Cache stampede prevention in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the cache key for storing user data.

HLD

cache_key = "user_data_[1]"

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

Arequest_id

Buser_id

Ctimestamp

Dsession_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using session_id or request_id which are not stable identifiers for user data.

The cache key should uniquely identify the user data, so using user_id is correct.

2fill in blank

medium

Complete the code to check if the cache has expired before fetching fresh data.

HLD

if cache_timestamp [1] current_time:

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

A<

B>

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or == which do not correctly detect expiration.

We check if the cache timestamp is less than the current time to know if it expired.

3fill in blank

hard

Fix the error in the code to acquire a lock before refreshing the cache.

HLD

if cache_miss:
    if cache_lock.[1]():
        refresh_cache()

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

Await

Bunlock

Cacquire

Drelease

Attempts:

3 left

💡 Hint

Common Mistakes

Using release or unlock before acquiring the lock.

To prevent multiple processes from refreshing the cache simultaneously, we must acquire a lock first.

4fill in blank

hard

Fill both blanks to implement cache stampede prevention using a lock and cache update.

HLD

if cache_expired:
    if cache_lock.[1]():
        data = fetch_fresh_data()
        cache_store.[2](cache_key, data)

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

Aacquire

Bdelete

Cset

Drelease

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete instead of set to update cache.

First, we acquire the lock to prevent others from refreshing simultaneously. Then, we set the fresh data in the cache.

5fill in blank

hard

Fill all three blanks to implement a cache with expiration, lock, and fallback to stale data.

HLD

if cache_data is None or cache_timestamp [1] current_time:
    if cache_lock.[2]():
        fresh_data = fetch_data()
        cache_store.[3](cache_key, fresh_data)
    else:
        use_stale_cache()

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

A<

Bacquire

Cset

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' for expiration check.

Not acquiring lock before cache update.

We check if cache expired with '<'. Then we acquire the lock to refresh cache. Finally, we set fresh data in cache. If lock not acquired, fallback to stale cache.