Your company has an internal application for managing transactional orders. The application is used exclusively by employees in a single physical…

The application is built on PostgreSQL and requires a cloud migration with minimal code changes. Cloud SQL is a fully managed relational database service that offers a PostgreSQL engine. This makes it the most suitable choice as it allows for a direct migration path, often referred to as "lift and shift." Cloud SQL provides the necessary strong consistency and full ACID compliance for transactional workloads, which are explicitly required by the order management application. Its regional nature is appropriate for an application used by employees in a single location.

A. BigQuery is a serverless data warehouse designed for large-scale data analytics (OLAP), not for transactional (OLTP) applications that require frequent updates and ACID guarantees.
C. Cloud Spanner is a globally distributed, horizontally scalable database. Migrating from PostgreSQL to Spanner would require significant application changes, violating the "minimal code changes" constraint.
D. Cloud Datastore (Firestore in Datastore mode) is a NoSQL document database. Migrating a relational application from PostgreSQL would necessitate a complete application rewrite.

1. Google Cloud Documentation - Cloud SQL: "Cloud SQL is a fully managed relational database service for MySQL

PostgreSQL

and SQL Server. ... It's a good fit for any application that requires a relational database

such as customer relationship management

enterprise resource planning

or e-commerce applications." This aligns with the transactional order management use case.

Source: Google Cloud

"Cloud SQL for PostgreSQL overview

" Section: "What is Cloud SQL for PostgreSQL?".

2. Google Cloud Documentation - Choosing a Database: A table comparing database options shows Cloud SQL is ideal for "Web frameworks

OLTP systems" and notes its "Familiarity (MySQL

PostgreSQL

SQL Server)." In contrast

it positions Spanner for "High-throughput OLTP

global scale

" BigQuery for "Data warehousing

analytics

" and Datastore for "App backends

semi-structured data."

Source: Google Cloud

"Choose a database option

" Section: "Summary of Google Cloud database options".

3. Google Cloud Documentation - Cloud Spanner: "Spanner is not a drop-in replacement for other relational database systems. You might need to adapt your application's logic to get the most out of Spanner's features." This confirms that migrating from PostgreSQL would not involve minimal changes.

Source: Google Cloud

"Spanner: A global

mission-critical database

" Section: "When to use Spanner".