When using Cloud Spanner, which of the following is not an advisable way to ensure optimal performance?

*Explanation:* In the context of Cloud Spanner, while denormalizing data (option A. , interleaving tables (option B. , properly sharding your data with a good primary key (option D), and using secondary indexes (option E) are advisable strategies to ensure optimal performance, **using complex joins (option C. ** is not recommended. Cloud Spanner is optimized for schemaless, horizontally scaled, and globally distributed data, and it performs best when queries can be resolved without complex joins. Using complex joins can lead to decreased query performance and should be avoided.