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mediumSystem Design

How does caching improve system performance?

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01

Understand the problem

Explain caching and strategies.

caching
02

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How Does Caching Improve System Performance?

Target Audience: Junior & Senior Software Engineers preparing for System Design Interviews — no prior system design knowledge assumed. Difficulty: Easy to Medium

How to read this doc: Every concept is explained in plain language first. Right after, you'll s

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04

Read the code

LRU cache with eviction
Run Playground
class LRUCache {
  constructor(capacity) {
    this.capacity = capacity;
    this.cache = new Map(); // key -> value
    this.order = [];        // most-recently-used at the end
  }

  get(key) {
    if (!this.cache.has(key)) return -1;
    this.order.splice(this.order.indexOf(key), 1);
    this.order.push(key);
    return this.cache.get(key);
  }

  put(key, value) {
    if (this.cache.has(key)) {
      this.order.splice(this.order.indexOf(key), 1);
    } else if (this.cache.size >= this.capacity) {
      const lruKey = this.order.shift();
      this.cache.delete(lruKey);
    }
    this.cache.set(key, value);
    this.order.push(key);
  }
}

const cache = new LRUCache(2);
cache.put('a', 1);
cache.put('b', 2);
console.log('get(a):', cache.get('a'));
cache.put('c', 3);
console.log('get(b):', cache.get('b'));
console.log('get(a):', cache.get('a'));
console.log('get(c):', cache.get('c'));
Cache-aside read
Run Playground
cache = {}                      # stand-in for Redis/Memcached

def load_from_db(key):
    print("  DB read for", key)
    return key.upper() + "-value"

def get(key):
    if key in cache:            # 1. check cache
        return cache[key]       # 2a. hit
    value = load_from_db(key)   # 2b. miss -> load
    cache[key] = value          # 3. populate
    return value

print(get("user:1"))            # miss -> DB
print(get("user:1"))            # hit  -> no DB read
print(get("user:2"))            # miss -> DB
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