blog/content/sundries/presenting-julids/index.md

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2023-07-29 23:46:18 +00:00
+++
title = "Presenting Julids: another fine sundry, by Nebcorp Heavy Industries and Sundries"
slug = "presenting-julids"
date = "2023-07-29"
[taxonomies]
tags = ["software", "sundry", "proclamation", "sqlite", "rust", "ulid", "julid"]
+++
# Presenting Julids
Nebcorp Heavy Industries and Sundries, long a world leader in sundries, is proud to present the
official globally unique sortable identifier type for all Nebcorp HIAS', and all Nebcorp companies'
database entities, [Julids](https://gitlab.com/nebkor/julid). Julids are globally unique sortable
identifiers, backwards-compatible with [ULIDs](https://github.com/ulid/spec).
Inside your Rust program, simply add `julid-rs` to your project's `Cargo.toml` file, and use it
like:
``` rust
use julid::Julid;
fn main() {
let id = Julid::new();
dbg!(id.created_at(), id.as_string());
}
```
Such a program would output something like:
``` text
[main.rs:2] id.created_at() = 2023-07-29T20:21:50.009Z
[main.rs:2] id.as_string() = "01H6HN10SS00020YT344XMGA3C"
```
However, it can also be built as a [loadable extension](https://www.sqlite.org/loadext.html) for
SQLite, adding database functions for creating and querying Julids:
``` text
$ sqlite3
SQLite version 3.40.1 2022-12-28 14:03:47
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> .load ./libjulid
sqlite> select hex(julid_new());
018998768ACF000060B31DB175E0C5F9
sqlite> select julid_string(julid_new());
01H6C7D9CT00009TF3EXXJHX4Y
sqlite> select julid_seconds(julid_new());
1690480066.208
sqlite> select datetime(julid_timestamp(julid_new()), 'auto');
2023-07-27 17:47:50
sqlite> select julid_counter(julid_new());
0
```
## Julids vs ULIDs
Julids are a drop-in replacement for ULIDs; all Julids are valid ULIDs, but not all ULIDs are valid Julids.
Given their compatibility relationship, Julids and ULIDs must have quite a bit in common, and indeed
they do:
* they are 128-bits long
* they are lexicographically sortable
* they encode their creation time as the number of milliseconds since the [UNIX
epoch](https://en.wikipedia.org/wiki/Unix_time)
* their string representation is a 26-character [base-32
Crockford](https://en.wikipedia.org/wiki/Base32) encoding of their big-endian bytes
* IDs created within the same millisecond are still meant to sort in their order of creation
Julids and ULIDs have different ways to implement that last piece. If you look at the layout of bits
in a ULID, they look like this:
![ULID bit structure](./ulid.svg)
According to the ULID spec, for ULIDs created in the same millisecond, the least-significant bit
should be incremented for each new ID. Since that portion of the ULID is random, that means you may
not be able to increment it without spilling into the timestamp portion. Likewise, it's easy to
guess a new possibly-valid ULID simply by incrementing an already-known one. And finally, this means
that sorting will need to read all the way to the end of the ULID for IDs created in the same
millisecond.
To address these shortcomings, Julids (Joe's ULIDs) have the following structure:
![Julid bit structure](./julid.svg)
As with ULIDs, the 48 most-significant bits encode the time of creation. Unlike ULIDs, the next 16
most-significant bits are not random: they're a monotonic counter for IDs created within the same
millisecond[^monotonic]. Since it's only 16 bits, it will saturate after 65,536 IDs intra-millisecond creations,
after which, IDs in that same millisecond will not have an intrinsic total order (the random bits
will still be different, so you shouldn't have collisions). My PC, which is no slouch, can only
generate about 20,000 per millisecond, so hopefully this is not an issue! Because the random bits
are always fresh, it's not possible to easily guess a valid Julid if you already have a different
valid one.
# How to use
As mentioned, the Julid crate can be used in two different ways: as a regular Rust library, declared
in your Rust project's `Cargo.toml` file (say, by running `cargo add julid-rs`), and used as also
shown above. There's a rudimentary
[benchmark](https://gitlab.com/nebkor/julid/-/blob/main/examples/benchmark.rs) example in the repo,
which I'll talk more about below. But the primary use case for me was as a loadable SQLite
extension, as I [previously
wrote](/rnd/one-part-serialized-mystery-part-2/#next-steps-with-ids). Both are covered in the
[documentation](https://docs.rs/julid-rs/latest/julid/), but let's go over them here, starting with
the extension.
## Inside SQLite as a loadable extension
The extension, when loaded into SQLite, provides the following functions:
* `julid_new()`: create a new Julid and return it as a 16-byte
[blob](https://www.sqlite.org/datatype3.html#storage_classes_and_datatypes)
* `julid_seconds(julid)`: get the number seconds (as a 64-bit float) since the UNIX epoch that this
julid was created
* `julid_counter(julid)`: show the value of this julid's monotonic counter
* `julid_sortable(julid)`: return the 64-bit concatenation of the timestamp and counter
* `julid_string(julid)`: show the [base-32 Crockford](https://en.wikipedia.org/wiki/Base32)
encoding of this julid; the raw bytes won't be valid UTF-8, so use this or the built-in `hex()`
function to `select` a human-readable representation
### Building and loading
If you want to use it as a SQLite extension:
* clone the [repo](https://gitlab.com/nebkor/julid)
* build it with `cargo build --features plugin` (this builds the SQLite extension)
* copy the resulting `libjulid.[so|dylib|whatevs]` to some place where you can...
* load it into SQLite with `.load /path/to/libjulid` as shown at the top
* party
If you, like me, wish to use Julids as primary keys, just create your table like:
``` sql
create table users (
id blob not null primary key default (julid_new()),
...
);
```
and you've got a first-class ticket straight to Julid City, baby!
For a table created like:
``` sql
-- table of things to watch
create table if not exists watches (
id blob not null primary key default (julid_new()),
kind int not null, -- enum for movie or tv show or whatev
title text not null,
metadata_url text, -- possible url for imdb or other metadata-esque site to show the user
length int,
release_date int,
added_by blob not null, -- ID of the user that added it
last_updated int not null default (unixepoch()),
foreign key (added_by) references users (id)
);
```
and then [some
code](https://gitlab.com/nebkor/ww/-/blob/main/src/import_utils.rs?ref_type=heads#L92-126) that
inserted rows into that table like
``` sql
insert into watches (kind, title, length, release_date, added_by) values (?,?,?,?,?)
```
where the wildcards get bound in a loop with unique values and the Julid `id` field is
generated by the extension for each row, I get over 100,000 insertions/second.
## Inside a Rust program
Of course, you can also use it outside of a database; the `Julid` type is publicly exported. There's
a simple benchmark in the examples folder of the repo, the important parts of which look like:
``` rust
use julid::Julid;
fn main() {
[....]
let start = Instant::now();
for _ in 0..num {
v.push(Julid::new());
}
let end = Instant::now();
let dur = (end - start).as_micros();
for id in v.iter() {
eprintln!(
"{id}: created_at {}; counter: {}; sortable: {}",
id.created_at(),
id.counter(),
id.sortable()
);
}
println!("{num} Julids generated in {dur}us");
```
If you were to run it on a computer like mine[^my computer], you might see something like this:
``` text
$ cargo run --example=benchmark --release -- -n 30000 2> /dev/null
30000 Julids generated in 1240us
```
That's about 24,000 IDs/millisecond; 24 *MILLION* per second!
The default optional Cargo features include implementations of traits for getting Julids into and
out of SQLite via [SQLx](https://github.com/launchbadge/sqlx), and for generally
serializing/deserializing with [Serde](https://serde.rs/), via the `sqlx` and `serde` features,
respectively. One final default optional feature, `chrono`, uses the Chrono crate to return the
timestamp as a [`DateTime`](https://docs.rs/chrono/latest/chrono/struct.DateTime.html) by adding a
`created_at(&self)` method to `Julid`.
Something to note: don't enable the `plugin` feature in your Cargo.toml if you're using this crate
inside your Rust application, *especially* if you're also loading it as an extension in SQLite in
your application. You'll get a long and confusing runtime panic due to there being multiple
entrypoints defined with the same name.
## Safety
There is one `unsafe fn` in this project, `sqlite_julid_init()`, and it is only built for the
`plugin` feature. The reason for it is that it's interacting with foreign code (SQLite itself) via
the C interface, which is inherently unsafe. If you are not building the plugin, there is no
`unsafe` code.
# Why Julids?
The astute may note that this is the third time I've written recently about globally unique sortable
IDs ([here is part one](/rnd/one-part-serialized-mystery), and [part two is
here](/rnd/one-part-serialized-mystery-part-2)). What's, uh... what's up with that?
![marge just thinks they're neat][marge ids]
<div class = "caption">we both just think they're neat</div>
Like Marge says, I just think they're neat! I'm not the only one; here are just some alternatives:
* Segment's [KSUID](https://segment.com/blog/a-brief-history-of-the-uuid/), released in 2017. This
was possibly my first exposure to this idea. They're 36 bits larger than UUIDs or ULIDs, but
otherwise very similar to ULIDs (and hence Julids)
* [ULIDs](https://github.com/ulid/spec), as previously discussed at length
* [UUIDv7](https://www.ietf.org/archive/id/draft-peabody-dispatch-new-uuid-format-01.html#name-uuidv7-layout-and-bit-order);
these are *very* similar to Julids; the primary difference is that the lower 62 bits are left up
to the implementation, rather than always containing pseudorandom bits as in Julids (which use
the lower 64 bits for that, instead of UUIDv7's 62)
* [Snowflake ID](https://en.wikipedia.org/wiki/Snowflake_ID), developed by Twitter in 2010; these
are 63-bit identifiers (so they fit in a signed 64-bit number), where the top 41 bits are a
millisecond timestamp, the next 10 bits are a machine identifier[^twitter machine count], and the last 12 bits are for an
intra-millisecond sequence counter (what Julid calls a "monotonic counter")
and I'm sure the list can go on.
As for what I wanted them for, I wanted to use them in my Rust and SQLite-based [web
app](https://gitlab.com/nebkor/ww), in order to fix some deficiencies in ULIDs, as discussed. Now I
have no unshaved yaks to distract me from getting back to that.
So, is this the last I'll time I'll be writing at length about these things? It's hard to say for
sure, but signs point to "yes". I hope you've found them at least a little interesting!
# Thanks
This crate wouldn't have been possible without a lot of inspiration (and a little shameless
stealing) from the [ulid-rs](https://github.com/dylanhart/ulid-rs) crate. For the loadable
extension, the [sqlite-loadable-rs](https://github.com/asg017/sqlite-loadable-rs) crate made it
*extremely* easy to write; what I thought would take a couple days instead took a couple
hours. Thank you, authors of those crates! Feel free to steal from this project!
----
[^monotonic]: At least, they will still have a total order if they're all generated within the same
process in the same way; the crate and extension use an atomic u64 to ensure that IDs generated
within the same millisecond have incremented counters, but that atomic counter is not global, so
calling `Julid::new()` in Rust and `select julid_new()` in SQLite will not be aware of each
others' counters.
[^my computer]: According to the output of `lscpu`, my computer is an "AMD Ryzen 9 3900X 12-Core
Processor", running between 2.2 and 4.6 GHz. It's no slouch!
[^twitter machine count]: There are only ten bits for the machine ID, which means there are only
1,024 possible machine IDs; did twitter only have a thousand machines in production? Maybe only
a thousand at a time, so you could use the timestamp to look up what machine any given 10-bit ID
referred to?
[marge ids]: ./marge_thinks_theyre_neat.png "marge simpson holding a potato labeled 'globally unique sortable identifiers'"