Practice Test

True or False: Both query and scan operations are used to retrieve data in Amazon DynamoDB.

  • True
  • False

Answer: True.

Explanation: Both operations are used to retrieve data from a DynamoDB table but they differ in the way they access and return the data.

Which operation is faster: query or scan?

  • a) Scan
  • b) Query
  • c) Both are equally fast
  • d) It depends on the data

Answer: b) Query

Explanation: Query is faster as it uses a direct method to access data, while Scan scans the entire table before returning the data.

True or False: Scan operations have a higher cost than Query operations.

  • True
  • False

Answer: True.

Explanation: A Scan operation reads every item in a table, which can be costly in terms of performance and pricing, while a Query reads only the targeted items, reducing costs.

What’s a key difference between query and scan operations in AWS DynamoDB?

  • a) Query operation searches the entire table, while Scan operation only searches a specific segment
  • b) Query operation uses filters while Scan operation does not
  • c) Scan operation can retrieve all items, while Query operation must specify a partition key value
  • d) Scan operation cannot be stopped once started, while Query operation can

Answer: c) Scan operation can retrieve all items, while Query operation must specify a partition key value

Explanation: Scan operation retrieves all the table data, query operation needs a specific value of the primary key.

True or False: A scan operation always checks every item in the table.

  • True
  • False

Answer: True.

Explanation: A Scan operation on a table or an index scans the entire table or index and returns all of the data.

Which operation allows multiple conditions:

  • a) Scan
  • b) Query
  • c) Both
  • d) Neither

Answer: c) Both

Explanation: Both scan and query operations can use multiple conditions, but a query requires at least one equality condition that can be satisfied by a partition key.

True or False: The query operation in DynamoDB retrieves data by using a secondary index.

  • True
  • False

Answer: True.

Explanation: In DynamoDB, you can use secondary indexes to speed up queries, by creating a data structure that can directly satisfy the query.

What method does the scan operation use to retrieve data?

  • a) Scans the whole table
  • b) Direct access
  • c) Through an index
  • d) It does not retrieve data

Answer: a) Scans the whole table

Explanation: Scan scans the entire table and then filters out data to return what is requested.

True or False: A Scan operation in DynamoDB is always more efficient than a Query operation.

  • True
  • False

Answer: False.

Explanation: Scan operations can be much less efficient than Query operations, as they must read every item in the table.

What is a key constraint of a Query operation in DynamoDB?

  • a) It cannot use multiple filters
  • b) It must specify a partition key value
  • c) It cannot retrieve multiple items
  • d) It cannot specify a partition key value

Answer: b) It must specify a partition key value.

Explanation: A Query operation finds items based on primary key values, and to perform a query, you must specify a partition key value.

Which operation in DynamoDB consumes fewer read units?

  • a) Query
  • b) Scan
  • c) Both consume the same amount
  • d) Cannot be determined

Answer: a) Query

Explanation: A scan operation reads every item in the table, consuming more read capacity units.

True or False: A Scan operation in DynamoDB cannot use Filter Expressions.

  • True
  • False

Answer: False.

Explanation: Both Scan and Query operations can use Filter Expressions in DynamoDB.

In DynamoDB, what is the primary reason for using a Query operation over a Scan operation?

  • a) Cost-effectiveness
  • b) Speed
  • c) Filters
  • d) All of the above

Answer: d) All of the above

Explanation: Query operations are generally faster, more cost-effective and allow more specific data retrieval than Scan operations.

True or False: Query and Scan operations in DynamoDB have the same return limits.

  • True
  • False

Answer: True.

Explanation: Both Query and Scan operations will only return a maximum of 1MB of data.

Is the Scan operation efficient for large DynamoDB tables?

  • a) Yes
  • b) No
  • c) It depends on the table structure
  • d) It depends on the number of items in the table

Answer: b) No

Explanation: For large tables, a Scan operation can be expensive in terms of system resources and network communications, as it reads every single item.

Interview Questions

What is a query operation in AWS DynamoDB?

A Query operation in DynamoDB finds items in a table using the primary key attribute and a distinct value to search for.

What is a scan operation in DynamoDB?

A Scan operation in DynamoDB reads every item in a table or a secondary index.

Which operation, query or scan, is less efficient in terms of time and reads?

Scan operation is less efficient because it reads every item in a table or index and can use up a lot of read capacity.

How does a query operation work in DynamoDB?

A query operation uses the table’s primary key or a secondary index’s key attributes to get items with a specific attribute value. You can use optional parameters to filter the results.

How does a scan operation work in DynamoDB?

A scan operation reads every item in a table or secondary index. As the scan operation must scan the entire table, it can consume a lot of read capacity units.

Can the scan operation in DynamoDB return every attribute for every item?

Yes, by default, a scan operation in DynamoDB returns all data attributes for every item. However, you can use the ProjectionExpression parameter to refine the attributes that are returned.

Are query operations in DynamoDB always faster than scan operations?

Query operations in DynamoDB are usually faster and use fewer read capacity units than scan operations, as scan operations examine every item in the table or index.

Is the scanning operation in DynamoDB always slower than a query operation?

Yes, because a scan operation in DynamoDB examines every item in the table or index, it’s usually slower and requires more read capacity units than a query operation.

Can you filter the results of a query operation in DynamoDB?

Yes, query results in DynamoDB can be filtered with additional criteria using the FilterExpression parameter.

Can you filter the results of a scan operation in DynamoDB?

Yes, scan results in DynamoDB can also be filtered with the FilterExpression parameter.

What are the main efficiency considerations when choosing between a query and a scan operation in DynamoDB?

The main efficiency considerations include the amount of data you need, the detail of that data, read capacity consumption, and execution speed.

How can the efficiency of a scan operation be improved in DynamoDB?

Scan operation efficiency can be improved in DynamoDB by using parallel scans or setting page size limits. Limiting the returned attributes with the ProjectionExpression parameters can also increase efficiency.

When should you use a query operation over a scan operation in DynamoDB?

If you need to retrieve items based on a specific attribute value, it’s more efficient to use a Query operation. Query operations are faster and use fewer read capacity units than scan operations.

Can both query and scan operations in DynamoDB operate on secondary indexes?

Yes, both query and scan operations can operate on both table data and secondary indexes in DynamoDB.

Why might scan operations in DynamoDB lead to throttling?

Because scan operations read every item in a table or an index, they can quickly consume read capacity. If the operations exceed the table or index’s provisioned read capacity, DynamoDB may throttle them to prevent disrupting other workloads.

Leave a Reply

Your email address will not be published. Required fields are marked *