# Performance Audit Report

**Branch**: fix/issue-28-graph-corruption-shallow-copy
**Base**: main
**Date**: 2025-11-28 11:04
**Files Analyzed**: 11
**Lines Changed**: 357 insertions, 97 deletions

---

## Summary of Changes Reviewed

1. **src/core/dependency-graph.ts** - Deep copy fix in `wouldCreateCycle()` (lines 249-255)
2. **src/implementations/resource-monitor.ts** - Settling workers tracking (lines 27-181)
3. **src/core/configuration.ts** - `minSpawnDelayMs` changed from 50ms to 1000ms (lines 32, 69)

---

## [RED CIRCLE] Performance Issues in Your Changes (BLOCKING if Severe)

### MEDIUM

**Deep Copy Overhead in wouldCreateCycle()** - `/workspace/delegate/src/core/dependency-graph.ts:253-255` (line ADDED in this branch)

- **Problem**: Deep copy creates new Map and new Set for every entry on each cycle check
- **Impact**: O(N) memory allocation where N = number of nodes in graph
- **Code**:
  ```typescript
  const tempGraph = new Map(
    Array.from(this.graph.entries()).map(([k, v]) => [k, new Set(v)])
  );
  ```
- **Analysis**: 
  - Previous shallow copy: O(1) Map creation (Set references shared)
  - New deep copy: O(N) Map creation + O(E) Set element copies
  - For graph with 100 tasks and average 2 dependencies each: ~100 Set allocations + ~200 element copies
- **Real-World Impact**: MINIMAL
  - Cycle detection runs once per dependency addition, not in hot path
  - Typical dependency graph is small (<100 tasks)
  - Correctness trumps micro-optimization (shallow copy caused CRITICAL bug)
- **Recommendation**: ACCEPTABLE TRADE-OFF - correctness fix outweighs performance cost
- **Expected overhead**: ~0.1ms per cycle check for typical graphs (negligible)

**Verdict**: NOT BLOCKING - This is the correct fix for a critical bug. The performance cost is acceptable.

---

### LOW

**Array.from() Intermediate Allocation** - `/workspace/delegate/src/core/dependency-graph.ts:253`

- **Problem**: `Array.from()` creates intermediate array before Map construction
- **Impact**: Extra O(N) memory allocation for intermediate array
- **Alternative**: Could use iterator-based approach
  ```typescript
  const tempGraph = new Map<string, Set<string>>();
  for (const [k, v] of this.graph) {
    tempGraph.set(k, new Set(v));
  }
  ```
- **Expected improvement**: ~10-20% faster for large graphs, eliminates intermediate allocation
- **Recommendation**: OPTIONAL optimization if this becomes a hot path

---

## [YELLOW WARNING] Performance Issues in Code You Touched (Should Optimize)

### MEDIUM

**Array Filter on Every canSpawnWorker() Call** - `/workspace/delegate/src/implementations/resource-monitor.ts:82-84` (line ADDED in this branch)

- **Problem**: `recentSpawnTimestamps.filter()` creates new array on every spawn check
- **Impact**: O(N) array allocation where N = number of recent spawns
- **Code**:
  ```typescript
  this.recentSpawnTimestamps = this.recentSpawnTimestamps.filter(
    t => now - t < this.SETTLING_WINDOW_MS
  );
  ```
- **Analysis**:
  - `canSpawnWorker()` is called every 5 seconds (resourceMonitorIntervalMs)
  - Maximum settling workers likely <10 (15s window / spawn rate)
  - Array is small, allocation is cheap
- **Real-World Impact**: NEGLIGIBLE
  - Typical array size: 0-5 elements
  - Called at most every 5 seconds (not a hot path)
- **Better Alternative** (if this becomes a hot path):
  ```typescript
  // In-place cleanup without allocation
  let writeIndex = 0;
  for (let i = 0; i < this.recentSpawnTimestamps.length; i++) {
    if (now - this.recentSpawnTimestamps[i] < this.SETTLING_WINDOW_MS) {
      this.recentSpawnTimestamps[writeIndex++] = this.recentSpawnTimestamps[i];
    }
  }
  this.recentSpawnTimestamps.length = writeIndex;
  ```
- **Recommendation**: OPTIONAL - current implementation is fine for expected usage

---

### LOW

**minSpawnDelayMs Increased from 50ms to 1000ms** - `/workspace/delegate/src/core/configuration.ts:32` (line MODIFIED)

- **Problem**: 20x increase in minimum spawn delay
- **Impact**: Reduced task throughput during burst scenarios
- **Analysis**:
  - Old: Could spawn 20 workers/second in theory
  - New: Maximum 1 worker/second
  - For 10 queued tasks: 10s minimum delay vs 0.5s
- **Justification in PR**: Works with settling worker tracking to prevent spawn burst overload
- **Trade-off**: Throughput vs Stability
  - Better: Prevents system overload from rapid spawning
  - Worse: Slower task execution during high-demand periods
- **Recommendation**: ACCEPTABLE - stability is more important than throughput
- **Configuration**: Can be overridden via `WORKER_MIN_SPAWN_DELAY_MS` env var

---

## [INFO CIRCLE] Pre-existing Performance Issues (Not Blocking)

### MEDIUM

**DFS Cycle Detection Creates Multiple Sets** - `/workspace/delegate/src/core/dependency-graph.ts:270-271` (pre-existing)

- **Problem**: `visited` and `recursionStack` Sets created on every cycle check
- **Context**: This existed before your changes
- **Recommendation**: Consider pooling or reusing Sets in high-throughput scenarios
- **Reason not blocking**: Part of original algorithm, not introduced by this PR

---

### LOW

**Multiple os.cpus() Calls** - `/workspace/delegate/src/implementations/resource-monitor.ts:106,185` (pre-existing)

- **Problem**: `os.cpus()` called multiple times in same operation
- **Context**: Existed before your changes
- **Recommendation**: Cache CPU count in constructor (CPU count rarely changes)
- **Reason not blocking**: Pre-existing, minor impact

---

### LOW

**Load Average-Based CPU Calculation** - `/workspace/delegate/src/implementations/resource-monitor.ts:305-318` (pre-existing)

- **Problem**: Load average is a lagging indicator (1-minute rolling average)
- **Context**: Your settling worker tracking helps address this
- **Recommendation**: Consider instant CPU sampling for more responsive scaling
- **Reason not blocking**: Pre-existing design decision, settling tracking mitigates

---

## Performance Characteristics of New Code

### Deep Copy Analysis (dependency-graph.ts)

| Graph Size | Shallow Copy | Deep Copy | Overhead |
|------------|--------------|-----------|----------|
| 10 tasks   | ~0.01ms      | ~0.02ms   | +0.01ms  |
| 100 tasks  | ~0.01ms      | ~0.1ms    | +0.09ms  |
| 1000 tasks | ~0.01ms      | ~1ms      | +0.99ms  |

**Note**: These are estimated values. Actual performance depends on JavaScript engine, memory pressure, and Set sizes.

### Settling Workers Tracking Analysis (resource-monitor.ts)

| Operation | Complexity | Frequency | Impact |
|-----------|------------|-----------|--------|
| recordSpawn() | O(1) | Per spawn | Negligible |
| cleanup filter | O(N) | Every 5s | N<10 typical |
| projectedCoresUsed | O(1) | Every 5s | Negligible |
| projectedMemoryUsed | O(1) | Every 5s | Negligible |

---

## Summary

**Your Changes:**
- [RED CIRCLE] CRITICAL: 0
- [RED CIRCLE] HIGH: 0
- [RED CIRCLE] MEDIUM: 1 (Deep copy overhead - ACCEPTABLE for correctness)
- [RED CIRCLE] LOW: 1 (Array.from intermediate allocation)

**Code You Touched:**
- [YELLOW WARNING] HIGH: 0
- [YELLOW WARNING] MEDIUM: 1 (Array filter allocation)
- [YELLOW WARNING] LOW: 1 (minSpawnDelayMs throughput trade-off)

**Pre-existing:**
- [INFO CIRCLE] MEDIUM: 1 (DFS Set allocations)
- [INFO CIRCLE] LOW: 2 (os.cpus() calls, load average design)

**Performance Score**: 8/10

**Merge Recommendation**:
[GREEN CHECK] APPROVED - The performance impact is minimal and acceptable:

1. **Deep copy fix** is necessary for correctness. The shallow copy bug caused graph corruption which is far worse than any performance overhead.

2. **Settling workers tracking** adds negligible overhead (~0.01ms per spawn check) while preventing spawn burst overload.

3. **minSpawnDelayMs increase** trades throughput for stability - a reasonable choice for a worker orchestration system.

4. All identified performance issues are:
   - Either acceptable trade-offs for correctness/stability
   - Or too minor to warrant blocking this PR

---

## Optimization Priority

**Fix before merge:**
- None required

**Optimize while you're here (OPTIONAL):**
1. Replace `Array.from().map()` with for-of loop in deep copy (minor optimization)

**Future work:**
- Monitor cycle detection performance if task count grows significantly
- Consider CPU count caching in ResourceMonitor constructor
- Profile actual performance in production to validate estimates

---

*Report generated for performance audit of fix/issue-28-graph-corruption-shallow-copy branch*
