On-demand capacity mode: DynamoDB charges you for the data reads and writes your
application performs on your tables. You do not need to specify how much read and write
throughput you expect your application to perform because DynamoDB instantly accommodates your
workloads as they ramp up or down.
Provisioned capacity mode: you specify the number of reads and writes per second
that you expect your application to require. You can use auto scaling to automatically adjust
your table’s capacity based on the specified utilization rate to ensure application performance
while reducing cost.
Reserved pricing is available for provisioned mode but is not actually a "read/write mode". There
is no Spot pricing option for DynamoDB.