Cache invalidation strategies in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the cache expiration time to 60 seconds.

Rest API

cache.set('user_data', data, timeout=[1])

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

A600

B60

C6

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting timeout to 0 disables caching.

Using too large timeout causes stale data.

The timeout parameter defines how long the cache stores data. Setting it to 60 means the cache expires after 60 seconds.

2fill in blank

medium

Complete the code to invalidate the cache for the key 'user_data'.

Rest API

cache.[1]('user_data')

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

Aupdate

Brefresh

Cdelete

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set instead of delete.

Using update which modifies but does not remove.

To remove cached data, you use the delete method with the cache key.

3fill in blank

hard

Fix the error in the code to invalidate cache after updating user info.

Rest API

def update_user(user_id, new_info):
    save_to_db(user_id, new_info)
    cache.[1](f'user_{user_id}')

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

Adelete

Bget

Cset

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using set which overwrites cache without new data.

Using get which only reads cache.

After updating the database, you must delete the cache entry to avoid stale data.

4fill in blank

hard

Fill both blanks to create a cache key with user ID and set cache with 120 seconds timeout.

Rest API

cache_key = f'user_[1]'
cache.set(cache_key, user_data, timeout=[2])

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

Aid

B120

Cuser_id

D60

Attempts:

3 left

💡 Hint

Common Mistakes

Using id instead of user_id which may not be defined.

Setting timeout to 60 instead of 120.

The cache key uses the variable user_id to identify the user. The timeout is set to 120 seconds for cache expiration.

5fill in blank

hard

Fill all three blanks to implement cache invalidation after updating user profile and then set new cache.

Rest API

def update_profile(user_id, profile):
    db.update(user_id, profile)
    cache.[1](f'user_[2]')
    cache.set(f'user_[3]', profile, timeout=300)

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

Adelete

Buser_id

Cid

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set instead of delete to remove old cache.

Mixing id and user_id causing key mismatch.

After updating the database, delete the old cache using the user_id key, then set new cache with the updated profile and a 300 seconds timeout.

Practice

1. Which cache invalidation strategy automatically removes cached data after a set period of time?

easy

A. Manual invalidation

B. Event-based invalidation

C. Time-based invalidation

D. Versioning invalidation

Solution

1. Step 1: Understand time-based invalidation

   Time-based invalidation removes cached data after a fixed time, ensuring data freshness automatically.

2. Step 2: Compare with other strategies

   Manual invalidation requires user action, event-based depends on data changes, and versioning uses data versions.

3. Final Answer:

   Time-based invalidation -> Option C

4. Quick Check:

   Automatic removal after time = Time-based invalidation [OK]

Hint: Time-based means cache expires after set time [OK]

Common Mistakes:

• Confusing manual with automatic removal
• Thinking event-based triggers on time
• Mixing versioning with time expiry

2. Which of the following is the correct way to manually invalidate a cache entry in a REST API?

easy

A. Send a PUT request to update cached data

B. Send a GET request to the cache endpoint

C. Send a POST request to retrieve cached data

D. Send a DELETE request to the cache endpoint

Solution

1. Step 1: Identify HTTP method for deletion

   DELETE requests are used to remove resources, including cache entries.

2. Step 2: Understand other methods

   GET retrieves data, POST creates, and PUT updates; none remove cache.

3. Final Answer:

   Send a DELETE request to the cache endpoint -> Option D

4. Quick Check:

   DELETE removes cache entry manually [OK]

Hint: DELETE method removes resources like cache entries [OK]

Common Mistakes:

• Using GET to remove cache
• Confusing POST with deletion
• Thinking PUT deletes cache

3. Consider this pseudo-code for event-based cache invalidation:

if (dataChangedEvent) {
  invalidateCache(key);
}
return getCachedData(key);

What will happen if dataChangedEvent is true?

medium

A. Cache is invalidated and fresh data is fetched next time

B. Cache remains unchanged and stale data is returned

C. Cache is updated without invalidation

D. An error occurs because cache cannot be invalidated

Solution

1. Step 1: Analyze the condition

   If dataChangedEvent is true, invalidateCache(key) runs, removing cached data.

2. Step 2: Understand cache behavior after invalidation

   After invalidation, next data fetch will get fresh data, not stale cache.

3. Final Answer:

   Cache is invalidated and fresh data is fetched next time -> Option A

4. Quick Check:

   Event triggers invalidation = fresh data next fetch [OK]

Hint: Event true means cache cleared for fresh data [OK]

Common Mistakes:

• Assuming cache stays after invalidation
• Thinking cache updates automatically
• Believing invalidation causes errors

4. You have this code snippet for versioning cache invalidation:

cache = { 'v1': data1 }
function getData(version) {
  return cache[version];
}

// Later
cache['v2'] = newData;

What is the main bug if the client still requests v1 after update?

medium

A. Cache throws an error because version key is missing

B. Client gets stale data because old version is still cached

C. Cache automatically updates old version to new data

D. Client cannot access any cached data

Solution

1. Step 1: Understand versioning cache behavior

   Old version 'v1' remains in cache, so requests for it get stale data.

2. Step 2: Identify bug impact

   Client requesting 'v1' does not see 'v2' data, causing stale responses.

3. Final Answer:

   Client gets stale data because old version is still cached -> Option B

4. Quick Check:

   Old version key returns stale data [OK]

Hint: Old version keys keep stale data unless removed [OK]

Common Mistakes:

• Assuming cache auto-updates old versions
• Expecting errors on missing keys
• Thinking client loses all cache access

5. You want to design a cache invalidation strategy for a REST API where data changes frequently but must stay fresh within 5 minutes. Which combined strategy is best?

hard

A. Use time-based invalidation with 5-minute expiry plus event-based invalidation on data changes

B. Use manual invalidation only, requiring user to clear cache

C. Use versioning only without time limits

D. Use time-based invalidation with 1-hour expiry only

Solution

1. Step 1: Analyze freshness requirement

   Data must be fresh within 5 minutes, so time-based expiry should be 5 minutes or less.

2. Step 2: Combine with event-based invalidation

   Event-based invalidation clears cache immediately on data changes, improving freshness.

3. Step 3: Evaluate other options

   Manual invalidation is slow, versioning alone may keep stale data, and 1-hour expiry is too long.

4. Final Answer:

   Use time-based invalidation with 5-minute expiry plus event-based invalidation on data changes -> Option A

5. Quick Check:

   Combine time and event for fresh cache [OK]

Hint: Combine time and event for best freshness [OK]

Common Mistakes:

• Relying only on manual invalidation
• Using too long expiry times
• Ignoring event triggers for changes