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AWS Certified Developer - Associate > DynamoDB > Flashcards

DynamoDB Flashcards

1
Q

You can select a specific Availability Zone in which to place your DynamoDB Table.

A

False.

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2
Q

How can you optimise the performance of a large scan in DynamoDb?

A

Run smaller scans in parallel.

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3
Q

What is some characteristics of DynamoDB?

A
  • NoSQL database that supports both key-value and document data models
  • It is a fast, millisecond latency at any scale
  • Flexible data model
  • Reliable performance
  • Serverless
  • Can be configured to auto scale
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4
Q

Name a few applications for which DynamoDB is a good choice.

A
  • Mobile apps
  • Web
  • Gaming
  • Ad-tech
  • IoT
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5
Q

How is the data stored in DynamoDB?

A
  • Stored on SSD storage

- Spread across 3 geographically distinct data centers

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6
Q

What can documents in DynamoDB be written in?

A
  • JSON
  • HTML
  • XML
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7
Q

What is used for authentication and access control to a DynamoDB?

A

IAM

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8
Q

How can you make sure that an user only can access their own data in DynamoDB?

A
  • By adding a Condition to an IAM Policy that checks so that the Partition Key value matches the User ID.
  • “dynamodb:LeadingKeys”
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9
Q

DynamoDB supports both Eventually Consistent and Strongly Consistent reads, which it the default?

A

Eventual Consistency.

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10
Q

In DynamoDB, how can you specify what attributes a query or scan should return?

A

By specifying the ProjectionExpression parameter.

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11
Q

You’re doing a query on a DynamoDB table, how is the result sorted? Can you change this in any way?

A
  • The result is sorted by the Sort Key
  • Numeric order - by default in ascending order (1, 2, 3)
  • ASCII character code values
  • You can revers the order by setting the ScanIndexForward parameter to false
  • Only for queries, not scans
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12
Q

By default, are queries eventual or strongly consistent?

A

Eventual. If you want Strong Consistency you need to specify it

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13
Q

How can you refine the result of a scan?

A
  • Filter the result.
  • Remember that the scan still fetches ALL the data of the table, filter simply filters out what to show you after all data has been fetched
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14
Q

How can you improve the performance of a query or scan?

A
  • Set a smaller page size, this will use fewer read operations
  • Try to design the tables in a way so that you can use Query, Get or BatchGetItem instead of Scan
  • Parallel scans (not recommended if your table/index is quite busy)
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15
Q

Which are the two pricing models for DynamoDB?

A
  • Provisioned Throughput

- On-Demand Capacity

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16
Q

How does the On-Demand Capacity model work for DynamoDB?

A
  • You don’t need to specify your requirements
  • DynamoDB instantly scales up and down based on the activity of your application
  • Great for unpredictable workloads, if you workload has large short lived spikes, if you do not know your capacity requirements, or if it is a new application where the workload isn’t well understood
  • You only pay for what you use (read, write, storing data)
17
Q

When should you use the Provisioned Throughput model for DynamoDB?

A
  • When you can forecast read and write capacity requirements
  • Predictable application traffic
  • Application traffic is consistent or increases gradually
18
Q

You can change you DynamoDB table from Provisioned to On-Demand once per day.

A

True.

19
Q

What does DAX stand for, and what is it?

A
  • DynamoDB Accelerator
  • It’s a fully managed, clustered in-memory cache for DynamoDB
  • Only for Read
  • Good for Read-Heavy and bursty workloads
  • My be able to reduce the Provisioned Read Capacity on your DynamoDB table (can save money)
20
Q

Give a few examples of when to use DAX.

A
  • Auction applications
  • Gaming
  • Retail sites during Black Friday/Christmas promotions
21
Q

How does DAX work?

A
  • It’s a write-through caching service
  • Data is written to the cache as well as the back end store at the same time
  • Allows you to point your DynamoDB API calls at the DAX cluster
  • If the item you are querying is in the cache (cache hit), DAX returns the result to the application
  • If the item is not found in DAX (cache miss) then DAX performs an Eventually Consistent GetItem operation against DynamoDB
  • The item is the written to the cache, as well as returned to the one asking for it
22
Q

When is DAX not a good choice?

A
  • If the application requires Strongly Consistent reads
  • DAX works with Eventually Consistent reads only
  • Write intensive applications
  • Applications that do not perform many read operations
  • Applications that do not require microsecond response time
  • If you need a Lazy Loading strategy
  • DAX only supports write-through
23
Q

What is DynamoDB Transactions?

A
  • Supports and all or nothing approach to the database transactions
  • Good for mission-critical applications
  • ACID Transactions (Atomic, Consistent, Isolated, Durable)
24
Q

What is DynamoDB TTL?

A
  • Allows you to set an expiry time for your data
  • Expired items are automatically marked for deletion
  • The item will be deleted within the next 48 hours
  • Great for removing irrelevant or old data such as:
  • Session data
  • Event logs
  • Temporary data
  • Reduces cost by automatically removing data which is no longer relevant
  • You can filter out expired items from your queries and scans
  • You choose which attribute you will base the TTL on
25
Q

What is DynamoDB Streams?

A
  • Time-ordered sequence of item level modifications (insert, update, delete)
  • Logs are encrypted at rest
  • Logs are stored for 24 hours
  • By default the Primary Key is recorded
  • Before and After images of the item can be captured
  • DynamoDB Streams can be used for auditing or achieving of transactions, replaying transactions to another table, trigger events based on a particular change within the DynamoDB table (e.g. can trigger Lambda, Lambda polls the DynamoDB Stream)
  • The Stream has its own endpoint
26
Q

In DynamoDB, what does the ProvisionedThroughputExceededException mean? How can we solve this?

A
  • You request rate is too high for the read/write capacity provisioned on you DynamoDB table?
  • The SDK will automatically retry the request until it is successful
  • All AWS SDKs use Exponential Backoff
  • If you’re not using the SDK:
  • Reduce request frequency
  • Use Exponential Backoff
  • If the requests keep failing after about one minute, your request size may be exceeding the throughput for your read/write capacity
  • If the workload mainly is get requests you might be able to improve the performance using DAX or ElastiCache
  • If it is mainly write requests you might have to increase your write capacity for the table

AWS Certified Developer - Associate (18 decks)

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