What's the point of using Amazon SimpleDB?

Question

I thought that I could use SimpleDB to take care of the most challenging area of my application (as far as scaling goes) - twitter-like comments, but with location on top - till

Answer 1

I use SDB on a couple of large-ish applications. The 10 GB limit per domain does worry me, but we are gambling on Amazon allowing this to be extended if we need it. They have a request form on their site if you want more space.

As far as cross domain joins, don't think of SDB as a traditional database. During the migration of my data to SDB, I had to denormalize some of it so I could manually do the cross domain joins.

The 1000 byte per attribute limitation was tough to work around also. One of the applications I have is a blog service which stores posts and comments in the database. While porting it over to SDB, I ran into this limitation. I ended up storing the posts and comments as files in S3, and read that in my code. Since this server is on EC2, the traffic to S3 isn't costing anything extra.

Perhaps one of the other problems to watch out for is the eventual consistency model on SDB. You can't write data and then read it back with any guarantee that the newly written data will be returned to you. Eventually the data will be updated.

All of this said, I still love SDB. I don't regret switching to it. I moved from a SQL 2005 server. I think I had a lot more control with SQL, but once giving up that control, I have more flexibility. Not needing to pre-define the schema is awesome. With a strong and robust caching layer in your code, it's easy to make SDB more flexible.