bitcask

README

bitcask

This is my toy project to learn golang.

Bitcask is a key-value log database. It produce value in file and store key to value's location to find it. location is consist of

1. fileno
2. offset
3. length

Every time add a key value would append log to a value file and a header file with locations.

And when reading, just find the location and read it from disk. A cache for recent key makes reading faster.

In option.go, there are some options for DB. such as go's cnt for reader, max file size, max key and value length.

I also add location header & checksum to avoid disk fail when loading.

I learn a lot in this project.

1. R/W files and handle errors
2. channel works like a thread safe queue.
3. again importance of tests

There still some works to do. Such as

1. Managing readers to reduce system call of opening same file.
2. A monitor for deleting not outdated logs in files when idle.
3. Appending logs in multiple files, which makes more writers possible.(currently only one)
4. Recover for db's failure. A bug now is that it won't check sucess in creating new value files but not in header files. When this happen, loading return error.

But I want to do some more influential work and have no interest in this toy project anymore.

Documentation

Index

• Variables
• type CacheOption
• type DB
  • func Open(path string, options ...Option) (*DB, error)
  • func (db *DB) Add(key, value string) error
  • func (db *DB) Close()
  • func (db *DB) Get(key string) (string, error)
• type DiskOption
• type Err
  • func (e *Err) Error() string
  • func (e *Err) Unwrap() error
• type FileType
• type LimitOption
• type Option

Variables

var ErrCxtInconsistency = errors.New("cxt: inconsistency")

var ErrCxtInvalid = errors.New("cxt: other files")

var ErrDuplicateOption = errors.New("duplicate option")

var ErrKeyLenTooLong = errors.New("key too long")

var ErrKeyNotFound = errors.New("not found key")

var ErrNotReady = errors.New("not ready")

var ErrRead = errors.New("read")

var ErrValueLenTooLong = errors.New("value too long")

var ErrWrite = errors.New("write")

Types

type CacheOption

type CacheOption struct {
	Capacity int
}

type DB

type DB struct {
	// contains filtered or unexported fields
}

func Open

func Open(path string, options ...Option) (*DB, error)

func (*DB) Add

func (db *DB) Add(key, value string) error

func (*DB) Close

func (db *DB) Close()

func (*DB) Get

func (db *DB) Get(key string) (string, error)

type DiskOption

type DiskOption struct {
	ReaderCnt int
	LoaderCnt int
}

type Err

type Err struct {
	// contains filtered or unexported fields
}

func (*Err) Error

func (e *Err) Error() string

func (*Err) Unwrap

func (e *Err) Unwrap() error

type FileType

type FileType int

const (
	FT_Invalid FileType = iota
	FT_Location
	FT_Data
)

type LimitOption

type LimitOption struct {
	MaxFileSize  int
	MaxKeySize   int
	MaxValueSize int
}

type Option

type Option interface {
	// contains filtered or unexported methods
}