The website appears to date from 2008. This was a _very_ common latent bug at that point, particularly because Rails would basically force you to implement it. I assume this got fixed at some point, but for a long time all ActiveRecord models had an autoincrementing ID, which had to be a signed 32 bit int. There were scary monkey-patching workarounds if you wanted something more sensible.

EDIT: And, yes, it is apparently Rails! https://fanlore.org/wiki/Archive_of_Our_Own#Timeline

Nah I made the same mistake back in 2009 for a system that was storing behavior events during malware analysis.

You don’t often expect to have two billion of something until you do.

Salesforce is a rather popular platform.

Its defaults are also either a 18-character ID, or a 32bit integer. So, unless you take the effort to actually fight Apex, you're gonna hit this problem sooner or later.

One of the first things I internalized about databases was "just always use BIGSERIAL for primary keys". There are very few good reasons not to.

or use UUID/GUIDS, many databases (eg PostgreSQL) and frameworks (eg Django) support them.

let's use 128bit integer and handle them like floats in php!

and maybe put a 32bit timestamp along and pretend it can somehow store more than a 32bit integer can.

There's no SLA for Harry Styles porn. Run the migration, lock the table for two days and redo the same in 13 years when you get to 4 billion bookmarks.