# M3.8.3 — Metrics & Monitoring (UPDATED)

| Field | Value |
|---|---|
| Phase | M3.8 — Context optimization |
| Size | M — 1 day |
| Status | ✅ COMPLETE |
| Depends | M3.8.1, M3.8.2 |
| Blocks | M3.8.4 |

## Deliverables Completed

✅ **MetricsCollector** (7 tests)
- Per-project aggregation of OptimizationMetrics
- Merge metrics from multiple optimization runs
- Structured logging via tracing
- Prometheus-compatible export format

✅ **Test Coverage** (7 tests)
- `test_collector_merge_single_project` — Store and retrieve per-project metrics
- `test_collector_merge_multiple_projects` — Aggregate across projects
- `test_collector_merge_aggregates` — Multiple runs per project
- `test_collector_nonexistent_project` — Handle missing project gracefully
- `test_collector_per_compressor_stats` — Track per-compressor breakdowns
- `test_prometheus_export_format` — Valid Prometheus text format
- `test_prometheus_compression_ratio` — Correct ratio calculations

✅ **Prometheus Export**
- Counter: `m3_8_optimization_records_total`
- Gauge: `m3_8_optimization_input_bytes_total`
- Gauge: `m3_8_optimization_output_bytes_total`
- Gauge: `m3_8_optimization_compression_ratio`
- Per-compressor stats with labels

## Integration Pattern

```rust
use mem_ingest::{MetricsCollector, optimize_record_with_metrics, OptimizationMetrics};
use std::sync::{Arc, Mutex};

let optimizer = ContextOptimizer::from_env()?;
let collector = MetricsCollector::new();

for project_id in projects {
    let metrics = Arc::new(Mutex::new(OptimizationMetrics::default()));
    
    for record in source.records() {
        let optimized = optimize_record_with_metrics(
            record,
            &optimizer,
            &metrics,
        )?;
        embed_and_index(&optimized)?;
    }
    
    let final_metrics = metrics.lock().unwrap().clone();
    collector.merge_project(project_id, final_metrics);
}

// Log summary
collector.log_all_projects();

// Export for Prometheus
let prometheus_text = collector.prometheus_export();
http_server.register_metrics_endpoint("/metrics", prometheus_text);
```

## Status

✅ **Complete and Production-Ready**
- All 7 tests passing
- Prometheus format validated
- Ready to integrate into rebuild pipeline