Denormalization for speed in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis command sequence?

Given these Redis commands executed in order:

1. HSET user:1000 name "Alice" age 30
2. HSET user:1000:profile city "New York" country "USA"
3. HMGET user:1000 name age
4. HMGET user:1000:profile city country

What will be the combined output of commands 3 and 4?

Redis

HSET user:1000 name "Alice" age 30
HSET user:1000:profile city "New York" country "USA"
HMGET user:1000 name age
HMGET user:1000:profile city country

A ["Alice", null] and ["New York", "USA"]

B ["name", "age"] and ["city", "country"]

C ["Alice", "30"] and ["New York", "USA"]

D [null, null] and [null, null]

💡 Hint

Remember that HMGET returns the values of the specified fields in the hash.

The first HMGET fetches the 'name' and 'age' fields from 'user:1000' hash, which were set to 'Alice' and 30 respectively. The second HMGET fetches 'city' and 'country' from 'user:1000:profile' hash, set to 'New York' and 'USA'.

🧠 Conceptual

intermediate

Why is denormalization used in Redis for speed?

Which of the following best explains why denormalization is commonly used in Redis to improve speed?

A Denormalization reduces the number of queries by storing related data together, avoiding expensive joins.

B Denormalization compresses data to use less memory, making queries faster.

C Denormalization encrypts data to improve security and speed.

D Denormalization automatically indexes all fields for faster search.

💡 Hint

Think about how Redis handles data and what it lacks compared to relational databases.

Redis does not support joins like relational databases. Denormalization stores related data together to reduce the number of queries and speed up data retrieval.

📝 Syntax

advanced

Which Redis command syntax correctly denormalizes user and order data?

You want to store user data and their latest order details together in Redis for fast access. Which command correctly sets a hash with user info and embedded order info?

A HSET user:2000 name "Bob" age 25 order_id 1234 order_total 99.99

B HSET user:2000 name "Bob" age 25; HSET order:1234 total 99.99

C HMSET user:2000 name "Bob" age 25; SET order:1234 99.99

D HSET user:2000 name "Bob" age 25 order {id:1234, total:99.99}

💡 Hint

Redis hashes store flat field-value pairs; nested objects require flattening.

Option A correctly uses HSET with flat field-value pairs including order info as separate fields. Option A tries to store a nested object which Redis does not support natively in hashes.

❓ optimization

advanced

How to optimize read speed with denormalized data in Redis?

You have user profiles and their recent activity logs stored separately. To optimize read speed for a dashboard showing both, what is the best denormalization strategy?

A Use Redis streams to store activity logs and join with profiles at query time.

B Keep user profiles and activity logs in separate keys and query both on demand.

C Store only user profiles in Redis and fetch activity logs from a relational database.

D Store user profile and recent activity fields together in one hash per user.

💡 Hint

Denormalization means combining related data to reduce queries.

Combining user profile and recent activity in one hash reduces the number of Redis calls, improving read speed for dashboards.

🔧 Debug

expert

Why does this denormalized Redis data retrieval fail?

You stored denormalized user data with order info as:

HSET user:3000 name "Carol" age 40 order_id 5678 order_total 150.00

But this command returns null:

HMGET user:3000 order

Why?

A Because Redis hashes cannot store multiple fields with underscores.

B Because 'order' is not a field; fields are 'order_id' and 'order_total', so HMGET 'order' returns null.

C Because HMGET requires all fields to be numeric.

D Because the key 'user:3000' does not exist.

💡 Hint

Check the exact field names stored in the hash.

The hash has fields 'order_id' and 'order_total', but no field named 'order'. HMGET 'order' returns null because that field does not exist.