DynamoDB Consistency Models Quiz Quiz

Explore the fundamental principles and behaviors of DynamoDB consistency models with this quiz. Assess your grasp of eventual and strong consistency, read and write operations, and how consistency impacts performance and data accuracy.

1. Consistency Model Basics

   Which consistency model guarantees that a read returns the most recently written value for a data item?

   1. Causal consistency
   2. Base consistency
   3. Strongly consistent read
   4. Eventual consistency

   Explanation: Strongly consistent reads guarantee that a read will always return the latest value as soon as a write is acknowledged. Eventual consistency does not provide this guarantee and may return stale data. Causal consistency and Base consistency are not the standard terms for read consistency choices in this context. Strongly consistent reads are selected when immediate accuracy is necessary.

2. Default Consistency Behavior

   What is the default read consistency offered by DynamoDB when no specific option is set?

   1. Immediate consistency
   2. Linear consistency
   3. Strongly consistent read
   4. Eventual consistency

   Explanation: The default read consistency is eventual consistency, which allows for higher availability and scaling but may return stale data. Immediate consistency and linear consistency are not official consistency levels and do not describe the actual default. Strongly consistent read is an optional choice, not the default.

3. Use Case for Eventual Consistency

   Which scenario is most appropriate for using eventual consistency?

   1. When consistency must be enforced across multi-region writes
   2. When every user must always see the latest version of data
   3. When strict transaction isolation is mandatory
   4. When delayed updates are acceptable in return for faster reads

   Explanation: Eventual consistency is suitable when applications can tolerate reading slightly out-of-date data in exchange for better performance and availability. If every user must see the latest data or strict isolation is required, strongly consistent or transactional options should be chosen. Multi-region consistency is also not addressed by eventual consistency.

4. Consistency and Read Latency

   How does using strong consistency affect read latency compared to eventual consistency?

   1. Both have identical read latencies
   2. Strong consistency generally has higher read latency
   3. Strong consistency always has lower read latency
   4. Strong consistency disables all network delays

   Explanation: Strong consistency often incurs higher latency because it ensures the read reflects all successful writes. Eventual consistency can return faster by not guaranteeing the newest value. The latencies are not always identical, and strong consistency cannot disable network delays.

5. Consistency in Reads versus Writes

   Which statement is true about write consistency in comparison to read consistency?

   1. Both reads and writes are always strongly consistent
   2. Writes are always strongly consistent in DynamoDB
   3. Writes can be eventually consistent, but reads are always strongly consistent
   4. Reads can be either strong or eventual, but writes are always eventually consistent

   Explanation: All successful write operations are strongly consistent, ensuring the data is fully committed. Reads, however, can be chosen as either strongly or eventually consistent. The other options incorrectly describe the available consistency options for writes.

6. Global Secondary Index Consistency

   What type of consistency is always used when reading from a global secondary index?

   1. Immediate consistency
   2. Strong consistency
   3. Eventual consistency
   4. Local consistency

   Explanation: Reads from global secondary indexes are always eventually consistent, meaning they may not reflect the most recent updates instantly. Strong consistency and immediate consistency are not options for this scenario. Local consistency is not an actual consistency type.

7. Choosing Read Consistency

   When designing a system that requires users to always see the latest updates immediately after writing, which read consistency option should be selected?

   1. Eventual consistency
   2. Weak consistency
   3. Partial consistency
   4. Strongly consistent read

   Explanation: Selecting strongly consistent reads ensures fresh data is always returned. Eventual, weak, and partial consistency types may occasionally return stale values, which is not acceptable for this use case. Only strong consistency fulfills the requirement.

8. Multi-region Consistency Implications

   If a data store is configured in multiple geographically separated locations, what consistency level might result in reading old data shortly after a write?

   1. Instant consistency
   2. Eventual consistency
   3. Hard consistency
   4. Strict consistency

   Explanation: Eventual consistency can lead to stale reads right after writes, especially across distributed locations. Strict, hard, and instant consistency are not recognized terms in this context, and would not permit such staleness in theory.

9. Cost of Strong Consistency

   What is one impact of choosing strong consistency for reads over eventual consistency?

   1. Strong consistency always allows stale data
   2. Strong consistency lowers the cost per read
   3. Strong consistency guarantees unlimited throughput
   4. Stronger consistency may increase resource consumption and cost

   Explanation: Strongly consistent reads require more coordination and can increase resource usage and associated costs. It does not lower costs, permit old data, or guarantee unlimited throughput, as those descriptions are inaccurate with respect to strong consistency.

10. Consistency in Batch Operations

    When performing a batch read operation, what consistency model is applied to batch items?

    1. Each item in the batch can be individually consistent, but overall batch consistency is not guaranteed
    2. Batch reads prevent stale reads
    3. Every item in the batch has guaranteed strong consistency
    4. Batch reads always enforce transactional consistency

    Explanation: In batch operations, each item is read individually with the chosen consistency, but there is no guarantee across the overall set. Strong or transactional consistency is not ensured for the batch as a whole, and batch reads can still return stale data if eventual consistency is used.