Question 1

How do I generate a ULID in Go with cryptographically secure randomness?

Accepted Answer

Use crypto/rand.Reader as the entropy source with ulid.New. For example, pass it to ensure secure random data, as the README recommends for security-sensitive use cases to prevent predictable IDs.

Question 2

ULID vs UUID: which is better for database primary keys?

Accepted Answer

ULIDs are superior if you need chronological sorting without extra timestamp columns, as they embed timestamps. UUIDs are simpler if sortability isn't required, and they have broader native support in many databases and languages.

Question 3

How to parse a ULID string back to its timestamp in Go?

Accepted Answer

Use ulid.Parse to convert the string to a ULID, then call ulid.Time() to extract the timestamp. The CLI tool also supports parsing with options like --format for different time representations.

Question 4

What are the performance implications of using ULID in high-concurrency apps?

Accepted Answer

Performance varies with entropy sources: crypto/rand is slower but secure, while math/rand is faster but not thread-safe. The README suggests pooling entropy with sync.Pool to reduce lock contention in concurrent scenarios.

Question 5

Is oklog/ulid thread-safe for concurrent ID generation?

Accepted Answer

It depends on the entropy source. The default ulid.Make uses a thread-safe monotonic reader, but custom sources like math/rand.Rand require synchronization, as noted in the documentation to avoid race conditions.

Question 6

How to ensure monotonic ULIDs when generating IDs in the same millisecond?

Accepted Answer

Use ulid.MonotonicEntropy or ulid.LockedMonotonicEntropy with ulid.New, but be aware of caveats like reduced performance or the need for proper locking, as detailed in the library's godoc.

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