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Comment by arp242 | Hacker News Reader

For almost all use cases just showing a UUIDv7 or sequential ID is fine. There are a few exceptions, but it's not the common case.

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How would it be fine, e.g. for e commerce which is arguably very large portion of the use cases?

You would be immediately leaking how many orders a day your business is getting with sequential id.

> You would be immediately leaking how many orders a day your business is getting with sequential id.

Which is fine for almost all of them. All brick and mortar stores "leak" this too; it's really not that hard to guess number of orders for most businesses, and it's not really a problem for the overwhelming majority.

And "Hi, this is Martin, I'd like to ask a question about order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" doesn't really work. Neither does "John, did you already pay order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" or "Alice, isn't 2bf8aa01-6f4e-42ae-8635-9648f70a9a05 the same as what we ordered with 7bb027c3-83ea-481a-bb1e-861be18d21ea?"

Especially for order IDs UUIDs are huge PITA because unlike user IDs and other more "internal" IDs, people can and do want to talk about them. You will need some secondary human-friendly unique ID regardless (possibly obfuscated, if you really want to), and if you have that, then why bother giving UUIDs to people?

Best solution is to have a serial identifier internally and a generated ID for external. And yes it shouldn't be a UUID as they are user-hostile, it should be something like 6-10 letters+digits.

There are jurisdictions e.g. Germany in which a consecutive sequence for invoice numbers is a mandatory, legislated requirement (mercifully, gaps are generally permitted, with caveats)

For extra spice, in some places this is legislated as a per-seller sequence, and in others as a per-customer sequence, so there’s no policy you can apply globally, and this once again highlights the separation of concerns between a primary key and a record locator/identifier.

> consecutive sequence for invoice numbers is a mandatory, legislated requirement (mercifully, gaps are generally permitted, with caveats)

That’s surprising. In Denmark gaps are not allowed. You have to account for all invoices and if you have an invoice numbered 50, then you have at least 50 invoices to account for.

It's nice when you change invoicing software, to be able to have gaps. For example, before Stripe is invoice <500 and Stripe invoices have >500. This makes it simple for humans to determine where an invoice may be located during the transition year. Further, it means we can plan the entire switch-over in advance, vs. only knowing the invoice number AFTER the switch-over. This makes a huge difference in internal communications to customer support, because you can let them know how things will operate once the switch is done. If you can't have gaps, you won't know how to tell customer support where to find new/old invoices until after the switch.

In the Netherlands gaps aren’t allowed either, and I’m surprised that it is elsewhere, as that allows to you get rid of unwanted invoices whenever you want.

However you are allowed to have multiple sequences, differentiated through a prefix, but all starting at 0. That’s what we recently did to switch invoice generation tools (we actually still run both of them alongside each other atm).

Of course you could still drop some invoices from the end when you do this, but I guess tax authorities accept that risk.

The prefixes have to be in order though. You cannot start a prefix with A after already using prefix starting with B.

> There are jurisdictions e.g. Germany in which a consecutive sequence for invoice numbers is a mandatory

Same in France. I thought it was a pretty common requirement.

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