Lesson 3: Caching#

Why Cache?#

Caching is the process of storing copies of data in a temporary storage location (cache) so that future requests for that data can be served faster.

• Reduce Latency: Memory is faster than disk.
• Reduce Load: Fewer queries to the database.

Caching Strategies#

Cache-Aside (Lazy Loading)#

1. App checks cache.
2. If miss, App reads from DB.
3. App writes to cache.

• Pros: Only requested data is cached.
• Cons: Initial request is slow (cache miss).

Write-Through#

1. App writes to cache and DB simultaneously.

• Pros: Data in cache is always fresh.
• Cons: Slower writes.

Write-Back (Write-Behind)#

1. App writes to cache only.
2. Cache writes to DB asynchronously.

• Pros: Fast writes.
• Cons: Data loss risk if cache fails before syncing.

Eviction Policies#

When the cache is full, what do you remove?

• LRU (Least Recently Used): Remove the item that hasn’t been used for the longest time.
• LFU (Least Frequently Used): Remove the item used least often.
• FIFO (First In, First Out): Remove the oldest item.

🛠️ Sruja Perspective: Modeling Caches#

In Sruja, caches are often modeled as separate containers or components.

architecture "Product Catalog" {
    system Catalog "Product Catalog System" {
        container WebApp "Storefront" {
            technology "Node.js"
        }

        container ProductCache "Product Cache" {
            technology "Memcached"
            description "Caches product details using LRU eviction."
        }

        container ProductDB "Product Database" {
            technology "MongoDB"
        }

        WebApp -> ProductCache "Read (Cache-Aside)"
        WebApp -> ProductDB "Read on Miss"
    }
}