An organization has deployed a multi-region Cloud Spanner instance for a global application. The application is experiencing high latency for read requests from a specific region. The team has verified that the application is using stale reads and the data distribution is even. What is the most likely cause of the high latency?
Adding a read replica in the region reduces network round-trip time, lowering read latency.
Why this answer
Cloud Spanner uses a single global configuration with regional read replicas. If the instance does not have a read replica in the region where the clients are located, read requests must traverse the network to a replica in another region, causing higher latency. Even with stale reads, the physical distance to the nearest replica directly impacts read latency.
Exam trap
Google Cloud often tests the misconception that adding more nodes or read replicas solves regional latency, when the real issue is the absence of a local replica in the specific region.
How to eliminate wrong answers
Option A is wrong because Cloud Spanner does not have a concept of 'read replicas' in the same way as traditional databases; it uses a single set of nodes per instance, and read capacity scales with the number of nodes, not with separate read replicas. Option B is wrong because the team has verified that data distribution is even, and the question states the issue is specific to a region, not global contention; too few nodes would cause high latency across all regions, not just one. Option C is wrong because the team has already verified that the application is using stale reads, which are read-only transactions by definition; read-write transactions would not be used in this scenario.