Compact Base64-first Database-friendly UIDs

• Compact
  20 characters encode 120 bits of payload.
• Efficient
  Speedy encoding and decoding.
• Compatible
  Can be used in URLs, form-fields and as HTML attributes.
• Lexicographically ordered
  The bitstring and the encoded string sort the same.
• Database-friendly
  Time-prefix improves database locality and performance.

Structure of a BaseUid

A BaseUid consist of two parts:

1. 48bits of POSIX time in nanoseconds, left-shifted by 2 bits
2. 72bits of randomness

This selection ensures that the resulting Base64-encoded string starts with a letter for timestamps between the years 2021 and 2260. This allows the use of BaseUids in places that do not allow values starting with a digit.¹

These two parts are concatenated into a 120bit long bitstring ...

         8      16      24      32      40      48      56      64      72      80      88      96      104     112     120
┏━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┓
┃               time (00-47)                    ┆                               rnd (48-119)                            ┃
┗━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┛

... which is then converted to an ASCII string using the lexicographically-ordered Base64 alphabet ...
-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz
... resulting in 20 characters, of which 8 characters represent the time-component and 12 characters represent the randomness-component.

For example, a BaseUid from the start of 2022 could be ANjssJkyfa3H00J9ZPJG.
ANjssJky is the timestamp-component for 2022-01-01T00:00:00Z and fa3H00J9ZPJG is the randomness-component that differs with each generated value, even if the point in time stays the same.

Conversion to UUIDv8 Format

BaseUids can easily be converted into UUIDv8 format if required:

         8      16      24      32      40      48      56      64      72      80      88      96      104     112     120     128
┏━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┓
┃               time (00-47)                    ┆VER┆rnd (52-63)┆V┆             rnd (66-125)                                  ┆Z┃
┗━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┛
                                                 ^               ^                                                             ^
                                                 |               |                                                             |
                                              ┌VER (constant)┐  ┌VAR (constant)┐                                   ┌Z (constant)┐
                                              │ 1 0 0 0      │  │ 1 0          │                                   │ 0 0        │
                                              └──────────────┘  └──────────────┘                                   └────────────┘

Comparison with other UID formats

	Payload	Compact	Efficient	Compatible	Ordered	Database-friendly
BaseUID	120bits	✔ Base64	✔	✔	✔	✔
UUID text repr.	128bits	✖ Base16	✔	✖	✔	✖
ULID	128bits	🞈 Base32	🞈	✖	✔	✔
LexicalUUID	128bits	✖ Base16	✖	✖	✔	✔
Flake	128bits	✔ Base62	✖	✖	❔	✔
ShardingID	64bits	✖ Base10	🞈	✖	✔	✔
KSUID	160bits	✔ Base62	✖	✖	✔	✔
Elasticflake	120bits	✔ Base64	✔	✖	✖	✔
FlakeID	64bits	✖ Base10/16	✔	✖	✔	✔
Sonyflake	64bits	✖	✔	✖	✔	✔
orderedUuid	120bits	✖ Base10	✔	✖	✖	✔
COMBGUID	120bits	✖ Base10	✔	✖	✖	✔
SID	128bits	✔ Base10/16/32/64	✔	✖	✔	✔
pushID	120bits	✔ Base64	✔	✖	✔	✔
XID	96bits	🞈 Base32	✔	✖	✔	✔
ObjectID	96bits	✖ Base16	✔	✖	✔	✔
CUID	❔	✖ Base36	✖	✔	✖	✔

Footnotes

1. Such as HTML attributes values, which are required to be valid CSS identifiers. ↩