UUID Stories: Tales from the Trenches of Distributed Computing

UUIDs: small strings, big consequences.

They quietly underpin massive systems, stitching together microservices, databases, queues, and logs. When they work, no one notices. When they don’t... you get called at 3am.

Here are some real stories from engineers who danced with UUIDs — and lived to tell the tale.

📉 The Case of the Truncated UUID

> “We stored only the first 8 characters of UUIDs for ‘simplicity’ — until they started colliding.”

A dev at a high-growth fintech startup shared how their logging pipeline truncated UUIDv4s for display and debug convenience. Unfortunately, those shortened IDs were also used in a few downstream systems for matching — and once volume ramped up, they started colliding.

Lesson:

• Never assume 8 characters of a UUID are enough.
• Even uuid[:8] only gives you 32 bits of entropy — collisions become inevitable in big data sets.

🕰️ When Sorting by UUID Broke Pagination

> “We used UUIDv4s as primary keys and tried to paginate by ORDER BY id... It was chaos.”

A team building a REST API for a document archive used UUIDv4s as primary keys. Later, they added pagination using ORDER BY id ASC LIMIT 50 OFFSET N. But UUIDv4s are completely random — which meant pagination behaved unpredictably. Sometimes it skipped records. Sometimes it duplicated them.

Lesson:

• UUIDv4 ≠ time-ordered
• Use UUIDv7, ULID, or a separate timestamp column if sort order matters

🔍 The Debugging Gold of UUIDs in Logs

> “One UUID led us to a race condition that had been haunting us for weeks.”

An engineer from a SaaS observability platform praised the power of UUIDs in tracing. They tagged each request with a UUID and logged it throughout the service chain. When a rare bug triggered, they found one UUID appeared twice... at the same time... on two threads.

It turned out to be a forgotten shared object reused between goroutines — caught thanks to an "impossible" UUID duplication.

Lesson:

• Use UUIDs as trace or correlation IDs — they can highlight concurrency issues others can't.

💥 The Ghost in the Hash Table

> “We had a mysterious 'collision' every few million UUIDs... until we realized it wasn’t the UUID.”

One dev running a massive test on UUIDv4 uniqueness started seeing “duplicate entries” after generating millions of UUIDs. Panic set in — was UUIDv4 flawed?

Nope.

They were comparing str(uuid.uuid4()) with a slightly transformed version from another service — and string formatting issues were causing false matches. Same UUID bytes, different formatting.

Lesson:

• Always normalize UUIDs before comparison
• Use .hex, .bytes, or .int consistently across systems

🧪 Testing Woes: Mocking UUIDs Gone Wrong

> “Our test data had 50 users with the same UUID because we forgot to mock properly.”

In a unit test suite, a developer had stubbed UUID generation like this:

It worked... too well. Every test user got the same ID, which led to weird DB constraint violations and cascading test failures.

Lesson:

• Always mock UUIDs dynamically, not statically
• Or better: inject UUID generators to control test behavior cleanly

🧯 The Fire That UUIDs Put Out

> “Switching from sequential IDs to UUIDs instantly killed our scraping problem.”

A public API was seeing automated scraping of user records by incrementing IDs. After switching from auto-increment integers to UUIDv4s, the attacks stopped cold. Without the ability to guess the next ID, the scrapers had no easy path forward.

Lesson:

• UUIDs improve security through obscurity
• Not bulletproof, but effective against low-effort attacks

🧠 Honorable Mentions from the Community

• “We used UUIDs for sharding and didn’t realize v4 caused write scattering.”

> Solution: move to v7 or prefixed UUIDs

• “We accidentally stored UUIDs as `VARCHAR(36)` and indexing was *slowww*.”

> Solution: use BINARY(16) or native UUID types when possible

• “UUID collisions? Turns out our load balancer was caching requests.”

> Always check infra before blaming entropy!

🧭 Takeaways

UUIDs are powerful — but power comes with pitfalls. Learn from those who’ve been burned, debugged, and blessed by them:

✅ Best Practices Recap

• Use UUIDv4 for simple, opaque uniqueness
• Use UUIDv7 (or ULID) when sortability matters
• Don’t truncate UUIDs for display or storage
• Normalize UUIDs across services
• Log UUIDs for tracing and debugging
• Use the right format in databases (BINARY > VARCHAR)
• Mock UUIDs carefully in tests

Final Thoughts

Behind every UUID is a story — sometimes heroic, sometimes tragic, often hilarious. They’re more than just unique strings. In the world of distributed systems, UUIDs are glue, guides, and guardians.

Keep them safe, treat them with respect, and never, ever truncate them to save space in your logs.

You’ll thank yourself later. 🧃