Exam DP-420 topic 1 question 41 discussion

Actual exam question from Microsoft's DP-420

Question #: 41
Topic #: 1

Your company develops an application named App1 that uses the Azure Cosmos DB SDK and the Eventual consistency level.

App1 queries an Azure Cosmos DB for NoSQL account named account1.

You need to identify which consistency level to assign to App1 to meet the following requirements:

• Maximize the throughput of the queries generated by App1 without increasing the number of request units currently used by the queries.
• Provide the highest consistency guarantees.

Which consistency level should you identify?

A. Strong
B. Bounded Staleness
C. Session
D. Consistent Prefix

Show Suggested Answer

Suggested Answer: D 🗳️

by SwePha at Nov. 12, 2023, 8:41 p.m.

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matejka

4 months, 3 weeks ago

Selected Answer: C

Throughput Optimization: Session consistency offers a balance between strong consistency and high throughput, which makes it a good option for applications that require predictable performance without significantly increasing the Request Unit (RU) cost. Highest Consistency Guarantees: Among the weaker consistency levels (below Strong and Bounded Staleness), Session consistency provides strong consistency guarantees within the session context of a single user. It ensures monotonic reads, monotonic writes, and read-your-own-writes for requests within the same session. While Strong (A) and Bounded Staleness (B) offer higher consistency guarantees than Session, they tend to use more RUs, potentially reducing throughput. Eventual (default) and Consistent Prefix (D) have higher throughput but offer weaker consistency guarantees compared to Session.

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szkielet

6 months ago

Selected Answer: D

Consistent Prefix: Consistent prefix guarantees that all reads will see writes in the order they were made. It's the strongest consistency level that still allows for high throughput. It's stronger than session consistency because it guarantees global ordering of writes, not just within a session.

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biglebowski88

7 months, 3 weeks ago

Selected Answer: D

Consistent prefix will not increase the RU consumption whilst providing better consistency guarantee than session and eventual. the other two increase RU consumption and therefore incorrect.

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[Removed]

11 months ago

Selected Answer: D

For strong and bounded staleness, reads are done against two replicas in a four replica set (minority quorum) to provide consistency guarantees. Session, consistent prefix and eventual do single replica reads. The result is that, for the same number of request units, read throughput for strong and bounded staleness is half of the other consistency levels. https://learn.microsoft.com/en-us/azure/cosmos-db/consistency-levels#consistency-levels-and-throughput

upvoted 2 times

[Removed]

9 months, 1 week ago

This is true, however, Session also does single replica reads and is stronger compared to consistent prefix, so why is it not chosen as an answer?

upvoted 3 times

biglebowski88

7 months, 2 weeks ago

I think because session consistency only provides that consistency strength in the context of a user session so its a bit of an outlier. I dont think we can take that hierarchy at face value as it depends on the context. bit of a weird question without more context.

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biglebowski88

7 months, 2 weeks ago

Session falls back to Eventual for data that is written by someone else apparently . so consistent prefix is definitely the best option for all round consistency and without impacting RUs

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xRiot007

1 year ago

Answer is D - Consistent preffix. Why ? We need to provide the highest consistency guarantees without decreasing throughput. Strong and bounded staleness provide half the throughput of Session, Consistent Prefix and Eventual, so by choosing them you decrease the throughput.

upvoted 3 times