# Small UID
⚠️ _This project is in experimental phase, the API may may be subject to change._
This is a rust implementation of [Small UID](https://github.com/Mediagone/small-uid) by [Mediagone](https://github.com/Mediagone).
UUIDs are frequently used as database _Primary Key_ in software development. However, they aren't the best choice mainly due to their random sorting and the resulting fragmentation in databases indexes.
Using [ULIDs](https://github.com/ulid/spec) is generally a very good alternative, solving most of UUID flaws.
**Small UIDs** are also an ideal alternative **when you do not need as much uniqueness** and want **shorter "user-friendly" encoded strings**.
## Introduction
Small UIDs are short unique identifiers especially designed to be used as efficient database _Primary Key_:
- Half smaller than UUID / ULID (64-bit)
- Lexicographically sortable
- Encodable as a short user-friendly and URL-safe base-64 string (`a-zA-Z0-9_-`)
- User-friendly strings are generated in a way to be always very different (no shared prefix due to similar timestamps)
|Size|64 bits|128 bits|128 bits|
|Monotonic sort order|Yes ***|Yes|No|
|Random bits| 20 | 80 |122|
|Collision odds **| 1,024 _/ ms*_ | 1.099e+12 _/ ms*_| 2.305e+18 |
* _theorical number of generated uids before the first expected collision._\
** _the uid includes a timestamp, so collisions may occur only during the same millisecond._\
*** _monotonic sort order, but random order when generated at the same millisecond._
They are internally stored as _64-bit_ integers (_44-bit_ timestamp followed by _20 random bits_):
|-----------------------| |------------|
Timestamp Randomness
44 bits 20 bits
The random number suffix still guarantees a decent amount of uniqueness when many ids are created in the same millisecond (up to 1,048,576 different values) and you may only expect collision if you're generating more than 1024 random ids during the same millisecond.
### Sorting
Because of the sequential timestamp, _Small UIDs_ are naturally sorted chronologically. It **improves indexing** when inserting values in databases, new ids being appended to the end of the table without reshuffling existing data (read more [in this article](https://www.codeproject.com/Articles/388157/GUIDs-as-fast-primary-keys-under-multiple-database)).
However, **sort order within the same millisecond is not guaranteed** because of the random bits suffix.
## Examples of usage
### Generating Small UIDs
```rust
let smalluid1 = SmallUid::new().unwrap();
let smalluid2 = SmallUid::try_from("GSntNvOw6n8".to_string()).unwrap();
```
### Converting Small UIDs
```rust
let smalluid = SmallUid::new().unwrap();
let uid_string = smalluid.to_string();
```