UUIDs as Database Primary Keys
Should you use UUID v4 or UUID v7 as a primary key? See how each version affects index locality, and generate sample keys.
Part of the free UUID Generator. Runs in your browser — nothing is uploaded.
UUIDs as Database Primary Keys
Random UUID v4 keys scatter inserts across a B-tree, which can bloat indexes. UUID v7 keeps new rows near the end of the index because the timestamp prefix increases over time. Generate both and pick the one that matches your store.
Worked example: v4 vs v7 for a primary key
Candidates
v4: 550e8400-e29b-41d4-a716-446655440000 v7: 018d5f8a-7c3b-7a21-8f4c-2e9b1a0c5d77
Analysis
✓ Valid UUID Version: 4 — random Variant: RFC 9562 (10xx) ✓ Valid UUID Version: 7 — Unix-epoch time-ordered Variant: RFC 9562 (10xx) Embedded timestamp: 2024-01-31T12:42:07.803Z
Practical tip
In Postgres use the native uuid type, not varchar(36). It stores 16 bytes and compares faster.
How to use this UUID Generator
- 1Use the live tool above — it runs entirely in your browser and never uploads your data.
- 2Paste the sample from the worked example, or use your own input.
- 3Copy the result, then adapt the same steps in your editor, script, or pipeline.
UUIDs as Database Primary Keys FAQs
Is UUID better than a bigserial primary key?
UUIDs are better when IDs must be created in many services without a central counter. Sequential integers are smaller and faster when a single database issues them.
Can I use UUID v4 as a primary key anyway?
Yes, many systems do. Expect more page splits and a larger index than with v7 or a sequence.
More UUID Generator pages
- UUID v4 Generator OnlineGenerate random UUID v4 values online. Cryptographically secure, RFC 4122 / RFC 9562 compatible, free and private in your browser.
- UUID v7 GeneratorGenerate time-ordered UUID v7 values (RFC 9562). Better as database primary keys than random UUID v4 because they sort by creation time.
- GUID Generator OnlineGenerate a GUID online in the Windows {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} format or as a plain UUID. Free, no signup.
- UUID Validator OnlineValidate a UUID or GUID online. Check the 8-4-4-4-12 shape, version nibble and RFC variant, including the Nil UUID.
- Generate a UUID Without HyphensGet a UUID as 32 hex characters with no hyphens. Useful for filenames, tokens and systems that reject the dashed format.
- Bulk UUID GeneratorGenerate many UUIDs at once — up to 1,000 UUID v4 or v7 values. Copy or download the list. Free and browser-based.
- The Nil UUID ExplainedThe Nil UUID is 00000000-0000-0000-0000-000000000000. See when to use it, how validators treat it, and why it is not a random ID.
- Uppercase GUID GeneratorGenerate an uppercase GUID / UUID. Some Windows APIs and .NET codebases expect hex A–F instead of a–f.
- UUID vs GUIDUUID and GUID are the same 128-bit identifier. Learn the naming, formatting differences and how to convert between them.