When Should You Use UUIDs in Databases? Pros, Cons, and Better Alternatives

When designing a database, a common question is how to uniquely identify each row. UUID (Universally Unique Identifier) is a popular choice because it guarantees global uniqueness, but it can also introduce significant performance and storage challenges, especially with large data volumes.

What is a UUID?

A UUID is a 128‑bit number used to uniquely identify objects or records in computer systems. The most common version is UUIDv4, which is generated randomly. An example of a UUIDv4 is:

<code>e942bbe9-afdc-4c62-a438-4efee77954b3</code>

In this example, the 13th digit is "4", indicating it is a UUIDv4. This digit is the key identifier for the UUID version.

UUIDs are especially suitable for scenarios that require a globally unique identifier and can be generated without coordination across different systems, making them ideal for distributed applications. However, using UUIDs as database keys—particularly as primary keys—can bring performance drawbacks.

Problem 1 – Insertion Performance

Most databases use B+ trees to organize indexes for fast lookup. Each time a record is inserted, the B+ tree may need to rebalance to maintain optimal query performance.

If an auto‑increment integer is used as the key, records are inserted sequentially, allowing the database to place them easily in the correct position in the tree. UUIDs, being randomly generated, cause insertion points to be scattered throughout the B+ tree, leading to frequent rebalancing.

When a database grows to millions of rows, this frequent rebalancing can significantly degrade insertion performance.

Problem 2 – Higher Storage Cost

UUIDs are larger than traditional auto‑increment integer keys. The comparison:

Auto‑increment integer: 32 bits per value.

UUID: 128 bits per value.

This means a UUID occupies four times the storage space of an integer! Moreover, many systems store UUIDs in a readable format, which can consume up to 688 bits per value—about 20 times more space than an integer per row.

For tables with millions of rows, using UUIDs can noticeably increase the overall database size.

Performance simulation comparing UUIDs and auto‑increment integers (each table with 1 million rows):

Total table size: the UUID table is roughly 2.3× larger than the integer table.

ID field size: a single UUID field requires about 9.3× the storage of an integer field.

ID column size: the UUID column is about 3.5× larger than the integer column.

These storage differences can significantly affect query performance and the cost of storing large datasets.

Alternatives to UUID

Although UUIDs are widely used, other alternatives may provide better performance and efficiency in certain scenarios:

1. UUIDv7

What it is: a time‑based UUID version that generates identifiers in increasing order.

Why it’s better: because it is time‑based, UUIDv7 retains sequentiality, offering better index performance than the random UUIDv4 while still providing global uniqueness.

Suitable scenarios: when global uniqueness is needed but random insertion would degrade index performance.

2. Auto‑increment Integer

What it is: a sequential number automatically generated by the database for each row.

Why it’s better: its sequential nature makes insertion and indexing highly efficient; it occupies only 32 bits per value and delivers excellent query performance.

Suitable scenarios: small to medium‑sized databases or single‑system applications that do not require global uniqueness.

3. ULID

Universally Unique Lexicographically Sortable Identifier.

What it is: an alternative to UUID that is globally unique and lexicographically sortable.

Why it’s better: ULID uses a time‑stamp prefix followed by a random component, allowing efficient ordered inserts while maintaining global uniqueness.

Suitable scenarios: distributed systems that need UUID‑level uniqueness but where ordering is critical for performance.

When to Use UUID

Despite its drawbacks, UUID remains the best choice in certain cases, especially when global uniqueness is critical. Typical scenarios include:

Distributed systems: multiple nodes or systems generate IDs independently, and UUIDs ensure global uniqueness without coordination.

Merging data from multiple sources: UUIDs prevent record conflicts when consolidating data from different databases or systems.

External exposure: UUIDs are harder to guess or predict than simple integers, providing better security when exposed in URLs or APIs.

However, for single‑system applications or when data does not need to be merged across sources, using auto‑increment integers or time‑based UUID variants (such as UUIDv7 or ULID) is usually a better choice.

Conclusion

While UUIDs provide global uniqueness and are indispensable in distributed systems, their use as database keys can cause significant performance and storage issues, especially with random UUIDv4. If you need sequentiality and better insertion performance, consider UUIDv7 or ULID. For simple applications, auto‑increment integers remain a proven option.

Ultimately, the decision to use UUIDs depends on your system requirements. If global uniqueness is paramount, UUIDs—particularly UUIDv7—remain unmatched. But if performance and storage are your primary concerns, choosing an alternative that fits your use case is wiser.