Identify Bottlenecks: Profile application, analyze metrics
Choose Strategy: Select caching, scaling, or optimization approach
Implement Cache: Set up Redis/Memcached with appropriate pattern
Configure Scaling: Horizontal or vertical based on needs
Monitor Results: Set up APM and track improvements

Caching Patterns

Pattern	Use Case	Consistency	Complexity
Cache-Aside	Read-heavy, tolerates stale	Eventual	Low
Write-Through	Write-heavy, needs consistency	Strong	Medium
Write-Behind	High throughput writes	Eventual	High
Refresh-Ahead	Predictable access	Strong	Medium

Decision Tree

Performance Issue?
    │
    ├─→ High latency → Check database queries
    │     ├─→ Slow queries → Add indexes, optimize SQL
    │     └─→ Network → Add caching, reduce round-trips
    │
    ├─→ High CPU → Profile code
    │     ├─→ Algorithmic → Optimize algorithms
    │     └─→ Too much load → Scale horizontally
    │
    └─→ Memory issues → Analyze memory usage
          ├─→ Leaks → Find and fix leaks
          └─→ Large data → Implement pagination, streaming

Examples

Example 1: Redis Cache-Aside

import redis
import json
from functools import wraps

r = redis.Redis(host='localhost', port=6379, decode_responses=True)

def cache(ttl_seconds=3600):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            cache_key = f"{func.__name__}:{args}:{kwargs}"
            cached = r.get(cache_key)
            if cached:
                return json.loads(cached)

            result = func(*args, **kwargs)
            r.setex(cache_key, ttl_seconds, json.dumps(result))
            return result
        return wrapper
    return decorator

@cache(ttl_seconds=300)
def get_expensive_data(user_id: str) -> dict:
    # Expensive database query or computation
    return {"user_id": user_id, "data": "..."}

Example 2: Connection Pooling

from sqlalchemy import create_engine

engine = create_engine(
    DATABASE_URL,
    pool_size=20,
    max_overflow=10,
    pool_timeout=30,
    pool_recycle=1800,
    pool_pre_ping=True
)

Example 3: Load Balancing (nginx)

upstream backend {
    least_conn;  # Least connections algorithm
    server backend1:8000 weight=3;
    server backend2:8000 weight=2;
    server backend3:8000 weight=1;

    keepalive 32;  # Connection pooling
}

server {
    location /api {
        proxy_pass http://backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
    }
}

Performance Metrics

Latency Targets:
├── P50: < 50ms   (typical request)
├── P95: < 200ms  (most requests)
├── P99: < 500ms  (almost all)
└── P99.9: < 1s   (worst case)

Cache Metrics:
├── Hit Ratio: > 90% (ideal)
├── Eviction Rate: Low (stable)
└── Memory Usage: < 80% (headroom)

Database Metrics:
├── Connection Pool: < 80% utilized
├── Query Time: P95 < 100ms
└── Slow Queries: < 1% of total

Troubleshooting

Common Issues

Issue	Cause	Solution
High cache miss	Poor key design	Review key patterns
Cache stampede	Many misses at once	Use locks or jitter
Memory pressure	Over-caching	Set TTL, eviction policy
Connection timeout	Pool exhausted	Increase pool size

Debug Commands

# Redis stats
redis-cli INFO stats | grep -E 'keyspace|hits|misses'

# Memory usage
redis-cli INFO memory | grep used_memory_human

# Slow queries
redis-cli SLOWLOG GET 10

# Load test
wrk -t12 -c400 -d30s http://localhost/api

Test Template

# tests/test_performance.py
import pytest
import time

class TestCachePerformance:
    def test_cache_hit_is_fast(self, redis_client):
        # First call - cache miss
        start = time.time()
        result1 = get_cached_data("key1")
        cold_time = time.time() - start

        # Second call - cache hit
        start = time.time()
        result2 = get_cached_data("key1")
        warm_time = time.time() - start

        assert warm_time < cold_time * 0.1  # 10x faster
        assert result1 == result2

    def test_cache_ttl_expires(self, redis_client):
        set_cached_data("key", "value", ttl=1)
        time.sleep(2)
        assert get_cached_data("key") is None

Caching Patterns

Decision Tree

Examples

Example 1: Redis Cache-Aside

Example 2: Connection Pooling

Example 3: Load Balancing (nginx)

Performance Metrics

Troubleshooting

Common Issues

Debug Commands

Test Template

Resources

performance

Performance Optimization Skill

Quick Start

Instructions