Refresh Ahead

🔁 Refresh-Ahead Caching — Explained

Refresh-Ahead is a caching strategy where the cache is proactively updated before it expires, instead of waiting for a user to request the data after expiration.

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🧠 Why Refresh-Ahead?

In normal TTL-based caching, when data expires:

• The first user after expiry suffers a slow response (cache miss).

• Everyone after that benefits.

With refresh-ahead, the system preloads the new data into the cache in advance, so no one hits a cold cache.

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🔄 How It Works

[Time-Based TTL] → Suppose TTL = 10 minutes

[Refresh Threshold] = 9 minutes

When time > 9 min, the system fetches new data in the background
→ Replaces cache BEFORE expiry
→ User never sees stale or missing data

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📊 Real-World Use Cases

• Product catalog pages on e-commerce platforms

• Dashboard stats in admin panels

• Weather or stock ticker services

• ML model inference caching for repeated inputs

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🛠️ Example with Redis (Pseudocode)

// Pseudo refresh-ahead logic
if (cache.isCloseToExpire(key)) {
  refreshInBackground(key);
}
return cache.get(key);

Some libraries or tools (like Caffeine in Java, or Redis with Lua scripts) support refresh-ahead behavior out of the box.

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✅ Advantages

• Consistently low latency (no cold cache)

• Better user experience

• Prevents cache stampede (many users hitting backend at once on expiry)

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❌ Disadvantages

• More backend load (you refresh even if no user asks)

• Higher resource usage for rarely used data

• More complexity to manage background refresh safely

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🚦 When to Use Refresh-Ahead

Use it when:

• You have high traffic or predictable access patterns

• Data needs to be always warm

• Backend supports background refresh efficiently