AWS Certified Data Engineer Associate DEA-C01 Practice Question

Storing all of a user's cart items under the same partition key lets the application fetch or update the complete cart with one strongly consistent Query operation. Making userId the partition key and an ever-increasing attribute such as addedAt the sort key groups those items together while preserving ordering. A global secondary index (GSI) whose partition key is productId provides an efficient access path for the much less frequent query that aggregates the same product across many users. TTL on expiresAt removes stale items automatically at no extra read/write cost and does not affect either access pattern. Scanning the base table, using productId as the primary key (which would require a scan for user carts), or relying on a local secondary index (which cannot use a different partition key) would all raise costs or fail to meet one of the query requirements.