tiny-bitcask
simple kv store engine inspired by bitcask
Inspired By BitCask
System Design
-
DB启动时，系统内存储着
merged-data-file与hint-file -
系统通过读取
hint-file一次性拉取索引文件到内存中
hint-file结构：timestamp | key-size | value-size | value-pos | key
- 再创建一个新的文件用于存放新写入的entry
- 写入entry时，先写磁盘再写内存哈希索引
- 当一个文件写满时，关闭此文件，创建新文件
- 后台线程将
old-file合并到merged-data-file，重写hint-file - 当数据库关闭时，强制merge，保证系统中存放着两份文件
DataBase API Design
// Open database instance
func Open(dir string, cfg *Config)*DB
// Get Retrieve a value by key from a Bitcask datastore.
func (d *DB) Get(key []byte) ([]byte, error)
// Put Store a key and value in a Bitcask datastore.
func (d *DB) Put(key, value []byte)error
// Delete a key from a Bitcask datastore.
func (d *DB) Delete(key []byte)error
// ListKeys List all keys in a Bitcask datastore.
func (d *DB) ListKeys()[][]byte
// Fold over all K/V pairs in a Bitcask datastore.
// Fun is expected to be of the form: F(K,V,Acc0) → Acc.
func (d *DB) fold()
// merge Merge several data files within a Bitcask datastore into a more compact form.
// Also, produce hintfiles for faster startup.
func (d *DB) merge(dir string) bool
// sync Force any writes to sync to disk.
func (d *DB) sync() bool
// Close a Bitcask data store and flush all pending writes (if any) to disk.
func (d *DB) Close() bool
TODO-LIST
- 完善内存哈希索引模块，在单个文件条件下测试
GET/PUT接口 - 增加
mode字段 用来区分entry的操作类型 - 拓展多文件，实现
older、active file的区别 - 实现后台
merge功能，生成merged-data-file与hint-file
