What is the Spanner emulator?

The Cloud Spanner emulator is a local, in-memory version of Spanner that implements the same gRPC API as the production service, letting developers write and test code without connecting to a real instance or incurring cost.

gcloud emulators spanner start
gcloud config set auth/disable_credentials true
gcloud config set api_endpoint_overrides/spanner http://localhost:9020/

It supports DDL, DML, mutations, and transactions, making it suitable for unit tests and CI pipelines. It does not enforce real replication, TrueTime uncertainty, or performance characteristics, so latency-sensitive or scale-related behavior still needs to be validated against a real instance before production rollout.

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