Performance Analysis

Performance Analysis & Optimization

Provides performance analysis patterns for runtime, memory, cost optimization, and scalability assessment across code changes and architecture decisions.

Description

This skill teaches performance agents how to analyze code for runtime complexity, memory usage, scalability bottlenecks, and cost implications. It covers Big O analysis, profiling techniques, caching strategies, database optimization, and cloud cost modeling.

When to Use

• Analyzing algorithm complexity and efficiency
• Reviewing database queries and indexes
• Evaluating caching strategies
• Assessing API response times and throughput
• Analyzing memory usage and leaks
• Estimating cloud infrastructure costs
• Planning for scale (10x, 100x traffic growth)

When NOT to Use

• Do not use for functional correctness or business logic review — use the reviewer agent instead.
• Do not use for security vulnerability analysis — use the security-review skill instead.

Entry Points

Trigger Phrases: "performance review", "optimize this code", "check scalability", "analyze runtime", "memory usage", "cost estimate"

Context Patterns: Algorithm implementations, database queries, API endpoints with high traffic, batch processing jobs, resource-intensive operations

Core Knowledge

Big O Complexity Analysis

Database Optimization

Query Performance:

-- ❌ BAD: N+1 queries (100 users = 101 queries)
SELECT * FROM users;
-- For each user: SELECT * FROM orders WHERE user_id = ?

-- ✅ GOOD: Single query with JOIN
SELECT users.*, orders.*
FROM users
LEFT JOIN orders ON users.id = orders.user_id;

-- ❌ BAD: Full table scan
SELECT * FROM orders WHERE status = 'shipped';

-- ✅ GOOD: Index on status column
CREATE INDEX idx_orders_status ON orders(status);
SELECT * FROM orders WHERE status = 'shipped';

Indexing Strategy:

• Primary key: Always indexed automatically
• Foreign keys: Index for JOIN performance
• WHERE clause columns: Index frequently queried fields
• Composite indexes: Order matters (most selective first)

Caching Strategies

Memory Profiling

Common Issues:

• Memory leaks (unreleased resources, event listeners)
• Excessive allocations (unnecessary object creation)
• Large data structures (unbounded caches, result sets)
• Circular references (garbage collection prevention)

Mitigation:

// ❌ BAD: Memory leak (event listener not removed)
class Component {
  constructor() {
    window.addEventListener('resize', this.handleResize);
  }
}

// ✅ GOOD: Cleanup in destructor
class Component {
  constructor() {
    window.addEventListener('resize', this.handleResize);
  }
  destroy() {
    window.removeEventListener('resize', this.handleResize);
  }
}

// ❌ BAD: Unbounded cache
const cache = {};
function get(key) {
  if (!cache[key]) cache[key] = expensiveOperation(key);
  return cache[key];
}

// ✅ GOOD: LRU cache with size limit
const cache = new LRU({ max: 100, maxAge: 60000 });

Cost Optimization (Cloud)

AWS Cost Drivers:

• Compute: EC2, Lambda invocations
• Storage: S3, EBS volumes
• Data transfer: Outbound bandwidth
• Database: RDS, DynamoDB reads/writes

Optimization Patterns:

• Right-sizing: Match instance size to workload
• Reserved instances: 30-70% savings for predictable workloads
• Spot instances: 70-90% savings for fault-tolerant workloads
• S3 Intelligent-Tiering: Auto-move cold data to cheaper tiers
• CloudFront caching: Reduce origin load and bandwidth

Performance Review Template

## Performance Analysis: [Feature]

### Runtime Complexity
- **Current:** O(?) - [Description]
- **Bottleneck:** [Specific operation]
- **Improvement:** O(?) - [Proposed optimization]

### Database Impact
- **Query count:** N queries per request
- **Indexes:** Missing on [columns]
- **Recommendation:** [Add indexes, rewrite query, use caching]

### Memory Usage
- **Peak allocation:** XMB per request
- **Leak risk:** [None / Identified in Y]
- **Recommendation:** [Optimization strategy]

### Scalability Assessment
- **Current capacity:** X req/sec
- **10x traffic:** [Bottleneck analysis]
- **100x traffic:** [Architecture changes needed]

### Cost Impact
- **Monthly estimate:** $X (current) → $Y (after change)
- **Cost drivers:** [Compute, storage, bandwidth]
- **Optimization opportunities:** [List]

### Verdict
- [ ] APPROVED (no performance concerns)
- [ ] MINOR_CONCERNS (acceptable for MVP, optimize later)
- [ ] MAJOR_CONCERNS (blocks deployment, requires optimization)

Examples

Example: Inefficient Algorithm Review

Code:

def find_duplicates(arr):
    duplicates = []
    for i in range(len(arr)):
        for j in range(i+1, len(arr)):
            if arr[i] == arr[j] and arr[i] not in duplicates:
                duplicates.append(arr[i])
    return duplicates

Performance Analysis:

## Performance Analysis: find_duplicates

### Runtime Complexity
- **Current:** O(n²) - Nested loops scan entire array
- **Bottleneck:** Inner loop iterates (n-1) + (n-2) + ... + 1 ≈ n²/2 times
- **Improvement:** O(n) using hash set

### Scalability Impact
| Input Size | Current (O(n²)) | Optimized (O(n)) |
|------------|-----------------|------------------|
| 100 items | 10,000 ops | 100 ops |
| 1,000 items | 1,000,000 ops | 1,000 ops |
| 10,000 items | 100,000,000 ops | 10,000 ops |

**At 10K items:** 10,000x performance improvement

### Memory Usage
- **Current:** O(n) for duplicates list
- **Optimized:** O(n) for seen set + duplicates
- **Trade-off:** Slightly higher memory for massive speed gain

### Recommended Implementation

```python
def find_duplicates(arr):
    seen = set()
    duplicates = set()
    for item in arr:
        if item in seen:
            duplicates.add(item)
        else:
            seen.add(item)
    return list(duplicates)

Complexity: O(n) time, O(n) space

Verdict

MAJOR_CONCERNS - O(n²) algorithm unsuitable for production data sizes. Optimized version recommended.

## References

- **Profiling Tools:** `scripts/performance-profile.ps1`, py-spy, clinic.js
- **Monitoring:** `docs/guides/observability.md`
- **Cost Analysis:** AWS Cost Explorer, GCP Pricing Calculator
- `.github/agents/performance.agent.md` — performance-focused review persona and workflow
- `instructions/workflows/reviewer.instructions.md` — review guardrails when performance becomes a quality gate