How do Redis eviction policies like allkeys-lru versus volatile-ttl change your cache design?
PICTURE THIS: RAG CHATBOT
Simple meaning
allkeys-lru evicts any key under memory pressure, so even locks and sessions can vanish unless they are tiny and you size Redis for them.
WHY — Redis instead of guessing?
Why interviewers care about Redis:
contrast on Redis, not two memorised paragraphs.
the developer, then one case where picking wrong hurts.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1allkeys-lru evicts any key
under memory pressure, so even locks and sessions can vanish unless they are tiny and you size Redis for them.
- 2volatile-lru/ttl only evicts keys
that have a timeout, protecting keys you set without TTL.
- 3Product rule: never store
must-not-lose data only in an LRU cache.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
allkeys-lru evicts any key under memory pressure, so even locks and sessions can vanish unless they are tiny and you size Redis for them. volatile-lru/ttl only evicts keys that have a timeout, protecting keys you set without TTL.