Scan vs. Query Exam Tips

• A Query operation finds items in a table using only the Primary Key attribute.
• You provide the Primary Key name and a distinct value to search for.
• A Scan operation examines every item in the table.
• By default, returns all data attributes
• Use the ProjectionExpression parameter to refine the results
• Query results are always sorted by the Sort Key, if there is one.
• Sorted in ascending order.
• Set ScanIndexForward parameter to false to reverse the order (Queries only).
• Query operation is generally more efficient than a Scan.
• Reduce the impact of query or scan by setting a smaller page size, which uses fewer read operations and/or by running parallel scans
• Isolate scan operations to specific tables and segregate them from your mission-critical traffic.
• Try Parallel scans, rather than the default sequential scan.
• Avoid using scan operations if you can. Design tables in a way that you can use the Query, Get, or BatchGetItem APIs.
• BatchGetItem is used to retrieve multiple items from a DynamoDB table.
• Remember Scan returns everything (not filtered down by Partition Key)