simpledb

Documentation

Overview

Package simpledb implements a one-table version of LevelDB

It buffers all writes in memory; to make data durable, call Compact(). This operation re-writes all of the data in the database (including in-memory writes) in a crash-safe manner. Keys in the table are cached for efficient reads.

Index

• func Close(db Database)
• func CloseTable(t Table)
• func Compact(db Database)
• func DecodeUInt64(p []byte) (uint64, uint64)
• func EncodeSlice(data []byte, p []byte) []byte
• func EncodeUInt64(x uint64, p []byte) []byte
• func Read(db Database, k uint64) ([]byte, bool)
• func Shutdown(db Database)
• func Write(db Database, k uint64, v []byte)
• type Database
  • func NewDb() Database
  • func Recover() Database
• type Entry
  • func DecodeEntry(data []byte) (Entry, uint64)
• type Table
  • func CreateTable(p string) Table
  • func RecoverTable(p string) Table

Functions

func Close

func Close(db Database)

Close closes an open database cleanly, flushing any in-memory writes.

db should not be used afterward

func CloseTable

func CloseTable(t Table)

CloseTable frees up the fd held by a table.

func Compact

func Compact(db Database)

Compact persists in-memory writes to a new table.

This simple database design must re-write all data to combine in-memory writes with existing writes.

func DecodeUInt64

func DecodeUInt64(p []byte) (uint64, uint64)

DecodeUInt64 is a Decoder(uint64)

All decoders have the shape func(p []byte) (T, uint64)

The uint64 represents the number of bytes consumed; if 0, then decoding failed, and the value of type T should be ignored.

func EncodeSlice

func EncodeSlice(data []byte, p []byte) []byte

EncodeSlice is an Encoder([]byte)

func EncodeUInt64

func EncodeUInt64(x uint64, p []byte) []byte

EncodeUInt64 is an Encoder(uint64)

func Read

func Read(db Database, k uint64) ([]byte, bool)

Read gets a key from the database.

Returns a boolean indicating if the k was found and a non-nil slice with the value if k was in the database.

Reflects any completed in-memory writes.

func Shutdown

func Shutdown(db Database)

Shutdown immediately closes the database.

Discards any uncommitted in-memory writes; similar to a crash except for cleanly closing any open files.

func Write

func Write(db Database, k uint64, v []byte)

Write sets a key to a new value.

Creates a new key-value mapping if k is not in the database and overwrites the previous value if k is present.

The new value is buffered in memory. To persist it, call db.Compact().

Types

type Database

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

Database is a handle to an open database.

func NewDb

func NewDb() Database

NewDb initializes a new database on top of an empty filesys.

func Recover

func Recover() Database

Recover restores a previously created database after a crash or shutdown.

type Entry

type Entry struct {
	Key   uint64
	Value []byte
}

Entry represents a (key, value) pair.

func DecodeEntry

func DecodeEntry(data []byte) (Entry, uint64)

DecodeEntry is a Decoder(Entry)

type Table

type Table struct {
	Index map[uint64]uint64
	File  filesys.File
}

A Table provides access to an immutable copy of data on the filesystem, along with an index for fast random access.

func CreateTable

func CreateTable(p string) Table

CreateTable creates a new, empty table.

func RecoverTable

func RecoverTable(p string) Table

RecoverTable restores a table from disk on startup.