React cache() vs Next.js Fetch Deduplication Operate at Different Layers

cache() and Next.js's automatic fetch deduplication are the same underlying mechanism, so the database call is deduplicated identically to a fetch call.

cache() memoizes a function's return value per render pass within a single server request for any data source — so the database call is correctly deduplicated — but that happens because cache() itself is generic, not because Next.js's fetch-level deduplication (which only intercepts the global fetch function) applies to it.

Database calls cannot be deduplicated at all in Server Components; only calls made through the global fetch function benefit from either mechanism.

cache() only memoizes a function if that function internally calls fetch, so a raw database client call silently bypasses memoization entirely.