Write-through pattern in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis write-through cache sequence?

Consider a Redis cache used with a write-through pattern. The application writes a key user:1 with value "Alice" to Redis and the database simultaneously. Then it reads the key user:1 from Redis.

What will the Redis GET command return?

Redis

SET user:1 "Alice"
GET user:1

A nil

B "Alice"

C SyntaxError

D "user:1"

💡 Hint

In write-through caching, data is written to cache and database at the same time.

Since the write-through pattern writes data to Redis immediately, the GET command returns the stored value "Alice".

🧠 Conceptual

intermediate

Why is write-through caching beneficial for data consistency?

Which of the following best explains why write-through caching helps keep data consistent between cache and database?

A Because data is written to cache and database simultaneously

B Because cache is updated only when data is read from database

C Because data is written to cache only after database write succeeds

D Because cache is cleared after every write to database

💡 Hint

Think about when the cache and database get updated in write-through.

Write-through caching writes data to both cache and database at the same time, ensuring they stay consistent.

📝 Syntax

advanced

Which Redis command sequence correctly implements a write-through cache update?

You want to update the user name for user:2 in Redis cache and the database using write-through. Which Redis command sequence below correctly updates the cache?

A

DEL user:2
SET user:2 "Bob"

B SETNX user:2 "Bob"

C SET user:2 "Bob"

D

GET user:2
SET user:2 "Bob"

💡 Hint

Write-through means writing the new value directly to cache.

Using SET directly updates the cache with the new value, which is required for write-through.

❓ optimization

advanced

How can write-through caching impact write latency and how to mitigate it?

Write-through caching writes data to both cache and database synchronously. What is a common impact on write latency and a typical way to reduce it?

A Increases latency; mitigate by batching writes asynchronously

B Decreases latency; mitigate by adding more cache servers

C No impact on latency; mitigate by using faster database

D Increases latency; mitigate by disabling cache writes

💡 Hint

Think about writing to two places at once and how to improve speed.

Write-through increases write latency because it waits for both cache and database writes. Batching writes asynchronously can reduce this latency.

🔧 Debug

expert

What error occurs if Redis SET command is used incorrectly in write-through caching?

Given this Redis command used in a write-through cache update:

SET user:3

What error will Redis return?

A "OK"

B (error) ERR syntax error

C nil

D (error) ERR wrong number of arguments for 'set' command

💡 Hint

Check the required arguments for the SET command.

The SET command requires a key and a value. Missing the value causes a wrong number of arguments error.