Exam AZ-204 topic 5 question 33 discussion

Changed my mind; There must be a way to tell our redis that logged off users must not be prioritized. Sample: User A moves and then automatically logs-off. With allkeys-lru we can't distinguish this particularity. With volatile-lru we can tell our redis what are good candidates to be removed using different TTL values.

I still don't understand the advantage of volatile-lru over allkeys-lru in this case. The key in redis is updated when the user moves, not when the user logs in or out. So even with a TTL, a user who is still logged, but hasn't moved in a long time can have an older key compared to a recently logged out user that has just moved before logging out. With that said, and even if a TTL is set when the user moves, chosing volatile-lru will not prioritize logged in users. And as the question doesn't state a TTL is set, all keys need to be evicted (those with TTL and those without). With volatile-lru eviction keys without TTL would be prioritized, but that would mean some users would have their position stored with TTL and some without. That distinction doesn't make sense. So, although B can work, without knowing fore sure we are storing keys with a TTL, A is the safest option.

B. volatile-lru

volatile-lru makes sense because setting a short TTL, will deprioritize logged out players quicker than allkeys-lru. This question is very tricky tough

Skip all the assumptions. Doesn't '...and should not prioritize players who have logged out of the game.' mean that we don't look at ttl or make any other changes to the key. Just use 'how recently they have moved', i.e. last recently used. I agree with raymond_abcd. -> A. allkeys-lru.

The default TTL for Redis is infinite, so for volatile-lru to be the correct answer, the config must have the TTL set to some expiration value. Nothing is mentioned in the question about TTL. So it doesn't seem likely that this is the correct answer.

volatile-lru: This policy also evicts the least recently used keys but only among those with a set TTL(time to live). Keys without a TTL are not considered for eviction. This policy could be appropriate if you set a TTL for players' data and reset or update this TTL when they move. Players who log out can have their TTL removed or expired, making them ineligible for eviction under this policy.

I vote for allkeys-Iru. volatile-Iru is helpful to deal with or correlate a concept with expiration time. We have the cache of recent players, and what they do then (for example, logging off) does not affect the eviction policy.

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There's no link with ttl and players who have logged out of the game. In Redis, you can set the TTL (Time To Live) for keys using commands such as EXPIRE, PEXPIRE, or similar commands that allow you to specify a lifespan for a key. The TTL specifies the period for which the key will be retained in the Redis database before being automatically removed.

I think the answer is correct. We can remove the related entry from the cache after logoff or simply grab the next entry from the cache if the user is inactive. Volatile policies could even prevent caching, see https://redis.io/docs/reference/eviction/ The policies volatile-lru, volatile-lfu, volatile-random, and volatile-ttl behave like noeviction if there are no keys to evict matching the prerequisites.

Think it should be B : volatile-lru volatile-lru : Removes least recently used keys with the expire field set to true. The expire field for the logged out players can be marked true indicating Redis to evict those entries

ChatGPT answer option is volatile-ttl

Got this 2023-05-12. Had cases: case: You need to configure authorization. case: You need to ensure the app does not time out and processes the blob data case study: VanArsdel Inc Canada

The "volatile-ttl" eviction policy evicts keys based on their expiration time, which is set when the key is created or updated. This policy is the most suitable for this scenario since it allows the system to prioritize recently moved players by setting a shorter expiration time for their cached location data. It also ensures that players who have logged out of the game are automatically removed from the cache when their data expires. Chat GPT

allkeys-lru: Keeps most recently used keys; removes least recently used (LRU) keys volatile-lru: Removes least recently used keys with the expire field set to true. Source: https://redis.io/docs/reference/eviction/ Not prioritizing logged off players does not mean to remove them! volatile-lru will not be the best solution at all.

I think it is A because I don't understand the need to be restricted to only entries with TTL.