Is Amazon SimpleDB more reliable / affordable than DynamoDB?
This question is not about a general comparison between the two, but more specifically about high availability and reliability. From amazon documentation about this:
Amazon SimpleDB automatically creates multiple geographically dispersed copies of each item of data that you store. This ensures high availability and longevity — in the unlikely event that one replica fails, Amazon SimpleDB can reinstall another replica on the system.
Amazon DynamoDB is a fully managed NoSQL database service that delivers fast, predictable performance with smooth scalability. The service runs through Amazon verified high availability centers. The service replicates data across multiple sites in the AWS Region to provide resiliency in the event of a server failure or an Availability Zone failure.
So, in relative terms, is it more reliable than the other?
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Both services are highly available and reliable. The main difference is performance and cost.
SimpleDB is a NoSQL database as well as DynamoDB, DynamoDB however is designed for one-to-one millisecond of fast performance under any amount of load. SimpleDB will also be fast, but not designed for large datasets.
As a result, billing for DynamoDB is much more expensive. You should also "reserve" use for dynamoDB, not billing you for how many requests you make, billing you for how much you think you are going to do.
DynamoDB - large datasets and high performance
SimpleDB - Small / Medium datasets and cheaper
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