You let users generate a UUID?
replyTo be honest, the chance that you are doing something weird is probably higher than you experiencing a real UUID conflict.
How did your database 'flag' that conflict?
user-generated (as in: on the user's phone) was only at the very early stages of this product, and we've since moved to on-server. It's a cash-register type of app, where the same invoice must not be stored twice. So we used to generate a fresh invoice_id (uuidv4) on the user's device for each new invoice, and a double-send of that would automatically be flagged server-side (same id twice). This has since moved on to a server-only mechanism.
replyThe database flagged it simply by having a UNIQUE key on the invoice_id column. First entry was from 2025, second entry from today.
The UUIDv4 collision is statistically extremely unlikely. What is more likely is both systems used the same seed. This might be just a handful of bytes, increasing the chance of collision to one in billions or even millions.
replyBetter check what crypto.js is actually doing in your exact setup. Weak polyfills exist...
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