xid

README

Globally Unique ID Generator

REPO: https://github.com/rs/xid

Package xid is a globally unique id generator library, ready to be used safely directly in your server code.

Xid is using Mongo Object ID algorithm to generate globally unique ids with a different serialization (base64) to make it shorter when transported as a string: https://docs.mongodb.org/manual/reference/object-id/

• 4-byte value representing the seconds since the Unix epoch,
• 3-byte machine identifier,
• 2-byte process id, and
• 3-byte counter, starting with a random value.

The binary representation of the id is compatible with Mongo 12 bytes Object IDs. The string representation is using base32 hex (w/o padding) for better space efficiency when stored in that form (20 bytes). The hex variant of base32 is used to retain the sortable property of the id.

Xid doesn't use base64 because case sensitivity and the 2 non alphanum chars may be an issue when transported as a string between various systems. Base36 wasn't retained either because 1/ it's not standard 2/ the resulting size is not predictable (not bit aligned) and 3/ it would not remain sortable. To validate a base32 xid, expect a 20 chars long, all lowercase sequence of a to v letters and 0 to 9 numbers ([0-9a-v]{20}).

UUIDs are 16 bytes (128 bits) and 36 chars as string representation. Twitter Snowflake ids are 8 bytes (64 bits) but require machine/data-center configuration and/or central generator servers. xid stands in between with 12 bytes (96 bits) and a more compact URL-safe string representation (20 chars). No configuration or central generator server is required so it can be used directly in server's code.

Name	Binary Size	String Size	Features
UUID	16 bytes	36 chars	configuration free, not sortable
shortuuid	16 bytes	22 chars	configuration free, not sortable
Snowflake	8 bytes	up to 20 chars	needs machin/DC configuration, needs central server, sortable
MongoID	12 bytes	24 chars	configuration free, sortable
xid	12 bytes	20 chars	configuration free, sortable

Features:

• Size: 12 bytes (96 bits), smaller than UUID, larger than snowflake
• Base32 hex encoded by default (20 chars when transported as printable string, still sortable)
• Non configured, you don't need set a unique machine and/or data center id
• K-ordered
• Embedded time with 1 second precision
• Unicity guaranteed for 16,777,216 (24 bits) unique ids per second and per host/process
• Lock-free (i.e.: unlike UUIDv1 and v2)

Best used with zerolog's RequestIDHandler.

Notes:

• Xid is dependent on the system time, a monotonic counter and so is not cryptographically secure. If unpredictability of IDs is important, you should not use Xids. It is worth noting that most of the other UUID like implementations are also not cryptographically secure. You shoud use libraries that rely on cryptographically secure sources (like /dev/urandom on unix, crypto/rand in golang), if you want a truly random ID generator.

References:

• http://www.slideshare.net/davegardnerisme/unique-id-generation-in-distributed-systems
• https://en.wikipedia.org/wiki/Universally_unique_identifier
• https://blog.twitter.com/2010/announcing-snowflake
• Python port by Graham Abbott: https://github.com/graham/python_xid
• Scala port by Egor Kolotaev: https://github.com/kolotaev/ride

Install

go get github.com/rs/xid

Usage

guid := xid.New()

println(guid.String())
// Output: 9m4e2mr0ui3e8a215n4g

Get xid embedded info:

guid.Machine()
guid.Pid()
guid.Time()
guid.Counter()

Benchmark

Benchmark against Go Maxim Bublis's UUID.

BenchmarkXID        	20000000	        91.1 ns/op	      32 B/op	       1 allocs/op
BenchmarkXID-2      	20000000	        55.9 ns/op	      32 B/op	       1 allocs/op
BenchmarkXID-4      	50000000	        32.3 ns/op	      32 B/op	       1 allocs/op
BenchmarkUUIDv1     	10000000	       204 ns/op	      48 B/op	       1 allocs/op
BenchmarkUUIDv1-2   	10000000	       160 ns/op	      48 B/op	       1 allocs/op
BenchmarkUUIDv1-4   	10000000	       195 ns/op	      48 B/op	       1 allocs/op
BenchmarkUUIDv4     	 1000000	      1503 ns/op	      64 B/op	       2 allocs/op
BenchmarkUUIDv4-2   	 1000000	      1427 ns/op	      64 B/op	       2 allocs/op
BenchmarkUUIDv4-4   	 1000000	      1452 ns/op	      64 B/op	       2 allocs/op

Note: UUIDv1 requires a global lock, hence the performence degrading as we add more CPUs.

Licenses

All source code is licensed under the MIT License.

Documentation

Overview

Package xid is a globally unique id generator suited for web scale

Xid is using Mongo Object ID algorithm to generate globally unique ids: https://docs.mongodb.org/manual/reference/object-id/

• 4-byte value representing the seconds since the Unix epoch,
• 3-byte machine identifier,
• 2-byte process id, and
• 3-byte counter, starting with a random value.

The binary representation of the id is compatible with Mongo 12 bytes Object IDs. The string representation is using base32 hex (w/o padding) for better space efficiency when stored in that form (20 bytes). The hex variant of base32 is used to retain the sortable property of the id.

Xid doesn't use base64 because case sensitivity and the 2 non alphanum chars may be an issue when transported as a string between various systems. Base36 wasn't retained either because 1/ it's not standard 2/ the resulting size is not predictable (not bit aligned) and 3/ it would not remain sortable. To validate a base32 `xid`, expect a 20 chars long, all lowercase sequence of `a` to `v` letters and `0` to `9` numbers (`[0-9a-v]{20}`).

UUID is 16 bytes (128 bits), snowflake is 8 bytes (64 bits), xid stands in between with 12 bytes with a more compact string representation ready for the web and no required configuration or central generation server.

Features:

• Size: 12 bytes (96 bits), smaller than UUID, larger than snowflake
• Base32 hex encoded by default (16 bytes storage when transported as printable string)
• Non configured, you don't need set a unique machine and/or data center id
• K-ordered
• Embedded time with 1 second precision
• Unicity guaranteed for 16,777,216 (24 bits) unique ids per second and per host/process

Best used with xlog's RequestIDHandler (https://godoc.org/github.com/rs/xlog#RequestIDHandler).

References:

• http://www.slideshare.net/davegardnerisme/unique-id-generation-in-distributed-systems
• https://en.wikipedia.org/wiki/Universally_unique_identifier
• https://blog.twitter.com/2010/announcing-snowflake

Index

• Variables
• func Sort(ids []ID)
• type ID
  • func FromBytes(b []byte) (ID, error)
  • func FromString(id string) (ID, error)
  • func New() ID
  • func NewWithTime(t time.Time) ID
  • func NilID() ID
  • func (id ID) Bytes() []byte
  • func (id ID) Compare(other ID) int
  • func (id ID) Counter() int32
  • func (id ID) IsNil() bool
  • func (id ID) Machine() []byte
  • func (id ID) MarshalJSON() ([]byte, error)
  • func (id ID) MarshalText() ([]byte, error)
  • func (id ID) Pid() uint16
  • func (id *ID) Scan(value interface{}) (err error)
  • func (id ID) String() string
  • func (id ID) Time() time.Time
  • func (id *ID) UnmarshalJSON(b []byte) error
  • func (id *ID) UnmarshalText(text []byte) error
  • func (id ID) Value() (driver.Value, error)

Variables

var (
	// ErrInvalidID is returned when trying to unmarshal an invalid ID
	ErrInvalidID = errors.New("xid: invalid ID")
)

Functions

func Sort

func Sort(ids []ID)

Sort sorts an array of IDs inplace. It works by wrapping `[]ID` and use `sort.Sort`.

Types

type ID

type ID [rawLen]byte

ID represents a unique request id

func FromBytes

func FromBytes(b []byte) (ID, error)

FromBytes convert the byte array representation of `ID` back to `ID`

func FromString

func FromString(id string) (ID, error)

FromString reads an ID from its string representation

func New

func New() ID

New generates a globally unique ID

func NewWithTime

func NewWithTime(t time.Time) ID

NewWithTime generates a globally unique ID with the passed in time

func NilID

func NilID() ID

NilID returns a zero value for `xid.ID`.

func (ID) Bytes

func (id ID) Bytes() []byte

Bytes returns the byte array representation of `ID`

func (ID) Compare

func (id ID) Compare(other ID) int

Compare returns an integer comparing two IDs. It behaves just like `bytes.Compare`. The result will be 0 if two IDs are identical, -1 if current id is less than the other one, and 1 if current id is greater than the other.

func (ID) Counter

func (id ID) Counter() int32

Counter returns the incrementing value part of the id. It's a runtime error to call this method with an invalid id.

func (ID) IsNil

func (id ID) IsNil() bool

IsNil Returns true if this is a "nil" ID

func (ID) Machine

func (id ID) Machine() []byte

Machine returns the 3-byte machine id part of the id. It's a runtime error to call this method with an invalid id.

func (ID) MarshalJSON

func (id ID) MarshalJSON() ([]byte, error)

MarshalJSON implements encoding/json Marshaler interface

func (ID) MarshalText

func (id ID) MarshalText() ([]byte, error)

MarshalText implements encoding/text TextMarshaler interface

func (ID) Pid

func (id ID) Pid() uint16

Pid returns the process id part of the id. It's a runtime error to call this method with an invalid id.

func (*ID) Scan

func (id *ID) Scan(value interface{}) (err error)

Scan implements the sql.Scanner interface.

func (ID) String

func (id ID) String() string

String returns a base32 hex lowercased with no padding representation of the id (char set is 0-9, a-v).

func (ID) Time

func (id ID) Time() time.Time

Time returns the timestamp part of the id. It's a runtime error to call this method with an invalid id.

func (*ID) UnmarshalJSON

func (id *ID) UnmarshalJSON(b []byte) error

UnmarshalJSON implements encoding/json Unmarshaler interface

func (*ID) UnmarshalText

func (id *ID) UnmarshalText(text []byte) error

UnmarshalText implements encoding/text TextUnmarshaler interface

func (ID) Value

func (id ID) Value() (driver.Value, error)

Value implements the driver.Valuer interface.