README
¶
Globally Unique ID Generator
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 (bast64) 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
Best used with xlog's 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
Install
go get github.com/cool-rest/xid
Usage
guid := xid.New()
println(guid.String())
// Output: 9m4e2mr0ui3e8a215n4g
Get xid embedded info:
guid.Machine()
guid.Pid()
guid.Time()
guid.Counter()
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 guaranted for 16,777,216 (20 bits) unique ids per second and per host/process
Best used with xlog's RequestIDHandler (https://godoc.org/github.com/cool-rest/xlog#RequestIDHandler).
References:
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrInvalidID = errors.New("invalid ID")
ErrInvalidID is returned when trying to unmarshal an invalid ID
Functions ¶
This section is empty.
Types ¶
type ID ¶
type ID [rawLen]byte
ID represents a unique request id
func FromString ¶
FromString reads an ID from its string representation
func (ID) Counter ¶
Counter returns the incrementing value part of the id. It's a runtime error to call this method with an invalid id.
func (ID) Machine ¶
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) MarshalText ¶
MarshalText implements encoding/text TextMarshaler interface
func (ID) Pid ¶
Pid returns the process id part of the id. It's a runtime error to call this method with an invalid id.
func (ID) String ¶
String returns a base32 hex lowercased with no padding representation of the id (char set is 0-9, a-v).
func (ID) Time ¶
Time returns the timestamp part of the id. It's a runtime error to call this method with an invalid id.
func (*ID) UnmarshalText ¶
UnmarshalText implements encoding/text TextUnmarshaler interface
Source Files