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kv: replace memdb with a more memory efficient version (#11807)
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// 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. | ||
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package memdb | ||
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import "math" | ||
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type arenaAddr struct { | ||
blockIdx uint32 | ||
blockOffset uint32 | ||
} | ||
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func (addr arenaAddr) isNull() bool { | ||
return addr.blockIdx == 0 && addr.blockOffset == 0 | ||
} | ||
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func newArenaAddr(idx int, offset uint32) arenaAddr { | ||
return arenaAddr{ | ||
blockIdx: uint32(idx) + 1, | ||
blockOffset: offset, | ||
} | ||
} | ||
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const ( | ||
nullBlockOffset = math.MaxUint32 | ||
maxBlockSize = 128 << 20 | ||
) | ||
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type arena struct { | ||
blockSize int | ||
availIdx int | ||
blocks []arenaBlock | ||
} | ||
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func newArenaLocator(initBlockSize int) *arena { | ||
return &arena{ | ||
blockSize: initBlockSize, | ||
blocks: []arenaBlock{newArenaBlock(initBlockSize)}, | ||
} | ||
} | ||
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func (a *arena) getFrom(addr arenaAddr) []byte { | ||
return a.blocks[addr.blockIdx-1].getFrom(addr.blockOffset) | ||
} | ||
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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) | ||
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addr := newArenaAddr(len(a.blocks)-1, 0) | ||
return addr, blk.buf | ||
} | ||
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addr, data := a.allocInBlock(a.availIdx, size) | ||
if !addr.isNull() { | ||
return addr, data | ||
} | ||
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a.enlarge(size) | ||
return a.allocInBlock(a.availIdx, size) | ||
} | ||
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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)) | ||
} | ||
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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 | ||
} | ||
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func (a *arena) reset() { | ||
a.availIdx = 0 | ||
a.blockSize = len(a.blocks[0].buf) | ||
a.blocks = []arenaBlock{a.blocks[0]} | ||
a.blocks[0].reset() | ||
} | ||
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type arenaBlock struct { | ||
buf []byte | ||
length int | ||
} | ||
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func newArenaBlock(blockSize int) arenaBlock { | ||
return arenaBlock{ | ||
buf: make([]byte, blockSize), | ||
} | ||
} | ||
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func (a *arenaBlock) getFrom(offset uint32) []byte { | ||
return a.buf[offset:] | ||
} | ||
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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] | ||
} | ||
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func (a *arenaBlock) reset() { | ||
a.length = 0 | ||
} |
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// 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. | ||
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package memdb | ||
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import "unsafe" | ||
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// Iterator iterates the entries in the DB. | ||
type Iterator struct { | ||
db *DB | ||
curr *node | ||
key []byte | ||
val []byte | ||
} | ||
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// NewIterator returns a new Iterator for the lock store. | ||
func (db *DB) NewIterator() Iterator { | ||
return Iterator{ | ||
db: db, | ||
} | ||
} | ||
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// Valid returns true if the iterator is positioned at a valid node. | ||
func (it *Iterator) Valid() bool { return it.curr != nil } | ||
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// Key returns the key at the current position. | ||
func (it *Iterator) Key() []byte { | ||
return it.key | ||
} | ||
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// Value returns value. | ||
func (it *Iterator) Value() []byte { | ||
return it.val | ||
} | ||
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// Next moves the iterator to the next entry. | ||
func (it *Iterator) Next() { | ||
it.changeToAddr(it.curr.nexts[0]) | ||
} | ||
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// Prev moves the iterator to the previous entry. | ||
func (it *Iterator) Prev() { | ||
it.changeToAddr(it.curr.prev) | ||
} | ||
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// 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) | ||
} | ||
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// 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) | ||
} | ||
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// 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) | ||
} | ||
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// 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) | ||
} | ||
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// SeekToLast locates the iterator to the last entry. | ||
func (it *Iterator) SeekToLast() { | ||
node, nodeData := it.db.findLast() | ||
it.updateState(node, nodeData) | ||
} | ||
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func (it *Iterator) updateState(node *node, nodeData []byte) { | ||
it.curr = node | ||
if node != nil { | ||
it.key = node.getKey(nodeData) | ||
it.val = node.getValue(nodeData) | ||
} | ||
} | ||
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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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