Question 1

Puzzle 1:

Which of these can explain why WCU (Write Cost Unit) is double the request amount?

Accepted Answer

All of the above

Answer

The average table items are over 1kb in size.

Answer

There is a capacity uptake from the LSI equal to the original write cost.

Answer

WCU are consumed writing to other regions.

Answer

There is a Global Secondary Index which is the same size as the base table.

Question 2

Puzzle 2:
I have global tables and the write rates don’t match across regions. Why?

Accepted Answer

a) and c)

Answer

b) and c)

Answer

c) TTL deletion

Answer

All of the above

Answer

a) Failed conditional writes

Answer

b) Writing different things to different regions

Answer

a) and b)

Question 3

Puzzle 3
What are the trade offs to having a GSI the same size as the main table?

Accepted Answer

Double Storage Cost and WCU

Answer

Double WCU Cost

Answer

Double DDB CDC Stream Cost and Storage Cost

Answer

Double Storage Cost

Answer

Double DDB CDC Stream Cost and RCU

Answer

Double DDB CDC Stream Cost

Answer

None of the above

Answer

Double RCU Cost

Answer

Double DDB CDC Stream Cost and WCU

Answer

All of the above

Question 4

Puzzle 4

How can I sample 1,000 random items from my table?

Accepted Answer

Use DynamoDBMapper.parallelScan() with multiple threads

Answer

Run a table scan and stop once 1,000 items have been returned

Answer

Call BatchGetItem 10 times

Question 5

Puzzle 5: How can I fetch a list of unique partition keys from my table?

Accepted Answer

Scan the whole table and deduplicate

Answer

Use the GetAllPartitionKeys method from the DDB client

Answer

All of the above

Question 6

Puzzle 6

How can we bulk update/delete a significant number of items in my table easily?

Accepted Answer

Implement a parallel scan with N segments, process segments randomly, and repeat

Answer

A simple table scan should suffice given we're updating the majority of items

Answer

Create a new GSI with only the PK/SK and fields to be updated, then update the GSI items

Question 7

Puzzle 7: X would like assistance in ways to estimate and reduce the cost when modifying a single attribute on ~550 billion items

Accepted Answer

Purchase reserved capacity

Answer

Use UpdateItem instead of PutItem calls

Answer

All of the above

Question 8

Puzzle 8
I configured 30,000 WCUs but I see lots of throttles.
CloudWatch shows I'm consuming just 2,500 WCUs. Why?

Accepted Answer

Cloud Watch granularity.

Answer

Large GSIs.

Answer

A couple (less than 8) Global Tables using up WCU at the same time.

Answer

A lot of writes that weren't confirmed and retried as a result.

Question 9

Puzzle 9

What's the best way to recover data on a large table at a certain point in time?

Accepted Answer

Use PITR with incremental exports to find the deltas, and process them manually

Answer

Use PITR to restore a snapshot as at a point in time

Answer

Use ERS recovery to restore a snapshot to a backup table, filter data, then manually insert

Related quizzes

Related quizzes