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Comment by gavinray | Hacker News Reader

Yeah I recognize the arguments for UUID keys:

  - Avoids people being able to just iterate through records, or to discover roughly how many records of a thing you have
  - Allows you to generate the key before the row is saved

I think I default to auto-increment ID's due to:

  - Familiarity bias
  - They have a temporal aspect to them (IE, I know row with ID 225 was created before row with ID 392, and approximately when they might be created)
  - Easier to read (when you have less than +1,000,000 rows in a table)

I agree and think you're right in that UUID's are probably a better default.

Though you can never find a "definitive" guide/rule online or in the docs unfortunately.

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> They have a temporal aspect to them (IE, I know row with ID 225 was created before row with ID 392, and approximately when they might be created)

UUIDv7 (currently a draft spec[0]) are IDs that can be sorted in the chronological order they were created

In the meantime, ulid[1] and ksuid[2] are popular time-sortable ID schemes, both previously discussed on HN[3]

[0] https://datatracker.ietf.org/doc/html/draft-peabody-dispatch...

[1] https://github.com/ulid/spec

[2] https://github.com/segmentio/ksuid

[3] ulid discussion: https://news.ycombinator.com/item?id=18768909

UUIDv7 discusison: https://news.ycombinator.com/item?id=28088213

Wow, neat. TIL

Hmmm that's really useful :) . thanks!

Yup this. Ulid is great, and implemented in many languages. For example there’s a crate named Ulid that you can use that gives you ulid’s in Rust.

Came here to also hype ULID. It's just like INT, but 128bit, timestamps, every lang, and moving data around is trivial because no ID ever collide with anything else ever. Makes finding crap in my logs easier. (But UUID has that feature too) - it's the sorting that does it for me.

Is there a PostgreSQL extension for ulid?

I never found one. I am really interested in it too, but I bwlieve PG ecosystem will support uuidV7 before considering ulid.

Here's one[1], not actively maintained though.

[1] https://github.com/edoceo/pg-ulid

I had reviewed existing UUIDv7 implementations and many were incorrect or had subtle timing bugs.

We ended up implementing UUIDv7 in our ID generation library https://github.com/MatrixAI/js-id. And we have a number of tests ensuring that it is truly monotonic even across process restarts.

See IdSortable.

Something I always liked but have never done -- start auto-increment IDs at some number other than 1. I worked on a system where account IDs started with 1000000, invoice IDs started with 2000000, etc. That way, if you saw a random number laying around like "1001234", you knew it was an account ID. "2000123", an invoice! I don't remember how often it helped things, but it was more than 0 times, and it always "felt" good. I never loved the implicit upper bound, but it was also never a problem.

(And remember, the values are in different tables, so the only disadvantage is that your millionth user has ID 2000000. To the trained eye they look like an invoice; but there is no way for the system itself to treat that as an invoice, so it's only confusing to humans. If you use auto-increment keys that start at 1, you have the same problem. Account 1 and Invoice 1 are obviously different things.)

> but there is no way for the system itself to treat that as an invoice, so it's only confusing to humans.

I agree in principle, but then you have Windows skipping version 9 because of all of the `version.hasPrefix("9")` out in the world that were trying to cleverly handle both 95 and 98 at once. If a feature of data is exploitable, there's a strong chance it will be exploited.

I use this for internal items, as in: real customer IDs start at 10,000, so we have 9,999 possible users/invoices/whatever for our own usage in the database. That makes it easy to filter demo accounts of your sales employees, or production test accounts, in queries: just add an offset.

Re: the upper bound: if you reach a million customers, you have lots of other nice problems, like how to spend all the money they earn you :-)

This is clever.

You could use "is_test_account" or whatnot, but that adds an unnecessary column (for ~99% of records)

I like this -- will keep it in mind!

I worked on an existing database once that stored geographic locations and used the signed bit for namespacing.

Positive IDs were home-grown, negative ones were Unique Feature Identifiers from some old GNS system import (from some ancient US Government/Military dataset).

Then when something had to be edited/replaced/created it would possibly change a previously negative ID to positive, fun times.

I’ve seen systems that had to track only two types of things - one started at half the value and went up; the other started just below that and went down. Think 500000+ vs 499999-

I prefer UUIDs as well but one other benefit of an integer type key is in the index. UUIDs, especially v4, make for bloated indexes. If there’s a very specific performance reason I’ll use int, otherwise uuid.

This is what I do as well. Most schema structure is on tables that are not very large, and it's nice especially when dealing with multiple environments to prevent errors, or to produce schemas with some polymorphism or joins between several tables without a chain of id-resolving joins in-between.

There are UUID variants that can work well with indices, which shrinks the case for big-integers yet further, to micro-optimizing cases that are situational.

You can use sequential guids. That's what I do. Works well for not bloating indices.

One of hidden pros is that UUID has no gaps visible to product owner or manager. More than once in my life I have try convince people, that the gap in sequence caused by transaction rollback is OK. Several times we were «fixing data» in db manually

The person you're replying to didn't even mention those advantages though! The ones they did mention are more significant to me.

Of your disadvantages... if I wanted to know when rows were created, I'd just add a created timestamp column.

But "easier to read" is for real -- it's easy when debugging something to have notes referencing rows 12455 and 98923823 or in some cases even keep them in your head. But UUIDs are right out.

And you definitely don't want to put UUIDs in a user-facing URL -- which is actually how you get around "avoids people being able to just iterate through records", really whether you have UUIDs or numeric pks I think putting internal PK's in URLs or anything else publicly exposed is a bad idea, just keep your pks purely internal. Once you commit to that, the comparison between UUIDs vs numeric as pks changes again.

> I think putting internal PK's in URLs or anything else publicly exposed is a bad idea

Why?

Both as a user and as a dev I love that I can just change the PK to get to a specific post, item, whatever instead of changing the whole link.

I mean, the links are going to be a template either way, so you can change the identifier part to change the item; it's just a question of whether the identifier portion is the internal rdbms PK, or something else.

It's considered undesirable because it's basically an "implementation detail", it's good to let the internal PK change without having to change the public-facing URLs, or sometimes vice versa, when there are business reasons to do so.

And then there are the at least possible security implications (mainly "enumeration attacks") and/or "business intelligence to your competitors" implications too.

But it's true that plenty of sites seem to expose the internal PK too, it's not a complete consensus. Just kind of a principle to separate internal implementation from public interface.

Here's a short 2008 HN discussion on it, in which people have both opinions: https://news.ycombinator.com/item?id=19876901

Here's a more recent and lengthy treatment:

https://czep.net/21/obfuscate.html

Thanks, especially those links are helpful, will read through it :)

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