The correct answer is Online Transaction Processing (OLTP). This retail application performs frequent short reads and writes against a relational Cloud SQL instance to process orders and update customer records which matches the characteristics of OLTP.

OLTP workloads emphasize many small, concurrent transactions with low latency and strong consistency. A relational Cloud SQL instance is designed for these kinds of transactional operations where ACID guarantees and fast updates to customer and order data are required.

Stream processing is not correct because it focuses on continuous processing of event streams and real time analytics rather than the many small, transactional updates to a relational database that this scenario describes.

Online Analytical Processing (OLAP) is not correct because OLAP is optimized for complex, large scale analytical queries and reporting over historical data rather than low latency transactional reads and writes to update current records.

Batch processing is not correct because batch jobs run on large sets of data at scheduled intervals and are not suited for the immediate, per-transaction updates needed to process orders and keep customer records current.

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