Caching: ElastiCache for Redis vs Memcached, DynamoDB Accelerator (DAX), lazy loading vs write-through

A cache keeps frequently read data in fast memory so that repeated requests do not hit a slower database. That lowers latency, often from milliseconds to microseconds, and reduces load and cost on the database, because fewer reads reach it and it can often be a smaller size. Caching works best for data that is read far more often than it changes, such as product catalogs, user profiles and session data. The exam asks two kinds of question: which cache service fits, and which caching strategy fits.