Amazon SimpleDB

[2] As with EC2 and S3, Amazon charges fees for SimpleDB storage, transfer, and throughput over the Internet.

On December 1, 2008, Amazon introduced new pricing with Free Tier[3] for 1 GB of data & 25 machine hours.

By foregoing consistency, the system is able to achieve two other highly desirable properties: Component failures are assumed to be inevitable; thus, both of these properties were deemed necessary in order to provide a reliable web service.

They address a problem that arises when accessing SimpleDB concurrently.

Consider a simple program that uses SimpleDB to store a counter, i.e. a number that can be incremented.

This introduces some additional complexity; if SimpleDB was not able to store the new value because the current value was not as expected, the program must repeat steps 1–3 until the conditional put operation actually changes the stored value.

There has been some talk of SimpleDB being superseded by DynamoDB (it is no longer being "iterated on",[6] though Amazon does not plan to remove it).