Amazon has added a database to its collection of "cloud computing" tools for developers. SimpleDB as the new service is known, offers developers a database on pay-as-use basis, which, as Dave Winer points out, is good news for those with scalability concerns.
As with S3, the price structure is relatively simple and affordable. In terms of bandwidth, SimpleDB will set you back $0.14 per Amazon SimpleDB Machine Hour consumed, $0.10 per GB transfer in and $0.18 per GB transfer out. The data storage itself will run $1.50 per GB a month.
The scalability that Winer touts means if your site languishes in obscurity you need only pay for whatever little space you use, but if your site becomes a sudden success and database demands spike, Amazon handles the load without the need to invest in costly new database servers and replication.
Another advantage SimpleDB has over other options is that it's universally accessible. Many host providers offer databases that are only accessible online, which means to offer an API and allow users to build desktop tools you'll need to invest in a more robust system.
Also, unlike a relational database such as PostgresQL or MySQL, Amazon's SimpleDB doesn't have a schema, which makes it somewhat more flexible and puts it in league with the alpha database project CouchDB.
However, SimpleDB may not be as much of a panacea as Winer sees it given some of its limitations. It is called SimpleDB after all.
Perhaps the biggest concern for developers wanting to use SimpleDB is the lack of consistency. Instead SimpleDB has what it calls “Eventual Consistency:”
In short, what happens if you sell the last widget in stock at your online store and it takes a second for that data to propagate, during which time you sell the last widget again? A lack of consistency won't matter to every web app, but it might make retailers think twice.
Still, if you're looking for a cheap, flexible way to store some of your data without having to invest in a custom database setup SimpleDB might do the trick.
