Differential Fuzzer

Differential Fuzzer

Always load Debugging skill for reference

The differential fuzzer compares Turso results against SQLite for generated SQL statements to find correctness bugs.

Location

testing/​differential-oracle/​fuzzer/

Running the Fuzzer

Single Run

# Basic run (100 statements, random seed)
cargo run --bin differential_fuzzer

# With specific seed for reproducibility
cargo run --bin differential_fuzzer -- --seed 12345

# More statements with verbose output
cargo run --bin differential_fuzzer -- -n 1000 --verbose

# Keep database files after run (for debugging)
cargo run --bin differential_fuzzer -- --seed 12345 --keep-files

# All options
cargo run --bin differential_fuzzer -- \
  --seed <SEED>           # Deterministic seed
  -n <NUM>                # Number of statements (default: 100)
  -t <NUM>                # Number of tables (default: 2)
  -c <NUM>                # Columns per table (default: 5)
  --verbose               # Print each SQL statement
  --keep-files            # Persist .db files to disk

Continuous Fuzzing (Loop Mode)

# Run forever with random seeds
cargo run --bin differential_fuzzer -- loop

# Run 50 iterations
cargo run --bin differential_fuzzer -- loop 50

Docker Runner (CI/​Production)

# Build and run from repo root
docker build -f testing/​differential-oracle/​fuzzer/​docker-runner/​Dockerfile -t fuzzer .
docker run -e GITHUB_TOKEN=xxx -e SLACK_WEBHOOK_URL=xxx fuzzer

Environment variables for docker-runner:

• TIME_LIMIT_MINUTES - Total runtime (default: 1440 = 24h)
• PER_RUN_TIMEOUT_SECONDS - Per-run timeout (default: 1200 = 20min)
• NUM_STATEMENTS - Statements per run (default: 1000)
• LOG_TO_STDOUT - Print fuzzer output (default: false)
• GITHUB_TOKEN - For auto-filing issues
• SLACK_WEBHOOK_URL - For notifications

Output Files

All output goes to simulator-output/ directory:

Reproducing Errors

Always follow these steps

1. Find the seed in the error output:

   INFO: Starting differential_fuzzer with config: SimConfig { seed: 12345, ... }
   

2. Re-run with that seed:

   cargo run --bin differential_fuzzer -- --seed 12345 --verbose --keep-files
   

3. Check output files:

   • simulator-output/​test.sql - Find the failing statement (look for -- FAILED:)
   • simulator-output/​schema.json - Check table structure at failure time

4. Create a minimal reproducer

   • Create reproducer in .sqltest or in .rs always load Debugging skill for reference

5. Compare behavior manually: If needed try to compare the behaviour and produce a report in the end. Always write to a tmp file first with Edit tool to test the sql and then pass it to the binaries.

   # Run failing SQL against SQLite
   sqlite3 :memory: < simulator-output/​test.sql
   
   # Run against tursodb CLI
   tursodb :memory: < simulator-output/​test.sql
   

Understanding Failures

Oracle Failure Types

1. Row set mismatch - Turso returned different rows than SQLite
2. Turso errored but SQLite succeeded - Turso rejected valid SQL
3. SQLite errored but Turso succeeded - Turso accepted invalid SQL
4. Schema mismatch - Tables/​columns differ after DDL

Warning (non-fatal)

• Unordered LIMIT mismatch - LIMIT without ORDER BY may return different valid rows

Key Source Files

Tracing

Set RUST_LOG for more detailed output:

RUST_LOG=debug cargo run --bin differential_fuzzer -- --seed 12345