Self-Hosted Unique ID Generation Libraries: Snowflake vs ULID vs KSUID vs XID

Every distributed system needs to generate unique identifiers. Whether it’s database primary keys, event IDs in a message queue, request tracing spans, or object keys in blob storage — the choice of ID generation strategy has far-reaching consequences for database performance, sortability, and debugging experience.

Auto-incrementing integers work fine in a single database, but in a distributed system with multiple writers across regions, you need globally unique IDs without coordination. This article compares four popular open-source unique ID generation libraries: Snowflake (Twitter’s classic), ULID (Universally Unique Lexicographically Sortable Identifier), KSUID (Segment’s K-Sortable Unique ID), and XID (globally unique ID for the web).

Why Unique ID Generation Matters

Database B-tree indexes perform best with monotonically increasing keys. Random UUIDs cause page splits and index fragmentation, degrading write performance by 30-50% in high-throughput scenarios. Sortable IDs solve this — they’re roughly ordered by creation time, keeping indexes compact while maintaining global uniqueness.

For distributed systems, see our guides on distributed locking and distributed key-value stores.

Comparison Table

Twitter Snowflake: The Original

Snowflake is a network service that generates 64-bit unique IDs. It coordinates worker IDs via ZooKeeper and produces IDs that are roughly time-ordered. Snowflake was designed for Twitter’s scale — hundreds of thousands of IDs per second per machine.

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# Docker Compose for Snowflake ID service
version: "3.8"
services:
  snowflake:
    image: snowflake-server:latest
    ports:
      - "8080:8080"
    environment:
      SNOWFLAKE_DATACENTER_ID: "1"
      SNOWFLAKE_WORKER_ID: "1"
      SNOWFLAKE_ZK_CONNECT: "zookeeper:2181"
    depends_on:
      - zookeeper

  zookeeper:
    image: zookeeper:3.8
    ports:
      - "2181:2181"

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// Snowflake ID usage (via REST API)
SnowflakeClient client = new SnowflakeClient("http://snowflake:8080");
long messageId = client.nextId();      // 1358700049549852673
long eventId = client.nextId();        // 1358700049549852674

Key strengths: Time-tested at Twitter scale, compact 8-byte integers (ideal for MySQL/Postgres bigint primary keys), and guaranteed uniqueness within a datacenter. Drawbacks: Requires ZooKeeper for worker coordination, is network-dependent (adds latency), and the original Scala service is no longer actively maintained (archived by Twitter).

ULID: UUID Compatibility with Sortability

ULID (Universally Unique Lexicographically Sortable Identifier) is a specification, not a service — implementations exist in 50+ languages. ULIDs are 128-bit values (like UUIDs) but are lexicographically sortable because the timestamp comes first.

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# Python ULID generation
from ulid import ULID

ulid = ULID()
id1 = str(ulid.generate())   # "01ARZ3NDEKTSV4RRFFQ69G5FAV"
id2 = str(ulid.generate())   # "01ARZ3NEW0CYPHJZXQSTCBPEWW"

# ULIDs sort correctly by time
assert id1 < id2  # True! id1 was generated first

# Binary representation fits in UUID column
binary = ulid.generate().bytes  # 16 bytes

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-- PostgreSQL: Use ULID as primary key
CREATE TABLE events (
    id BYTEA PRIMARY KEY DEFAULT gen_random_bytes(16),
    payload JSONB,
    created_at TIMESTAMPTZ DEFAULT now()
);

-- Sorted scan still works!
SELECT * FROM events ORDER BY id DESC LIMIT 50;

Key strengths: UUID compatibility (fits in existing UUID columns), sortable by creation time, no coordination required, and 50+ language implementations. The 26-character Crockford base32 string representation is URL-safe and human-readable.

KSUID: Segment’s K-Sortable Unique ID

KSUID (K-Sortable Unique ID) takes a different approach: a 32-bit second-precision timestamp combined with 128 bits of random payload, totaling 20 bytes. The “K-sortable” property means IDs sort roughly by time even across different generators — ideal for distributed systems with independent ID generation.

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// Go KSUID generation
import "github.com/segmentio/ksuid"

id1 := ksuid.New()   // "0o5HrWjJRBuRXKfZDmHOSW1Ppcd"
id2 := ksuid.New()   // "0o5HrWk8xBxHnPjWNPhnFGbNeqL"

// Parse and extract timestamp
parsed, _ := ksuid.Parse(id1.String())
fmt.Println(parsed.Time())  // 2026-06-21 06:15:43 +0000 UTC

// Compare IDs
fmt.Println(ksuid.Compare(id1, id2))  // -1 (id1 < id2)

Key strengths: Largest random payload (128 bits) of any sortable ID — virtually zero collision probability; extractable timestamp without decoding; base62 encoding is URL-safe; and the reference Go implementation is battle-tested at Segment’s scale.

XID: Globally Unique ID for the Web

XID takes a pragmatic approach: combine the machine’s hostname hash, process ID, and an atomic counter to achieve global uniqueness without coordination. At 12 bytes, it’s more compact than ULID, UUID, or KSUID.

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// Go XID generation
import "github.com/rs/xid"

id := xid.New()

fmt.Println(id.String())         // "9m4e2mr0ui3e8a215n4g"
fmt.Println(id.Time())           // 2026-06-21 06:15:43.123 +0000 UTC
fmt.Println(id.Machine())        // [186, 162, 175, 159, 199]
fmt.Println(id.Pid())            // 12345
fmt.Println(id.Counter())        // 4271903

// Binary representation (12 bytes)
binary := id.Bytes()

Key strengths: Compact 12-byte format (vs 16 for ULID, 20 for KSUID), no network coordination, embedded machine fingerprint for debugging, and an atomic counter that guarantees uniqueness per process. The 20-character string representation is URL-safe.

Why Self-Host Your ID Generation?

Using a self-hosted ID generation library — rather than relying on database auto-increment or a cloud service — offers several advantages:

Database portability — Your IDs are independent of your database. Migrate from PostgreSQL to CockroachDB without changing your ID scheme.

Multi-region writes — Generate IDs in multiple regions without coordination. ULID, KSUID, and XID require zero coordination between generators.

Performance — Local ID generation is sub-microsecond. A network round-trip to a Snowflake service or database nextval() adds milliseconds to every insert.

Human-readable timestamps — ULID and KSUID encode the creation time in the ID itself. Debugging becomes trivial: you can see when an object was created just by looking at its ID, without querying a database.

For more on distributed system design patterns, see our distributed transactions guide and our hash function libraries comparison.

Choosing the Right ID Library

• MySQL/Postgres bigint primary keys: Snowflake (8-byte integers are ideal)
• UUID column compatibility + sortability: ULID (fits in UUID columns, 50+ language implementations)
• Maximum collision resistance: KSUID (128-bit random payload, virtually zero collision risk)
• Minimal storage footprint: XID (12 bytes, 20-character strings)
• Zero infrastructure: ULID, KSUID, or XID (all library-only, no server needed)
• Need to extract timestamps from IDs: KSUID or XID (built-in timestamp extraction)

FAQ

Can I use ULIDs as PostgreSQL primary keys?

Yes — ULIDs are 16 bytes, same as UUIDs. Use a BYTEA column for binary storage or a VARCHAR(26) for the string representation. PostgreSQL 17+ has native ULID support. A B-tree index on ULIDs performs much better than on random UUIDv4 because ULIDs are roughly insertion-ordered.

What happens if two ULIDs are generated at the same millisecond?

ULID uses an 80-bit random component. At the same millisecond, the probability of collision is 1 in 2^80 (approximately 1 in 1.2 septillion). For comparison, you’d need to generate 1 billion ULIDs per millisecond for 40 years to have a 50% chance of a single collision. In practice, this never happens.

Is Snowflake still maintained?

No — Twitter archived the original Snowflake repository in July 2020. However, the Snowflake ID format is a specification that many implementations support, including Discord’s implementation, Baidu’s UID-Generator, and the Leaf project from Meituan-Dianping. For new projects, ULID or KSUID are better choices unless you specifically need 64-bit integer IDs.

How do I migrate from auto-increment IDs to sortable IDs?

Migrate incrementally: (1) Add a new ULID or KSUID column alongside your existing id column. (2) Write both IDs in new records, generating ULIDs for existing records. (3) Update foreign key references to use the new column. (4) Eventually drop the auto-increment column. The dual-write period can last as long as needed — there’s no downtime required.

Which ID format is best for URL path segments?

XID and ULID are the most URL-friendly. XID produces 20-character strings like 9m4e2mr0ui3e8a215n4g, and ULID produces 26-character strings like 01ARZ3NDEKTSV4RRFFQ69G5FAV. Both use URL-safe character sets (no /, +, or =). KSUID’s 27-character base62 strings are also URL-safe. Snowflake’s numeric IDs are shorter but reveal information about your ID generation rate.

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