Scaling Reads medium
A popular cache key expires. 5000 requests hit the server at once. They all miss the cache and hit the database. What fixes this?
- A Request Coalescing (Singleflight): Group the 5000 requests, send 1 query to DB, and share the result.
- B Disable the cache.
- C Restart the database.
- D Use a shorter TTL.
Answer: A. Request Coalescing (Singleflight): Group the 5000 requests, send 1 query to DB, and share the result.
Coalescing ensures that only one 'worker' does the hard work of regeneration, while the others wait for that worker to return.
One system design question a day, with spaced repetition so the ones you miss come back.
Get the appRelated questions
- In a caching system, what is a 'Cache Miss'?
- Why is `SELECT * FROM Users` generally discouraged in high-performance applications compared to `SELECT name, email FROM Users`?
- You have users all over the world downloading large images from your server in New York. Users in Australia complain it is slow. What solves this?
- What is the main downside of reading from a Read Replica instead of the Primary database?
- You have maximized the RAM on your single database server, but it's still too slow. You decide to add 10 more servers to share the load. What is this called?
- You have 5 Read Replicas. How does the application know which one to ask for data?