Cache warming strategies in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a key-value pair in Redis cache.

Redis

SET "user:1001" "John Doe" [1]

Drag options to blanks, or click blank then click option'

AXX

BNX

CPX

DEX

Attempts:

3 left

💡 Hint

Common Mistakes

Using EX or PX which set expiration but do not control existence.

Using XX which sets only if key exists, not for warming.

The NX option sets the key only if it does not already exist, which is useful for cache warming to avoid overwriting existing cache.

2fill in blank

medium

Complete the code to preload multiple keys into Redis cache using a pipeline.

Redis

redis.pipeline()[1]

Drag options to blanks, or click blank then click option'

A.execute()

B.flushall()

C.get('user:1')

D.set('user:1', 'Alice')

Attempts:

3 left

💡 Hint

Common Mistakes

Calling execute immediately without adding commands.

Using flushall which clears the cache.

Using pipeline().set() allows batching multiple set commands to warm the cache efficiently.

3fill in blank

hard

Fix the error in the Lua script that preloads cache keys only if they don't exist.

Redis

if redis.call('EXISTS', [1]) == 0 then redis.call('SET', [1], ARGV[1]) end

Drag options to blanks, or click blank then click option'

AKEYS[2]

BARGV[1]

CKEYS[1]

DARGV[2]

Attempts:

3 left

💡 Hint

Common Mistakes

Using ARGV for keys causes errors.

Using wrong index in KEYS or ARGV arrays.

In Redis Lua scripts, keys are passed via KEYS array. To check existence of the first key, use KEYS[1].

4fill in blank

hard

Fill both blanks to create a Redis command that preloads keys with expiration only if they don't exist.

Redis

SET [1] [2] NX EX 3600

Drag options to blanks, or click blank then click option'

Auser:2001

BJohn

Cuser:3001

DAlice

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping key and value positions.

Using keys that do not match the value.

The command sets key user:2001 with value John only if the key does not exist, with expiration of 3600 seconds.

5fill in blank

hard

Fill all three blanks to write a Lua script that warms cache by setting multiple keys with values only if they don't exist.

Redis

for i, key in ipairs([1]) do if redis.call('EXISTS', key) == 0 then redis.call('SET', key, [2][i]) end end return [3]

Drag options to blanks, or click blank then click option'

A{'user:1', 'user:2', 'user:3'}

B{'Alice', 'Bob', 'Carol'}

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using mismatched keys and values.

Returning false instead of true.

Not using tables for keys and values.

The script loops over keys {'user:1', 'user:2', 'user:3'} and sets their values from {'Alice', 'Bob', 'Carol'} only if keys don't exist, then returns true.

Practice

1. What is the main purpose of cache warming in Redis?

easy

A. To clear all data from the cache

B. To backup Redis data to disk

C. To preload data into cache before it is requested

D. To monitor cache hit rates

Solution

1. Step 1: Understand cache warming concept

   Cache warming means loading data into cache before users request it to speed up access.

2. Step 2: Identify the correct purpose

   Preloading data matches the definition of cache warming, unlike clearing, backing up, or monitoring.

3. Final Answer:

   To preload data into cache before it is requested -> Option C

4. Quick Check:

   Cache warming = preload data [OK]

Hint: Cache warming means loading data early [OK]

Common Mistakes:

• Confusing cache warming with cache clearing
• Thinking cache warming is about backups
• Mixing cache warming with monitoring tasks

2. Which Redis command is used to preload multiple key-value pairs for cache warming?

easy

A. GET

B. MSET

C. DEL

D. EXPIRE

Solution

1. Step 1: Recall Redis commands for setting data

   SET sets one key-value pair; MSET sets multiple pairs at once.

2. Step 2: Identify command for multiple keys

   MSET is designed to preload many keys efficiently, perfect for cache warming.

3. Final Answer:

   MSET -> Option B

4. Quick Check:

   MSET = preload multiple keys [OK]

Hint: Use MSET to set many keys at once [OK]

Common Mistakes:

• Using GET instead of SET to preload data
• Confusing DEL (delete) with setting commands
• Using EXPIRE which only sets timeouts

3. Given the Redis commands:

MSET user:1 "Alice" user:2 "Bob" user:3 "Carol"

What will GET user:2 return immediately after?

medium

A. "Alice"

B. Error

C. nil

D. "Bob"

Solution

1. Step 1: Understand MSET effect

   MSET sets multiple keys: user:1 to "Alice", user:2 to "Bob", user:3 to "Carol".

2. Step 2: Check GET user:2 result

   GET user:2 returns the value set by MSET, which is "Bob".

3. Final Answer:

   "Bob" -> Option D

4. Quick Check:

   GET user:2 = "Bob" [OK]

Hint: MSET sets all keys, GET returns the exact value [OK]

Common Mistakes:

• Assuming GET returns first key's value
• Expecting nil if not refreshed
• Confusing key names or values

4. You try to warm cache with:

MSET user:1 "Alice" user:2

What is the problem with this command?

medium

A. MSET requires an even number of arguments

B. MSET cannot set string values

C. MSET only accepts one key-value pair

D. MSET keys must start with 'cache:' prefix

Solution

1. Step 1: Check MSET argument rules

   MSET expects pairs of key and value, so arguments count must be even.

2. Step 2: Analyze given command

   The command ends with key 'user:2' but no value, so arguments are odd.

3. Final Answer:

   MSET requires an even number of arguments -> Option A

4. Quick Check:

   MSET args count even = true [OK]

Hint: MSET needs pairs: key and value [OK]

Common Mistakes:

• Thinking MSET accepts single key without value
• Believing keys must have special prefixes
• Assuming MSET can set non-string values only

5. You want to warm cache with user data but only for users with active status. Given:

users = {"1": "Alice", "2": "Bob", "3": "Carol"}
active_users = ["1", "3"]

Which Redis command sequence correctly warms cache only for active users?

hard

A. MSET user:1 "Alice" user:3 "Carol"

B. MSET user:1 "Alice" user:2 "Bob" user:3 "Carol"

C. SET user:2 "Bob"

D. DEL user:2

Solution

1. Step 1: Identify active users to cache

   Only users "1" and "3" are active, so only their data should be cached.

2. Step 2: Choose command that sets only active users

   MSET with keys user:1 and user:3 sets only active users, matching requirement.

3. Final Answer:

   MSET user:1 "Alice" user:3 "Carol" -> Option A

4. Quick Check:

   Cache only active users = MSET user:1 and user:3 [OK]

Hint: Warm cache only for active users with MSET [OK]

Common Mistakes:

• Caching all users ignoring active status
• Using DEL or SET for inactive users incorrectly
• Confusing which users to preload