AWS > Database > Amazon DynamoDB:
Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability.
It is a fully managed database and supports both documentand key-value data models
It a great fir for mobile, web, gaming, ad-tech, IoT.
Noted:
1. All of your data is stored on solid-state disks (SSDs)
2. It is automatically replicated across multiple Availability Zones in an AWS Region.
3. You can use global tables to keep DynamoDB tables in sync across AWS Regions
4. Eventual Consistent Read (Default)
5. Strongly Consistent Read
Eventual Consistent Read:
Consistency across all copies of data is usually reached within a second. Repeating a read after a short time should return the updated data. (Best read performance)
最終一致性: 保證當一個 update/insert 發生後，所有的 read request 會最終 (eventual) 讀取到操作發生後的值。換句話說，假設一條node A 中一條記錄x = 10, 下一個update request set x = 20. 如果使用Eventual Consistency 的架構，那麼之後發生的read request 仍有可能拿到x = 10. 只不過最終在未來某個時間點，所有read request 都會拿到x = 20. 但這個時間點是不能保證的。
Strongly Consistent Read:
A strongly consistent read returns a result that reflects all writes that received a successful response prior to the read.
強制一致性: 傳統的關係型數據庫是天然的強制一致性。當一條數據發生添加、更新操作時，強制一致性保證，在操作完成之後，所有之後查詢該條記錄的請求都會拿到最新的數據。
Reference:
1. AWS Documentation - What Is Amazon DynamoDB?:
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Introduction.html
2. Udemy - AWS Solutions Architect - Associate:
https://www.udemy.com/aws-certified-solutions-architect-associate/
最初發表 / 最後更新: 2020.01.13 / 2020.06.09
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