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What is the difference between absolute expiration and sliding expiration when configuring a cache entry?

Intermediate

Answer

Absolute expiration removes an entry at a fixed point in time regardless of how recently it was accessed, guaranteeing data won't become stale beyond a hard limit. Sliding expiration resets the expiration timer every time the entry is accessed, keeping frequently-used data cached indefinitely while letting rarely-used entries expire -- the two can be combined to set both a 'refresh on access' behavior and a hard maximum lifetime.
_cache.Set("key", value, new MemoryCacheEntryOptions {
    SlidingExpiration = TimeSpan.FromMinutes(5),      // resets on each access
    AbsoluteExpirationRelativeToNow = TimeSpan.FromHours(1)  // hard cap regardless
});
Real-world example A frequently-accessed user session cache uses a 5-minute sliding expiration combined with a 1-hour absolute cap, so active users keep their cached session alive while inactive sessions are forcibly cleared within an hour at most.

Common follow-ups: What happens if only sliding expiration is set with no absolute cap?;How does cache eviction interact with memory pressure signals?

Diagnostics & Performance;Authentication & Authorization (Identity JWT OAuth)
All 15 Caching (In-Memory, Distributed & Redis) questions