Snowflakes vs. UUIDs: When Twitter's Identifier Scheme Makes Sense

If you're building a high-throughput system, the choice of ID generation strategy can have massive implications for performance, scalability, and maintainability. The most common contenders? The humble UUID and the high-performance Twitter Snowflake.

In this article, we’ll break down what each approach offers, compare them across key dimensions, and help you decide which one fits your system best.

What Are UUIDs?

UUID stands for Universally Unique Identifier. These 128-bit identifiers are designed to be unique across time and space without requiring a central authority.

There are multiple versions of UUIDs:

• UUIDv1: Time-based with MAC address
• UUIDv4: Random-based
• UUIDv7: Time-ordered, combining benefits of v1 and v4 (newer and promising)

Example UUIDv4:

Pros:

• Globally unique without coordination
• Easy to generate in any language
• Great for database sharding and replication

Cons:

• Not sequential (except v7)
• Large size: 36 characters (or 16 bytes binary)
• Poor for indexing or ordering by time

What Are Snowflake IDs?

Developed by Twitter, Snowflake is a 64-bit integer identifier designed to be:

• Unique across distributed systems
• Ordered by generation time
• Compact and efficient

The Snowflake structure (Twitter’s original spec):

Each Snowflake ID represents a timestamp in milliseconds since a custom epoch, plus metadata for the machine and sequence number.

Example Snowflake:

Pros:

• Time-sortable (great for feeds, logs, and streams)
• Compact: 64-bit integer
• High throughput (up to thousands of IDs/sec per node)

Cons:

• Requires coordination for machine IDs
• Time drift issues (system clock needs to be accurate)
• More complex setup than UUIDs

Head-to-Head Comparison

When to Use UUIDs

Go with UUIDs when:

• You don’t need time-ordering
• Your system operates in a decentralized or offline fashion
• Simplicity and portability matter more than performance

Example Use Cases:

• API keys
• Database primary keys (with caution on write amplification)
• IoT device identifiers

When to Use Snowflakes

Snowflakes make sense when:

• You need monotonic ordering (timestamps embedded)
• You're generating lots of IDs per second
• You control infrastructure and can coordinate machine IDs

Example Use Cases:

• Social media feeds
• Event logs and analytics
• Distributed job/task queues

Performance Notes

In systems where indexing and sort order matter, UUIDs can create write hotspots or fragmentation (especially in Postgres or MySQL). Snowflake’s time-sortable nature leads to better write locality and improved index performance.

However, UUIDv7 and ULIDs (Universally Lexicographically Sortable Identifiers) offer some middle ground — giving time-sortable, unique identifiers without Snowflake’s coordination overhead.

What About Clock Skew?

Snowflake’s reliance on timestamps makes it vulnerable to clock skew. If your system clock moves backward, it could break ID uniqueness unless you're compensating with logic or monotonic clocks. UUIDs don’t suffer from this, making them more robust in loosely synchronized environments.

TL;DR Decision Guide

• Need simplicity + decentralization? UUID
• Need ordering + performance? Snowflake
• Want something in between? Look into UUIDv7 or ULIDs

Final Thoughts

Twitter’s Snowflake system is an engineering marvel optimized for scale and performance. UUIDs are battle-tested and offer plug-and-play simplicity. Choose the one that best aligns with your constraints — and remember, there’s no one-size-fits-all in distributed systems.

Got a hybrid workload? Maybe consider combining strategies — UUIDs for internal entities, Snowflakes for event logs. Use the right tool for the job.

Happy ID-ing!