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Exam MCD - Level 1 topic 1 question 65 discussion

Actual exam question from Mulesoft's MCD - Level 1

Question #: 65
Topic #: 1

A Database On Table Row listener retrieves data from a CUSTOMER table that contains a primary key user_id column and an increasing login_date_time column. Neither column allows duplicate values.
How should the listener be configured so it retrieves each row at most one time?

A. Set the watermark column to the login_date_time column
B. Set the target value to the last retrieved login_date_time value
C. Set the target value to the last retrieved user_id value
D. Set the watermark column to the user_id column

Show Suggested Answer

Suggested Answer: A 🗳️

by pgarciar at March 26, 2021, 12:27 p.m.

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pgarciar

Highly Voted 3 years, 9 months ago

A is the correct answer.

upvoted 15 times

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Maxroyo

Highly Voted 2 years, 4 months ago

Selected Answer: A

* Watermark allows the poll scope to poll for new resources instead of getting the same resource over and over again. * The database table must be ordered so that the "watermark functionality" can move effectively in the ordered list. Watermark stores the current/last picked up "record id." * If the Mule application is shut down, it will store the last picked up "record id" in the Java Object Store and the data will continue to exist in the file. This watermark functionality is valuable and enables developers to have increased transparency. * Developers do not need to create code to handle caching; it is all configurable! * There are two columns and both are unique but user_id can't guaranty sequence whereas date_time will always be in increasing order and table content can easily be ordered on the basis of last processed date_time. So correct answer is: Set the watermark column to the date_time column

upvoted 5 times

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VickySoni

Most Recent 9 months, 2 weeks ago

Watermark should be set on Primary key, so D should be the answer.

upvoted 1 times

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ajcacho

1 year, 3 months ago

This is a scenario for watermarking, therefore A has to be the answer, not the pointed B option ('On Table Row' doesn't even have a target parameter as seen in https://docs.mulesoft.com/connectors/db/database-documentation)

upvoted 2 times

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Yug21

1 year, 9 months ago

I am doubtful about option A. Consider a scenario, the user logged in at time A and the row was retrieved by the listener. The same row can be retrieved again if the user logs in later sometime (the logged in column gets updated to the latest time for the same row and possibly greater than watermarking column value), but the question says "each row should be retrieved at most one time". Example: UserId LoginTime 1 10:00 AM At this point of time, watermarking column value = 10:00 AM Later some time same user again logs in then UserId LoginTime 1 12:00 AM This time as the column value is greater than the watermark column value, it will be again retrieved which is against question statement. Is this a valid scenario, can someone please explain? Thanks

upvoted 2 times

notthatgerry

1 year, 2 months ago

I think the statement refers to the fact that every row in login_date_time column is unique as user_id is aswell, so the timestamp for login at 10:00AM and login at 12:AM are two different time stamps taking into consideration that a timestamp has the format yyyymmdd hh:mm:ss.00 in general, so as you can see hardly two users will login at the same time. Also please take into consideration the following: a system as the one described can be used to provide anonymous access to a certain resource, so no matter if the same person access the resource twice, the application generates a unique radomized user_id every time the user access the application. This kind of systems are usefull to generate access tokens so if an unauthorized agent gets an user_id already used, they will not be able to access the resource.

upvoted 1 times

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kampatra

1 year, 11 months ago

Selected Answer: A

A is Correct

upvoted 1 times

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Kbessadi

1 year, 11 months ago

Selected Answer: A

A is the correct answer

upvoted 1 times

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frediepulgoso

2 years, 9 months ago

A is correct

upvoted 1 times

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kubota_dump

2 years, 11 months ago

Selected Answer: B

B is the correct answer.

upvoted 1 times

kubota_dump

2 years, 11 months ago

A. Set the watermark column to the login_date_time column

upvoted 1 times

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senthil_Kumar_Murugan

3 years ago

Selected Answer: A

Set the watermark column to the login_date_time column

upvoted 1 times

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Ella_Z

3 years, 3 months ago

"Neither column allows duplicate values." if there have two user click in same time, them the timestamp may same. So I think the B is correct.

upvoted 2 times

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Anseal

3 years, 7 months ago

I wonder why is D incorrect? I would choose both A and D.

upvoted 2 times

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Rahul_16

3 years, 7 months ago

A is correct. It is done on column not on value

upvoted 3 times

RoyalCasa

3 years, 6 months ago

Because the user_id column can be unique but need not be incremental / higher than the previous user_id. Whereas in case of timestamp, it would always be HIGHER than the previous one. So that would be the ideal watermark column.

upvoted 6 times

ck0241

3 years, 5 months ago

Good explanation, thank you. I wonder what is the importance of ''At most one value' in the question.

upvoted 1 times

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