# Phase 3.2: CI Benchmark Regression Gating

**Status**: Completed
**Date**: 2026-02-05
**Author**: Claude Code

---

## Executive Summary

Implemented automated benchmark regression detection and gating in the CI/CD pipeline. This prevents performance regressions from being merged to main branch by comparing current benchmark metrics against a baseline from the previous successful build.

**Key Capabilities**:
- Automatic metric extraction from Go benchmarks
- Baseline comparison with configurable thresholds
- GitHub Actions integration with detailed reporting
- Three-tier regression detection (Pass / Warning / Critical)

---

## Implementation Overview

### Components

#### 1. Benchmark Comparison Script
**Location**: `/backend/scripts/benchmark-comparison.sh`

Core script that handles:
- Baseline/current metric loading and validation
- Regression percentage calculation
- Report generation (Markdown format)
- GitHub Actions step summary integration
- Three-tier threshold enforcement

**Metrics Tracked**:
- **Response Time**: ns/op (nanoseconds per operation)
- **Memory Usage**: bytes/op and allocs/op (allocations per operation)
- **Throughput**: ops/sec (operations per second, calculated)

**Exit Codes**:
- `0`: Pass (no regression or baseline unavailable)
- `1`: Critical regression (>20%)
- `2`: Reserved for warning-level failures (currently passes with exit 0)

#### 2. CI/CD Integration
**Location**: `.github/workflows/ci.yml`

Added three new steps to the `go-tests` job:

1. **Run Go benchmarks with metrics extraction**
   - Executes benchmarks: `go test -bench=. -benchmem -benchstat ./...`
   - Extracts metrics to JSON format
   - Creates baseline metrics file for artifact storage

2. **Download benchmark baseline**
   - Retrieves previous baseline from GitHub artifacts
   - Runs only on pull requests
   - Gracefully continues if baseline doesn't exist (first run)

3. **Benchmark Regression Comparison**
   - Compares current metrics against baseline
   - Runs comparison script with thresholds
   - Reports results to GitHub step summary
   - Fails CI if critical regressions detected

4. **Upload benchmark metrics as artifact**
   - Stores current metrics for next PR comparison
   - Retention: 90 days
   - Enables trend analysis across builds

---

## Technical Details

### Regression Detection Thresholds

| Level | Range | Action | CI Status |
|-------|-------|--------|-----------|
| ✅ **PASS** | < 10% | No action | ✅ Pass |
| ⚠️ **WARN** | 10% - 20% | Report warning | ✅ Pass (currently) |
| 🔴 **CRITICAL** | > 20% | Block merge | ❌ Fail |

### Regression Calculation

```
Regression % = ((Current - Baseline) / Baseline) * 100
```

For response time metrics:
- Positive value = slowdown (regression)
- Negative value = speedup (improvement)

### Benchmark Metrics JSON Format

Current metrics stored as:
```json
[
  {
    "name": "BenchmarkCreateItem",
    "ns_per_op": 1250,
    "bytes_per_op": 600,
    "allocs_per_op": 12,
    "ops_per_sec": 800000
  }
]
```

### Report Generation

Generated reports include:

1. **Summary Table**
   - Count of benchmarks in each tier (Pass/Warn/Critical)
   - Overall status indicator

2. **Detailed Results Table**
   - Benchmark names and metrics
   - Baseline vs current values
   - Regression percentages
   - Status icons (✅/⚠️/🔴)

3. **Metric Breakdown**
   - Response time trends
   - Memory usage changes
   - Allocation count changes

4. **Threshold Reference**
   - Clear documentation of thresholds
   - Status mapping

### GitHub Actions Integration

Reports are automatically added to GitHub Actions step summary via:
```bash
>> $GITHUB_STEP_SUMMARY
```

This makes them visible in:
- PR checks
- Workflow summary page
- Action logs

---

## Usage Examples

### Running Manually

```bash
# Basic comparison
./backend/scripts/benchmark-comparison.sh \
  --baseline /tmp/baseline.json \
  --current /tmp/current.json \
  --output /tmp/report.md

# Custom thresholds
./backend/scripts/benchmark-comparison.sh \
  --baseline baseline.json \
  --current current.json \
  --threshold-warn 15 \
  --threshold-critical 30
```

### CI/CD Pipeline

The script is automatically invoked in GitHub Actions:

```yaml
- name: Benchmark Regression Comparison
  run: |
    bash scripts/benchmark-comparison.sh \
      --baseline /tmp/go-benchmark-baseline.json \
      --current /tmp/benchmark-current.json \
      --output /tmp/benchmark-comparison-report.md
```

---

## Testing

### Test Coverage

Created comprehensive test suite: `/backend/scripts/test-benchmark-comparison.sh`

**Test Scenarios**:

1. **First Run (No Baseline)**
   - Validates graceful handling of missing baseline
   - Ensures current metrics stored for next comparison

2. **Passing Comparison**
   - Tests <10% regression scenarios
   - Verifies exit code 0 and passing status

3. **Warning Regression**
   - Tests 10-20% regression detection
   - Confirms warning status reported correctly

4. **Critical Regression**
   - Tests >20% regression detection
   - Verifies exit code 1 and failure status

5. **Report Generation**
   - Validates Markdown report structure
   - Checks table formatting
   - Confirms all sections present

6. **JSON Validation**
   - Tests baseline and current JSON parsing
   - Validates metric extraction

7. **Metric Calculation**
   - Tests percentage difference calculations
   - Validates mathematical accuracy

### Running Tests

```bash
chmod +x backend/scripts/test-benchmark-comparison.sh
bash backend/scripts/test-benchmark-comparison.sh
```

### Example Test Output

```
✓ First run succeeds (exit code 0)
✓ Passing benchmarks exit with 0
✓ Warning regression doesn't fail CI
✓ Critical regression fails CI
✓ Report file created
✓ Report includes header
✓ Regression calculation correct
```

---

## Monitored Benchmarks

Current suite covers:

### Handler Layer
- `BenchmarkCreateItem` - POST /api/items
- `BenchmarkGetItem` - GET /api/items/:id
- `BenchmarkListItems` - GET /api/items?project_id=...
- `BenchmarkSearch` - POST /api/search
- `BenchmarkCreateLink` - POST /api/links
- `BenchmarkGraphTraversal` - GET /api/graph/traverse/:id

### Concurrency
- `BenchmarkConcurrentReads` - Parallel read operations
- `BenchmarkConcurrentWrites` - Parallel write operations

### Service Layer
- `BenchmarkServiceCreateItem` - Service layer creation
- `BenchmarkServiceGetItemWithCache` - Cached retrieval
- `BenchmarkServiceListItemsWithCache` - Cached listing
- `BenchmarkServiceUpdateItem` - Item updates
- `BenchmarkServiceDeleteItem` - Item deletion
- `BenchmarkCacheHitRatio` - Cache performance
- `BenchmarkServiceGetWithLinks` - Complex queries
- `BenchmarkServiceGetItemStats` - Statistics calculation

---

## Artifact Management

### Baseline Artifact

**Name**: `go-benchmark-baseline`
**Location**: GitHub Actions artifact storage
**Retention**: 90 days
**Contents**: `benchmark-metrics.json`

**Workflow**:
1. Extract metrics from current build
2. Download baseline from previous build (if exists)
3. Compare metrics
4. Store current metrics as baseline for next build

This enables:
- Trend tracking across multiple PRs
- Historical baseline reference
- Automatic baseline updates on main branch

---

## CI/CD Integration Points

### When Benchmarks Run

1. **Every PR**:
   - Download baseline from main branch
   - Run benchmarks
   - Compare against baseline
   - Report results

2. **Main Branch Pushes**:
   - Run benchmarks
   - Store as baseline for next PR
   - No comparison (first run)

### Conditional Execution

- `if: github.event_name == 'pull_request'` - Comparison runs on PRs only
- `continue-on-error: true` - Baseline download failure doesn't block build
- `if: always()` - Artifact upload happens regardless of test outcome

---

## Performance Baseline Metrics

Initial baseline established (representative values):

| Benchmark | Response Time | Memory | Status |
|-----------|---|---|---|
| CreateItem | 1,250 ns/op | 600 B/op | Baseline |
| GetItem | 850 ns/op | 256 B/op | Baseline |
| ListItems | 2,500 ns/op | 1,024 B/op | Baseline |
| Search | 3,100 ns/op | 1,280 B/op | Baseline |
| ServiceCreateItem | 1,500 ns/op | 600 B/op | Baseline |
| ServiceGetWithCache | 450 ns/op | 128 B/op | Baseline |
| ConcurrentReads | 950 ns/op | 300 B/op | Baseline |
| ConcurrentWrites | 1,800 ns/op | 700 B/op | Baseline |

---

## Error Handling

### Graceful Degradation

1. **Missing Baseline**
   - Treated as first run
   - Current metrics stored for next comparison
   - CI passes (no previous baseline to compare)

2. **Invalid JSON**
   - Detected and reported
   - Treated as first run
   - No comparison performed

3. **Missing Metrics**
   - Handled with default values
   - Benchmarks can be missing from either baseline or current
   - Only matched benchmarks are compared

### Failure Modes

| Scenario | Handling | Exit Code |
|----------|----------|-----------|
| Critical regression | Report + fail CI | 1 |
| Warning regression | Report + pass CI | 0 |
| No baseline | Report + pass CI | 0 |
| Invalid data | Treat as first run | 0 |
| Missing script | CI error | 127 |

---

## Future Enhancements

### Planned Improvements

1. **Historical Trending**
   - Store metrics in database
   - Generate trend graphs
   - Detect long-term regressions

2. **Smart Thresholds**
   - Per-benchmark thresholds
   - Seasonal adjustments
   - Variance-based thresholds

3. **Extended Metrics**
   - CPU utilization
   - Memory allocation patterns
   - Cache hit rates

4. **Integration with Python/Frontend**
   - TypeScript/Vitest benchmark tracking
   - Python performance tests
   - Cross-layer regression detection

5. **Comparison Reports**
   - HTML reports with charts
   - Slack/Discord notifications
   - Email summaries for teams

---

## Troubleshooting

### Script Fails in GitHub Actions

**Problem**: `jq: command not found`

**Solution**: jq is pre-installed on GitHub Actions runners. If using custom runner, install with:
```bash
apt-get update && apt-get install -y jq
```

### Benchmarks Don't Run

**Problem**: `go test -bench=.` not finding benchmarks

**Solution**: Verify benchmark functions exist:
- Must be in `*_test.go` files
- Must start with `Benchmark` prefix
- Must take `*testing.B` parameter

### Report Not Generated

**Problem**: Report file empty or missing

**Solution**: Check script permissions and JSON validity:
```bash
chmod +x backend/scripts/benchmark-comparison.sh
jq empty benchmark-metrics.json  # Validate JSON
```

### False Positives (High Variance)

**Problem**: Benchmarks fail due to environment variance

**Solutions**:
1. Increase sample size: `-benchtime=10s`
2. Run multiple times: Add retry logic
3. Adjust thresholds for high-variance benchmarks
4. Use statistical analysis (future enhancement)

---

## Files Modified/Created

### New Files
- `/backend/scripts/benchmark-comparison.sh` - Core comparison logic
- `/backend/scripts/test-benchmark-comparison.sh` - Test suite
- `/docs/reports/PHASE_3_2_BENCHMARK_REGRESSION_GATING.md` - This document

### Modified Files
- `.github/workflows/ci.yml` - Added benchmark comparison steps
  - Added "Run Go benchmarks with metrics extraction" step
  - Added "Download benchmark baseline" step
  - Added "Benchmark Regression Comparison" step
  - Added "Upload benchmark metrics as artifact" step

---

## Metrics and Success Criteria

### Implementation Complete

- ✅ Benchmark comparison script implemented
- ✅ CI/CD integration completed
- ✅ Three-tier threshold system in place
- ✅ GitHub Actions reporting integrated
- ✅ Test suite created and passing
- ✅ Documentation completed

### Quality Standards Met

- ✅ Exit codes properly handled (0 for pass, 1 for critical)
- ✅ Error messages are clear and actionable
- ✅ Reports are formatted for readability
- ✅ JSON validation and error handling
- ✅ Script is idempotent and repeatable
- ✅ No external dependencies beyond jq (available in CI)

---

## References

### Related Tasks
- Phase 3.1: CI coverage regression detection
- Phase 3.3: Branch protection required status checks
- Phase 3.4: Test pyramid verification script
- Phase 3.5: Coverage baseline document

### External Resources
- [Go Testing Package](https://pkg.go.dev/testing)
- [Benchmark Best Practices](https://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go)
- [GitHub Actions Artifacts](https://docs.github.com/en/actions/using-workflows/storing-workflow-data-as-artifacts)

---

## Sign-Off

**Implementation**: Claude Code Agent
**Testing**: Automated test suite + manual validation
**Review Status**: Ready for integration
**Blockers**: None
**Next Steps**:
1. Merge CI workflow updates
2. Monitor first PR to validate artifact flow
3. Adjust thresholds based on real-world variance
4. Plan Phase 3.3 (branch protection) next

---

## Appendix A: Script Help

```bash
$ ./backend/scripts/benchmark-comparison.sh --help
Usage: ./benchmark-comparison.sh [--baseline FILE] [--current FILE] [--output REPORT] [--threshold-warn PCT] [--threshold-critical PCT]

Options:
  --baseline FILE              Path to baseline metrics JSON (default: benchmark-baseline.json)
  --current FILE               Path to current metrics JSON (default: benchmark-current.json)
  --output REPORT              Path to output report file (default: benchmark-comparison-report.md)
  --threshold-warn PCT         Warning threshold percentage (default: 10)
  --threshold-critical PCT     Critical threshold percentage (default: 20)
```

## Appendix B: Example Metrics JSON

```json
[
  {
    "name": "BenchmarkCreateItem",
    "ns_per_op": 1250,
    "bytes_per_op": 600,
    "allocs_per_op": 12,
    "ops_per_sec": 800000
  },
  {
    "name": "BenchmarkGetItem",
    "ns_per_op": 850,
    "bytes_per_op": 256,
    "allocs_per_op": 8,
    "ops_per_sec": 1176470
  }
]
```

## Appendix C: Example Report Output

```markdown
# Benchmark Regression Comparison Report

**Timestamp:** 2026-02-06T00:51:29Z

## Summary

| Category | Count | Status |
|----------|-------|--------|
| ✅ Passed (<10%) | 8 | Good |
| ⚠️ Warning (10-20%) | 1 | Check |
| 🔴 Critical (>20%) | 0 | Fail |

## Detailed Results

| Benchmark | Baseline (ns/op) | Current (ns/op) | Regression | Status |
|-----------|------------------|-----------------|------------|--------|
| BenchmarkCreateItem | 1000 | 1050 | 5% | ✅ PASS |
| BenchmarkGetItem | 500 | 550 | 10% | ⚠️ WARNING |
```
