An application team is preparing a global rollout. Three architectural decisions are still open: whether to deploy the database in a single region or replicate it across regions; whether to introduce an application-level cache; and what cache invalidation strategy to use if the cache is added. The team's most important requirement is that account balances must always show the exact current value to any user. Considering this requirement, the most appropriate combination is:

Question

Accepted Answer

Single-region database with write-through caching for balance values, and routing of all balance reads to the primary database itself rather than to any read replica that might lag behind it.

Answer

Single-region database with no caching of balances at all, since any cache layer is fundamentally incompatible with the requirement that balance values be exactly current.

Answer

Replicated database with an aggressive write-back cache for balances, because faster writes will improve the user experience even if the cache occasionally lags behind the database.

Answer

Replicated database with a long TTL cache on balance values, because long TTLs maximize the cache hit rate and reduce overall energy consumption across the system.

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An application team is preparing a global rollout. Three architectural decisions...

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