All 15 Caching (In-Memory, Distributed & Redis) questions
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What is IMemoryCache, and when is it appropriate to use for caching in ASP.NET Core?

Beginner

Answer

IMemoryCache is a built-in in-process cache storing key-value pairs directly in the application's own memory, ideal for single-instance applications or data that's acceptable to recompute per-instance -- it's extremely fast (no network round-trip) but not shared across multiple server instances, and its contents are lost on application restart.
builder.Services.AddMemoryCache();

public class ProductService {
    private readonly IMemoryCache _cache;
    public ProductService(IMemoryCache cache) => _cache = cache;

    public async Task<Product> GetProductAsync(int id) {
        return await _cache.GetOrCreateAsync($"product-{id}", async entry => {
            entry.SlidingExpiration = TimeSpan.FromMinutes(10);
            return await _repository.GetByIdAsync(id);
        });
    }
}
Real-world example A single-instance internal reporting tool caches expensive aggregate query results in IMemoryCache for 10 minutes, dramatically reducing database load for a report viewed repeatedly by the same handful of users.

Common follow-ups: What's the memory pressure risk of IMemoryCache with unbounded growth?;How does IMemoryCache differ across multiple load-balanced server instances?

Diagnostics & Performance;Configuration & Options
All 15 Caching (In-Memory, Distributed & Redis) questions