Exam AWS Certified Data Analytics - Specialty topic 1 question 86 discussion

Exam question from Amazon's AWS Certified Data Analytics - Specialty

Question #: 86
Topic #: 1

[All AWS Certified Data Analytics - Specialty Questions]

A large retailer has successfully migrated to an Amazon S3 data lake architecture. The company's marketing team is using Amazon Redshift and Amazon
QuickSight to analyze data, and derive and visualize insights. To ensure the marketing team has the most up-to-date actionable information, a data analyst implements nightly refreshes of Amazon Redshift using terabytes of updates from the previous day.
After the first nightly refresh, users report that half of the most popular dashboards that had been running correctly before the refresh are now running much slower. Amazon CloudWatch does not show any alerts.
What is the MOST likely cause for the performance degradation?

A. The dashboards are suffering from inefficient SQL queries.
B. The cluster is undersized for the queries being run by the dashboards.
C. The nightly data refreshes are causing a lingering transaction that cannot be automatically closed by Amazon Redshift due to ongoing user workloads.
D. The nightly data refreshes left the dashboard tables in need of a vacuum operation that could not be automatically performed by Amazon Redshift due to ongoing user workloads.

Show Suggested Answer

Suggested Answer: D 🗳️

by bermo at May 1, 2021, 2:15 p.m.

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VikG12

Highly Voted 3 years, 8 months ago

Looks like it's D. https://github.com/awsdocs/amazon-redshift-developer-guide/issues/21

upvoted 23 times

lakediver

3 years, 5 months ago

Agree for further reading please see https://aws.amazon.com/about-aws/whats-new/2018/12/amazon-redshift-automatic-vacuum/

upvoted 4 times

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pk349

Most Recent 2 years, 1 month ago

D: I passed the test

upvoted 1 times

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cloudlearnerhere

2 years, 7 months ago

Correct answer is D as the reason for the drop in query performance might because of the long nightly data refreshes operation which blocked the vacuum operation and left it in the need of the vacuum operation. Amazon Redshift can automatically sort and perform a VACUUM DELETE operation on tables in the background. To clean up tables after a load or a series of incremental updates, you can also run the VACUUM command, either against the entire database or against individual tables. A vacuum operation might not be able to start if a load or insert operation is already in progress. Vacuum operations temporarily require exclusive access to tables in order to start. This exclusive access is required briefly, so vacuum operations don't block concurrent loads and inserts for any significant period of time.

upvoted 4 times

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lygf

2 years, 8 months ago

Selected Answer: D

C. if there is a lingering transaction, it will block other read queries or transactions. The Question said the next day query ran slow, not being blcoked, so C is out.

upvoted 1 times

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arboles

2 years, 10 months ago

Selected Answer: D

A is always can be but as fas as it worked before night transaction A and B is out. C is rear case because typically transactions block dara read and not making redshift slower( due to wlm and queues it hardly a case) after any DML or DDL operation there is a lot of junk an need of vacume, During vacuum there can be seom perfomance issue for queries that tryes to use that table that is why redshift autowacuum doesn't start when there is high user activity. So we need to vacuum explisitly to make things faster.

upvoted 1 times

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rocky48

2 years, 10 months ago

Selected Answer: D

Correct Answer is D

upvoted 1 times

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certificationJunkie

3 years ago

C sounds correct answer. It could be between C and D. But considering Redshift automatically vacuumes the tables periodically, and that user work load is the reason for the slowness, I would pick C over D.

upvoted 1 times

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