Cache stampede prevention in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a cache key with an expiration time to prevent stale data.

Redis

redis.set('user:123', user_data, ex=[1])

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

A-1

BNone

C3600

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or negative values disables expiration, causing stale cache.

Setting an expiration time (in seconds) like 3600 ensures the cache expires after one hour, helping prevent stale data.

2fill in blank

medium

Complete the code to acquire a lock key before regenerating cache to prevent cache stampede.

Redis

if redis.setnx('lock:user:123', '1'):
    redis.expire('lock:user:123', [1])
    # regenerate cache

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

A10

B-5

CNone

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Not setting expiration can cause deadlocks.

Setting a short expiration (like 10 seconds) on the lock prevents deadlocks if the process crashes.

3fill in blank

hard

Fix the error in the code that tries to get cached data and falls back to regeneration if missing.

Redis

data = redis.get('user:123')
if data is [1]:
    # regenerate cache

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

AFalse

B''

C0

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for False or empty string causes incorrect cache miss detection.

Redis returns None if the key does not exist, so checking for None detects cache miss.

4fill in blank

hard

Fill both blanks to implement a safe cache regeneration with lock and expiration.

Redis

if redis.setnx('lock:user:123', '1'):
    redis.expire('lock:user:123', [1])
    data = regenerate_data()
    redis.set('user:123', data, ex=[2])
    redis.delete('lock:user:123')

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

A10

B3600

C60

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Setting lock expiration too long causes blocking.

Setting cache expiration too short causes frequent regeneration.

Lock expiration is short (10 seconds) to avoid deadlocks. Cache expiration is longer (3600 seconds) to keep data fresh.

5fill in blank

hard

Fill all three blanks to implement cache stampede prevention with lock check, regeneration, and fallback.

Redis

data = redis.get('user:123')
if data is [1]:
    if redis.setnx('lock:user:123', '1'):
        redis.expire('lock:user:123', [2])
        data = regenerate_data()
        redis.set('user:123', data, ex=[3])
        redis.delete('lock:user:123')
    else:
        time.sleep(0.1)
        data = redis.get('user:123')

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

ANone

B10

C3600

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using False instead of None for cache miss.

Not setting lock expiration.

Setting cache expiration too short.

Check for None to detect cache miss. Lock expiration is short (10 seconds). Cache expiration is longer (3600 seconds) to keep data fresh.