Determinism

How deterministic seeding and unique constraint enforcement work.

Determinism

Seedling guarantees that the same schema + generators + seed + count produces identical output every time.

Seeding

When you provide --seed <int>, Seedling uses a ChaCha8-based deterministic PRNG:

• The master seed derives per-column, per-row sub-seeds
• Every generator uses its deterministic sub-seed instead of crypto/rand
• The order of generation is fixed (topological sort is stable)
• Output is byte-identical across runs

seedling generate --count 50000 --seed 42 --output seed.sql
# Run again — output is byte-identical

Random Mode

Without a seed (--seed 0), Seedling uses crypto/rand for true randomness. Each run produces different data.

Unique Constraints

The UniqueTracker enforces UNIQUE constraints during generation:

• Tracks all generated unique column values in memory
• On collision, retries with a new random value
• Falls back to sequential IDs if collisions are too frequent (exhaustion guard)
• For large datasets, a Bloom filter reduces memory usage (pending)

Determinism Contract

Input	Same Output?
Same schema + seed + count	Yes — byte-identical
Different seed	Different data
Different count	Different data (rows added/removed)
--parallel	Different — parallel execution reorders rows
Same input, different Seedling version	Best-effort (may differ if generators change)