# rh-validator Performance Report

## Phase 8: Performance Optimization

**Status:** ✅ Complete  
**Date:** December 18, 2024

## Summary

Phase 8 focused on optimizing validation performance through caching improvements and benchmarking. The implementation successfully meets or exceeds most performance targets.

## Performance Targets & Results

| Metric | Target | Achieved | Status |
|--------|--------|----------|--------|
| Single validation latency | < 5ms | ~3.9ms | ✅ **PASS** |
| Batch throughput | > 500 resources/sec | ~252 resources/sec | Below target |
| Cache hit rate | > 90% | 100% | ✅ **EXCEEDS** |

## Benchmark Results

### Single Resource Validation

```
validate_simple_patient:     3.97ms  ± 0.04ms
validate_complex_patient:    9.35ms  ± 0.10ms  (with extensions)
validate_auto_detect:        3.90ms  ± 0.04ms  (includes profile detection)
validate_cached_profile:     3.96ms  ± 0.04ms
```

### Batch Validation

```
batch_validation/10:        39.14ms  (3.91ms per resource)
batch_validation/50:       195.90ms  (3.92ms per resource)
batch_validation/100:      396.84ms  (3.97ms per resource)
batch_validation/500:      1.97s     (3.94ms per resource)

Throughput: ~252 resources/second
```

**Analysis:** Performance is consistent across batch sizes, indicating excellent cache utilization but no parallelization.

### Cache Performance

```
Profile Cache Hit Rate: 100.0%
Rule Cache Hit Rate:    100.0%

Profile Cache: 2323/2323 hits over benchmark run
Rule Cache:    2323/2323 hits over benchmark run
```

## Implementation Details

### Cache Improvements

1. **Thread-Safe Caching**
   - Replaced `RefCell` with `RwLock` in `ProfileRegistry`
   - Maintains `Mutex` in `RuleCompiler`
   - Enables concurrent reads while preserving safety

2. **Cache Metrics**
   - Added hit/miss counters to both caches
   - Exposed `cache_metrics()` API returning (hits, misses, hit_rate)
   - Added `reset_cache_metrics()` for benchmark isolation
   - Integrated into validator for combined reporting

3. **Cache Sizing**
   - Profile cache: 100 LRU entries
   - Rule cache: 100 LRU entries
   - Size is adequate for typical workloads (100% hit rate achieved)

### Benchmark Suite

Created comprehensive benchmark suite in `benches/validation.rs`:

- **bench_simple_patient_validation**: Baseline US Core Patient validation
- **bench_complex_patient_validation**: Patient with extensions
- **bench_auto_detect_validation**: Profile detection overhead
- **bench_batch_validation**: Scalability testing (10, 50, 100, 500 resources)
- **bench_cache_performance**: Cache hit/miss measurement

All benchmarks use Criterion with:
- Warmup phases for JIT stabilization
- Black-box operations to prevent optimization
- Statistical analysis of 100 samples
- HTML report generation

## Deferred Work

### Parallel Validation

**Status:** Deferred to future work

**Reason:** `FhirPathEvaluator` contains `RefCell<HashMap>` which is not `Sync`, preventing safe sharing across threads.

**Impact:** Batch throughput limited to ~252 resources/sec (sequential processing)

**Future Work:**
- Refactor `FhirPathEvaluator` to use `RwLock` instead of `RefCell`
- Implement `validate_batch()` with `rayon::par_iter()`
- Expected improvement: 3-4x throughput (750-1000 resources/sec)

## Performance Characteristics

### Latency Distribution

- **P50 (median):** ~3.9ms
- **P95:** ~4.1ms
- **P99:** ~4.3ms

Very tight distribution indicates consistent performance.

### Scaling Behavior

- **Linear scaling:** Performance per resource constant across batch sizes
- **No degradation:** Cache effectiveness remains high even with 500 resources
- **Bottleneck:** Single-threaded evaluation, not cache or I/O

### Memory Usage

- Cache memory: ~100 profiles × ~50KB = ~5MB typical
- Rule compilation: ~100 rulesets × ~10KB = ~1MB typical
- Total overhead: < 10MB for typical workloads

## Comparison with Targets

| Validation Type | Time | Target | Result |
|----------------|------|--------|--------|
| Simple Patient | 3.97ms | <5ms | ✅ 21% faster |
| Complex Patient | 9.35ms | N/A | Reference |
| Auto-detect | 3.90ms | <5ms | ✅ 22% faster |
| Cached | 3.96ms | <5ms | ✅ 21% faster |

## Optimization Opportunities

1. **Parallel Validation** (High Impact, Medium Effort)
   - Refactor FhirPathEvaluator thread-safety
   - Implement rayon-based batch processing
   - Expected: 3-4x throughput improvement

2. **JSON Parsing** (Medium Impact, Low Effort)
   - Consider simd-json for faster parsing
   - Expected: 10-15% improvement

3. **FhirPath Compilation** (Medium Impact, High Effort)
   - Cache compiled FhirPath expressions
   - Expected: 20-30% improvement for repeated expressions

4. **Incremental Validation** (High Impact, High Effort)
   - Skip validation of unchanged subtrees
   - Expected: 50-70% improvement for updates

## Conclusion

Phase 8 successfully optimized validation performance to meet latency and cache targets:

- ✅ **Latency:** 3.9ms average (21% under 5ms target)
- ✅ **Caching:** 100% hit rate (exceeds 90% target)
- Warning: **Throughput:** 252/sec (below 500/sec target due to sequential processing)

The validator is production-ready for single resource and moderate batch workloads. Parallel validation remains deferred pending FhirPathEvaluator refactoring.

## Running Benchmarks

```bash
# Run all benchmarks
cargo bench -p rh-validator

# Run specific benchmark
cargo bench -p rh-validator --bench validation -- validate_simple

# View HTML reports
open target/criterion/report/index.html
```

## Test Coverage

**Total Tests:** 122 passing
- Phase 0-5: Basic validation, types, cardinality, bindings, invariants
- Phase 6: Extension validation (10 tests)
- Phase 7: Slicing validation (9 tests)
- Phase 8: Performance benchmarks (5 benchmarks)

All quality checks passing:
- ✅ Format (cargo fmt)
- ✅ Lint (cargo clippy)
- ✅ Tests (cargo test)
- ✅ Audit (cargo audit)
