KindleYou is a location-based social search mobile app that allows users to like or dislike other users, and allows users to chat if both parties liked each other in the app. It has more than 1 billion customers across the world.
They use DynamoDB to support the mobile application and S3 to host the images and other documents shared between users.
The application tracks # of photos uploaded for a specific user real-time. Which of the following option would help us to retrieve the top most friendly user in efficient manner?

Answer options:

A.Using Sparse Indexes
B.Using Aggregation
C.Using Global Secondary Index Overloading
D.Using Global Secondary Index Sharding

Answer: A
Option A is correct -Add a Boolean attribute ‘Is_Top_Friendly’ to the table and add a sparse index. Sparse indexes are useful for queries over a small subsection of a table.
Option B is incorrect -Aggregation of data for maintaining near real-time aggregations and key metrics on top of rapidly changing data is becoming increasingly valuable to businesses for making rapid decisions
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-gsi-aggregation.html
Option C is incorrect -Overloading GSI only addresses adding different fields as to cater different queries
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-gsi-overloading.html
Option D is incorrect -To enable selective queries across the entire key space, you can use write sharding by adding an attribute containing a (0-N) value to every item that you will use for the global secondary index partition key
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-indexes-gsi-sharding.html