• Amazon ElastiCache
  • Caching Strategies
    • Lazy loading
    • Write through
  • Redis vs MemCached
    • Redis
    • Memcached

Amazon ElastiCache

Caching Strategies

A cache hit occurs when the cache contains the information requested.
A cache miss occurs when the cache does not contain the information requested.

Lazy loading

It’s a caching strategy that loads data into the cache only when necessary.
When your application requests data, it first makes the request to the cache. If the data exists in the cache (a cache hit), it is retrieved; but if it does not or has expired (a cache miss), then the data is retrieved from your data store and then stored in the cache.

• Advantage: only the requested data is cached
• Disadvantage: is that there is a cache miss penalty.

Write through

It’s a strategy that adds/updetes data or in the cache whenever data is written to the database.

• Advantage: data in the cache is never stale.
• Disadvantages:
  • write penalty because every write involves two trips (cache and database)
  • cost because there can be data that is stored but never used
  • if data is updated frequently will cause cache churn

Redis vs MemCached

Redis

Redis is an increasingly popular open-source, key-value store that supports more advanced data structures, such as sorted sets, hashes, and lists. Unlike Memcached, Redis has disk persistence built in, meaning that you can use it for long-lived data. Redis also supports replication, which can be used to achieve Multi-AZ redundancy.

Memcached

It’s a widely adopted in-memory key store. It is historically the gold standard of web caching. ElastiCache is protocol-compliant with Memcached, and it is designed to work with popular tools that you use today with existing Memcached environments. Memcached is also multithreaded, meaning that it makes good use of larger Amazon EC2 instance sizes with multiple cores.

Feature	MemCached	Redis
Horizontal scalability	X
Multi thread	X
Advanced data types		X
Sort/rank data sets		X
Pub/Sub capabilities		X
MultiAZ with auto failover		X
Backup and restore		X