Dynamo DB

Question 1

An application doing Strongly Consistent reads of 10 items per second, with each item 10 KB in size. What RCU do you choose?

Answer 1

30

Question 2

An application doing Eventually Consistent reads of 12 items per second, with each item 16 KB in size. What RCU do you choose?

Answer 2

We can do 2 Eventually Consistent reads per seconds for items of 4 KB with 1 RCU. 12 * (16 KB / 4 KB) = 48 / 2 = 24 RCU.

Question 3

You are working on designing a new DynamoDB table where you want to make a Query using an attribute that’s NOT part of your table’s Primary Key. You need to use the >= predicate while keeping the same Partition Key. What should you do to make this query efficient?

Answer 3

Local secondary index

Question 4

Which feature of DynamoDB allows you to achieve Optimistic Locking?

Answer 4

conditional writes

Question 5

You would like to paginate the results of a DynamoDB Scan operation in order to minimize the number of items returned in the CLI’s output. Which of the following AWS CLI options should you use?

Answer 5

-max-items &-starting-token

Question 6

You have an e-commerce website where you are using DynamoDB as your database. You are about to enter the Christmas sale and you have a few items which are very popular and you expect that they will be read often. Unfortunately, last year due to the huge traffic you had the ProvisionedThroughputExceededException exception. What would you do to prevent this error from happening again?

Answer 6

create dax cluster

Question 7

You are running an application in production that is leveraging DynamoDB as its datastore and is experiencing smooth sustained usage. There is a need to make the application run in development mode as well, where it will experience an unpredictable volume of requests. What is the most cost-effective solution that you recommend?

Answer 7

use provisioned capacity mode with auto scaling for production and on demand capacity for development

Question 8

DynamoDB tables scale ……………………..

Answer 8

horizontaly

Question 9

An application doing Strongly Consistent reads of 10 items per second, with each item 10 KB in size. What RCU do you choose?

Answer 9

10 KB gets rounded to 12 KB. 10 * (12 KB / 4 KB) = 30 RCU.

Question 10

wHAT RECORDS CAN BE IN DYNAMODB STREAMS

Answer 10

Stream records can be:
* Sent to Kinesis Data Streams
* Read by AWS Lambda
* Read by Kinesis Client Library applications

Question 11

data retention time in db streams

Answer 11

24h

Question 12

dynamod db dax vs elasticache

Answer 12

Question 13

dynamodb scan characteristic

Answer 13

Returns up to 1 MB of data – use pagination to keep on reading
Consumes a lot of RCU
Can use ProjectionExpression & FilterExpression

Question 14

how to improve scan

Answer 14

use Parallel Scan

Question 15

Partition Key + Sort Key (HASH + RANGE) characteristic

Answer 15

• The combination must be unique for each item
• Data is grouped by partition key

Question 16

dynamodb provisioned mode characterisitic

Answer 16

• Provisioned Mode (default)
• You specify the number of reads/writes per second
• You need to plan capacity beforehand
• Pay for provisioned read & write capacity units

Question 17

dynamodb on demand mode characterisitc

Answer 17

• On-Demand Mode
• Read/writes automatically scale up/down with your workloads
• No capacity planning needed
• Pay for what you use, more expensive ($$$)

Question 18

If Burst Capacity has been consumed, you’ll get a …, and how to take care of it ?

Answer 18

“ProvisionedThroughputExceededException”
use exponential backoff retry

Question 19

how many RCU 10 Strongly Consistent Reads per second, with item size 6 KB

Answer 19

We need 10 ∗(8/4)= 20 Rcu(we must round up 6 KB to 8 KB)

Question 20

how are spreated wcu and rcu actoss partition

Answer 20

evenly

Question 21

“ProvisionedThroughputExceededException” reasons and solutions

Answer 21

• Hot Keys – one partition key is being read too many times (e.g., popular item)
• Hot Partitions
• Very large items, remember RCU and WCU depends on size of items
• Solutions:
• Exponential backoff when exception is encountered (already in SDK)
• Distribute partition keys as much as possible
• If RCU issue, we can use DynamoDB Accelerator

Question 22

max returon size for query

Answer 22

1MB

Question 23

how to retreive to retrieve only certain attributes with getItem

Answer 23

use ProjectionExpression

Question 24

dynamodb BatchWriteItem limits

Answer 24

• Up to 25 PutItem and/or DeleteItem in one call
• Up to 16 MB of data written, up to 400 KB of data per item
• Can’t update items (use UpdateItem)
• UnprocessedItems for failed write operations

Question 25

BatchGetItem dybamodb limits

Answer 25

Return items from one or more tables
* Up to 100 items, up to 16 MB of data
* Items are retrieved in parallel to minimize latency
* UnprocessedKeys for failed read operations (exponential backoff or add RCU)

Question 26

what allow to use SQL in dynamodb ?

Answer 26

PartiQL
* SQL
-compatible query language for DynamoDB

Question 27

conditional expresions dynamodb

Answer 27

attribute_exists
* attribute_not_exists
* attribute_type
* contains (for string)
* begins_with (for string)
* ProductCategory IN (:cat1, :cat2) and Price between :low and :high
* size (string length)

Question 28

difference Filter Expression vs Condition Expression

Answer 28

Filter Expression filters the results of read queries, while Condition Expressions are for write operations