# M3.8.3 — Compression Benchmarks & Tuning

| Field | Value |
|---|---|
| Phase | M3.8 — Context optimization |
| Size | M — 1 day |
| Status | ⬜ Not started |
| Depends | M3.8.1, M3.8.2 |
| Blocks | M3.8.4 |

## Goal

Measure compression performance across content types and validate that ratios
meet targets without sacrificing quality.

## Deliverables

### 1. Benchmark Suite

New module: `crates/mem-core/src/optimizer/bench.rs` (100 LOC)

```rust
pub fn benchmark_all_compressors() -> BenchmarkReport {
    // Real-world test fixtures:
    // - logs/npm-error.txt (5KB)
    // - logs/cargo-fail.txt (8KB)
    // - json/array-100.json (15KB)
    // - diff/patch-large.diff (10KB)
    // - text/prose-1000words.txt (6KB)
    
    // Measure per-compressor:
    // - compression ratio (%)
    // - time taken (µs)
    // - tokens before/after
}
```

Tests (4):
- `test_log_compression_meets_target` (85-95%)
- `test_json_compression_meets_target` (70-90%)
- `test_diff_compression_meets_target` (60-80%)
- `test_text_compression_meets_target` (30-50%)

### 2. Performance Profile

Command:
```bash
cargo test --release --lib optimizer::bench 2>&1 | grep "time:"
```

Expected output:
```
log compression: 89% ratio, 1.2ms
json compression: 78% ratio, 2.1ms
diff compression: 64% ratio, 1.5ms
text compression: 38% ratio, 1.8ms
```

### 3. Tuning Knobs

Document per-compressor parameters:
- LogCompressor: error line threshold (currently: any line with "error", "failed", etc.)
- JsonCrusher: importance budget (currently: 55%)
- DiffCompressor: context lines kept (currently: 0)
- TextCompressor: token retention ratio (currently: 40%)

## Acceptance

- All 4 compression targets met (measured >= target)
- All benchmark tests passing
- Performance < 3ms per chunk
- Documentation of tuning parameters