Exam AWS Certified Database - Specialty topic 1 question 280 discussion

B is answer. Write through means low availability while providing fresh data, so A and D are out. Memcached is incorrect in terms of HA, because it doesn't have replication feature and would lose data when node failure occur. There's an exception, though. If Memcached is severless, C would be answer. It supports replication https://aws.amazon.com/blogs/aws/amazon-elasticache-serverless-for-redis-and-memcached-now-generally-available/

C. Noted that: 1. The news website needs HA, not the cache system. 2. Write-though can't rescue node failure or scaling out, whereas lazy-loading stale data can be overcome by adding TTL. 3. Simpler, easy to scale out goes to Memcached; complex and fancy features goes to Redis. So A and D dropped because no write-though. Pick C and drop B due to simpler, scale-out architecture. https://docs.aws.amazon.com/AmazonElastiCache/latest/mem-ug/SelectEngine.html https://docs.aws.amazon.com/AmazonElastiCache/latest/mem-ug/Strategies.html

It does not matter if you lose a Memcached node - any data lost will be reloaded from the source. You do not need replication of data offered by Redis. "Short TTL" is a relative term. A new story is newsworthy 24 hrs? Is that short enough to qualify as short? How long is a long TTL?

This is not an easy one... One has to choose between * Redis or Memcached * write-through and long TTL, or short TTL with lazy loading I'll choose lazy loading because there is no way of saying whether an article will be popular I'll choose Memcached because there is no need for complex data structures and Memcached scales better vertically.

A long time to live (TTL) is recommended in this scenario because news pages are unlikely to change frequently. Setting a long TTL will allow the cached data to be reused for a longer period, reducing the number of requests to the database and improving page load times. Therefore, the correct answer is D. Use ElastiCache for Redis with write-through and long time to live (TTL).

D. Use ElastiCache for Redis with write-through and long time to live (TTL). The use case requires improving the page load time of a highly available news website, especially during popular news releases, where there is a high level of traffic. ElastiCache can help in achieving this by caching frequently accessed data in-memory, reducing the number of requests to the database and improving the overall performance of the website. Redis is recommended for this use case because it provides better performance for read-intensive workloads and has more advanced features for caching, such as write-through caching. Write-through caching ensures that any changes made to the data in the cache are also written back to the database, ensuring data consistency.

long time to live as the articles are unlikely to change. Redis over Memcached, as it supports a wider range of data structures.

Why not Memcache though? Can someone please explain?

D is the answer - Since the news is not likely to change it will be there once it is written and with long TTL it will be there for longer time.

D right answer

Elasticache for redis since application needs to be highly available. Memcache dont have HA. Lazy Writing since there is no much modifications expected on page.