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Question 196 of 1,446

PCDE Practice Question: Manage a solution that can span multiple database technologies

A Memorystore for Redis instance is running out of memory. The application uses a mix of cache and session data. Which eviction policy should be chosen to minimize cache misses while ensuring session data is not evicted?

⚠ Common exam trap

The PCDOE exam often tests the misconception that allkeys-lru is always the best for cache performance, but here the requirement to protect session data makes volatile-ttl the correct choice because it only evicts keys with TTLs, allowing session data to be preserved by setting a longer TTL.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

volatile-ttl

The volatile-ttl policy evicts keys with a TTL set, prioritizing those with the shortest remaining TTL. Since session data typically has a TTL and cache data may or may not, this policy allows you to protect session data by assigning it a longer TTL, while cache data with shorter TTLs is evicted first, minimizing cache misses.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • noeviction

    Why it's wrong here

    Returns errors on writes once memory full, likely causing application failures.

  • volatile-ttl

    Why this is correct

    Evicts only keys with TTL set (cache), leaving session data (no TTL) intact.

  • allkeys-lru

    Why it's wrong here

    This evicts any key (including sessions) based on LRU, which could cause session loss.

  • allkeys-random

    Why it's wrong here

    Random eviction could remove session data and is not efficient for cache.

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Last reviewed: Jul 4, 2026

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