4 Amazon DynamoDB in Practice Free Online FlashCards

What should guide a DynamoDB table design?

List the application’s reads and writes first, then choose keys and indexes that make those access patterns efficient direct lookups or queries.

What do the partition key and sort key do?

The partition key locates an item collection. Items sharing it can be queried together, and the sort key orders items within that collection.

Why add an order ID after a timestamp in a sort key?

Consistently formatted ISO 8601 date strings sort chronologically as strings. Adding an order ID makes sort keys distinct when timestamps match.

How do a GSI and an LSI differ in their keys?

A GSI can use a different partition key and sort key from the table. An LSI keeps the table’s partition key but uses an alternate sort key.

When must an LSI be specified?

An LSI must be specified when the table is created; a GSI can be added later.

Why should DynamoDB indexes be added selectively?

Indexes add storage and write work because indexed items maintain their index entries. Project only the attributes needed for queries, and add indexes for real access patterns.

How can a GSI be made sparse?

A GSI is sparse when only items with its index key attributes are included. Omitting those attributes can make the index query only a desired subset.

How do GetItem and Query differ?

GetItem retrieves an item by its full primary key. Query matches one partition-key value and can also constrain the sort key.

Why doesn’t a filter expression make a broad query efficient?

A filter expression removes items after DynamoDB reads them, so it does not make a broad query efficient. Put frequently used selection criteria in keys when practical.

How do you continue a paginated Query or Scan?

A Query or Scan response is limited to 1 MB per request. If LastEvaluatedKey is present, pass it as ExclusiveStartKey to continue.

Can a page return no items and still require pagination?

Yes. A filter can remove every returned item on a page while LastEvaluatedKey still indicates that more data remains.

What makes Scan costly for routine lookups?

Scan reads every item in a table or index before applying any filter. It suits small datasets or genuine full traversals, but is usually a poor substitute for a queryable design.