Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictableperformance with seamless scalability. Amazon DynamoDB enables customers to offload theadministrative burdens of operating and scaling distributed databases to AWS, so they don't have toworry about hardware provisioning, setup and configuration, replication, software patching, orcluster scaling.
Today's web-based applications generate and consume massive amounts of data. For example, anonline game might start out with only a few thousand users and a light database workload consistingof 10 writes per second and 50 reads per second. However, if the game becomes successful, it mayrapidly grow to millions of users and generate tens (or even hundreds) of thousands of writes andreads per second. It may also create terabytes or more of data per day.
Developing your applications against Amazon DynamoDB enables you to start small and simply dialupyour request capacity for a table as your requirements scale, without incurring downtime.
You pay highly cost-efficient rates for the request capacity you provision, and let Amazon DynamoDBdo the work over partitioning your data and traffic over sufficient server capacity to meet yourneeds. Amazon DynamoDB does the database management and administration, and you simply storeand request your data. Automatic replication and failover provides built-in fault tolerance, highavailability, and data durability. Amazon DynamoDB gives you the peace of mind that your databaseis fully managed and can grow with your application requirements.
Reference:
http://aws.amazon.com/dynamodb/faqs