAddr) []byte {
return a.blocks[addr.blockIdx-1].getFrom(addr.blockOffset)
}

func (a *arena) alloc(size int) (arenaAddr, []byte) {
if size >= maxBlockSize {
// Use a separate block to store entry which size larger than specified block size.
blk := newArenaBlock(size)
blk.length = size
a.blocks = append(a.blocks, blk)

addr := newArenaAddr(len(a.blocks)-1, 0)
return addr, blk.buf
}

addr, data := a.allocInBlock(a.availIdx, size)
if !addr.isNull() {
return addr, data
}

a.enlarge(size)
return a.allocInBlock(a.availIdx, size)
}

func (a *arena) enlarge(size int) {
a.blockSize <<= 1
for a.blockSize <= size {
a.blockSize <<= 1
}
// Size always less than maxBlockSize.
if a.blockSize > maxBlockSize {
a.blockSize = maxBlockSize
}
a.blocks = append(a.blocks, newArenaBlock(a.blockSize))
a.availIdx = int(uint32(len(a.blocks) - 1))
}

func (a *arena) allocInBlock(idx, size int) (arenaAddr, []byte) {
offset, data := a.blocks[idx].alloc(size)
if offset == nullBlockOffset {
return arenaAddr{}, nil
}
return newArenaAddr(idx, offset), data
}

func (a *arena) reset() {
a.availIdx = 0
a.blockSize = len(a.blocks[0].buf)
a.blocks = []arenaBlock{a.blocks[0]}
a.blocks[0].reset()
}

type arenaBlock struct {
buf []byte
length int
}

func newArenaBlock(blockSize int) arenaBlock {
return arenaBlock{
buf: make([]byte, blockSize),
}
}

func (a *arenaBlock) getFrom(offset uint32) []byte {
return a.buf[offset:]
}

func (a *arenaBlock) alloc(size int) (uint32, []byte) {
offset := a.length
newLen := offset + size
if newLen > len(a.buf) {
return nullBlockOffset, nil
}
a.length = newLen
return uint32(offset), a.buf[offset : offset+size]
}

func (a *arenaBlock) reset() {
a.length = 0
}
102 changes: 102 additions & 0 deletions kv/memdb/iterator.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,102 @@
// Copyright 2019 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package memdb

import "unsafe"

// Iterator iterates the entries in the DB.
type Iterator struct {
db *DB
curr *node
key []byte
val []byte
}

// NewIterator returns a new Iterator for the lock store.
func (db *DB) NewIterator() Iterator {
return Iterator{
db: db,
}
}

// Valid returns true if the iterator is positioned at a valid node.
func (it *Iterator) Valid() bool { return it.curr != nil }

// Key returns the key at the current position.
func (it *Iterator) Key() []byte {
return it.key
}

// Value returns value.
func (it *Iterator) Value() []byte {
return it.val
}

// Next moves the iterator to the next entry.
func (it *Iterator) Next() {
it.changeToAddr(it.curr.nexts[0])
}

// Prev moves the iterator to the previous entry.
func (it *Iterator) Prev() {
it.changeToAddr(it.curr.prev)
}

// Seek locates the iterator to the first entry with a key >= seekKey.
func (it *Iterator) Seek(seekKey []byte) {
node, nodeData, _ := it.db.findGreaterEqual(seekKey) // find >=.
it.updateState(node, nodeData)
}

// SeekForPrev locates the iterator to the last entry with key <= target.
func (it *Iterator) SeekForPrev(target []byte) {
node, nodeData, _ := it.db.findLess(target, true) // find <=.
it.updateState(node, nodeData)
}

// SeekForExclusivePrev locates the iterator to the last entry with key < target.
func (it *Iterator) SeekForExclusivePrev(target []byte) {
node, nodeData, _ := it.db.findLess(target, false)
it.updateState(node, nodeData)
}

// SeekToFirst locates the iterator to the first entry.
func (it *Iterator) SeekToFirst() {
node, nodeData := it.db.getNext(it.db.head.node, 0)
it.updateState(node, nodeData)
}

// SeekToLast locates the iterator to the last entry.
func (it *Iterator) SeekToLast() {
node, nodeData := it.db.findLast()
it.updateState(node, nodeData)
}

func (it *Iterator) updateState(node *node, nodeData []byte) {
it.curr = node
if node != nil {
it.key = node.getKey(nodeData)
it.val = node.getValue(nodeData)
}
}

func (it *Iterator) changeToAddr(addr arenaAddr) {
var data []byte
var n *node
if !addr.isNull() {
data = it.db.arena.getFrom(addr)
n = (*node)(unsafe.Pointer(&data[0]))
}
it.updateState(n, data)
}
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