Exam AWS Certified Database - Specialty topic 1 question 146 discussion

Exam question from Amazon's AWS Certified Database - Specialty

Question #: 146
Topic #: 1

[All AWS Certified Database - Specialty Questions]

An online advertising website uses an Amazon DynamoDB table with on-demand capacity mode as its data store. The website also has a DynamoDB Accelerator
(DAX) cluster in the same VPC as its web application server. The application needs to perform infrequent writes and many strongly consistent reads from the data store by querying the DAX cluster.
During a performance audit, a systems administrator notices that the application can look up items by using the DAX cluster. However, the QueryCacheHits metric for the DAX cluster consistently shows 0 while the QueryCacheMisses metric continuously keeps growing in Amazon CloudWatch.
What is the MOST likely reason for this occurrence?

A. A VPC endpoint was not added to access DynamoDB.
B. Strongly consistent reads are always passed through DAX to DynamoDB.
C. DynamoDB is scaling due to a burst in traffic, resulting in degraded performance.
D. A VPC endpoint was not added to access CloudWatch.

Show Suggested Answer

Suggested Answer: B 🗳️

by grekh001 at Oct. 25, 2021, 1:59 p.m.

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grekh001

Highly Voted 3 years, 8 months ago

B is correct. https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DAX.concepts.html "If the request specifies strongly consistent reads, DAX passes the request through to DynamoDB. The results from DynamoDB are not cached in DAX. Instead, they are simply returned to the application."

upvoted 6 times

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Pranava_GCP

Most Recent 1 year, 8 months ago

Selected Answer: B

B. Strongly consistent reads are always passed through DAX to DynamoDB.

upvoted 1 times

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lollyj

2 years, 5 months ago

Selected Answer: B

My thoughts - if strongly consistency reads are requested it will pass through DAX to the DB.

upvoted 1 times

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novice_expert

3 years, 1 month ago

Selected Answer: B

strong consistency => bypass DAX

upvoted 3 times

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RotterDam

3 years, 3 months ago

Selected Answer: B

Strongly Consistent Reads are considered PASS THROUGH and will never update DAX Interestingly - TransactionGetItems is also a PASS THROUGH but TransactionWriteItems is not!!

upvoted 2 times

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kped21

3 years, 3 months ago

B: If the request specifies eventually consistent reads (the default behavior), it tries to read the item from DAX: If DAX has the item available (a cache hit), DAX returns the item to the application without accessing DynamoDB. If DAX does not have the item available (a cache miss), DAX passes the request through to DynamoDB. When it receives the response from DynamoDB, DAX returns the results to the application. But it also writes the results to the cache on the primary node. If the request specifies strongly consistent reads, DAX passes the request through to DynamoDB. The results from DynamoDB are not cached in DAX. Instead, they are simply returned to the application.

upvoted 3 times

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