Caching Strategies

Definition

The process of storing copies of frequently accessed data in a temporary, high-speed storage layer so that future requests for that data are served much faster.

Explain Like I'm New

Imagine asking a librarian 'Who won the 1994 World Cup?'. She walks to the basement, searches 10 books, and 15 minutes later says 'Brazil' (A slow Database Query). Five minutes later, someone else asks her the exact same question. Does she go back to the basement? No! She memorized the answer (Caching). She answers 'Brazil' instantly.

Real World Example

A news website. The 'Top 10 Articles' query takes 2 seconds to run against the database. Since the top 10 articles only change once an hour, you cache the result. For the next hour, all 50,000 users get the articles instantly in 5 milliseconds without the database doing any work.

Common Use Cases

•Drastically improving API response times
•Reducing database server costs
•Surviving traffic spikes

Interactive Example

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Interview Questions

basic

What is a Cache 'Hit' vs a Cache 'Miss'?

intermediate

What is 'Cache Invalidation'?

Flash Cards

Question

Hit vs Miss?

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Answer

A Hit means the data was found in the cache, and returned instantly. A Miss means the data wasn't there (or expired), so the server is forced to run the slow database query.

Question

What is Cache Invalidation?

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Answer

The hardest problem in computer science. It is the process of deleting or updating cached data when the source database changes. If you don't invalidate the cache, users will see stale, outdated data.