Questions[nosql](server)

Is it possible to scale out a RDB ? If it's possible, how can one achieve it?

I'm asking this question because I assisted to a NoSQL event in which the speaker told many times that the one of the disadvantages of relational databases is the impossibility to scale out. In other word, we should add more ram and more storage but we can't just add another computer like we would do if we're using a NoSQL database.

Background: I'm writing a web application that will be available to the world at large on a software-as-a-service basis. As input to my choosing a database platform, I've been reading up on 'NoSQL' databases like Cassandra, Riak, MongoDB, and Redis. Replication, sharding, and partitioning are prominent in the feature sets of all of these databases.

I'll end up choosing one of them and getting on with development, but what troubles me is whether I'll realistically be able to take advantage of all of that database sharding/distribution goodness in production.

I'm a one-man start-up with a production technology infrastructure consisting of one SliceHost slice running Centos. I don't ever expect to run my own server hardware. I just want to have a view now of the kind of server architecture I could move towards when my product becomes overwhelmingly successful. :-)

How do people set up clusters of servers to support their nifty NoSQL database distribution schemes in a VPS environment? In most (all?) cases, the database products expect to run on a private LAN, and therefore lack the authentication mechanisms you'd need to support clusters spanning the wild woolly Internet world. How does one establish a private LAN in 'the cloud'? Do VPS providers offer that kind of thing? SliceHost seems to offer private IP addresses, but those addresses are accessible by all of their customers; they are not restricted to one particular customer.

I am wondering where to begin with database scaling/optimization strategies. After reading articles like highscalability.com's facebook architecture article, and this twitter architecture article, I am not sure if by RAM they mean only memcached, or something else.

My questions are:

• Can entire SQL databases be stored in RAM? I'm thinking sharding and all that here... Just learning (not from a db background).
• Are SQL database indexes stored in RAM?
• Are NOSQL databases stored in RAM? Can they be?
• Or is Memcached the standard for storing things in RAM? So 99% of requests read from RAM (Memcached), and the database (disk) is a backup?

Just looking for a point in the right direction.

I am wondering where to begin with database scaling/optimization strategies. After reading articles like highscalability.com's facebook architecture article, and this twitter architecture article, I am not sure if by RAM they mean only memcached, or something else.

My questions are:

• Can entire SQL databases be stored in RAM? I'm thinking sharding and all that here... Just learning (not from a db background).
• Are SQL database indexes stored in RAM?
• Are NOSQL databases stored in RAM? Can they be?
• Or is Memcached the standard for storing things in RAM? So 99% of requests read from RAM (Memcached), and the database (disk) is a backup?

Just looking for a point in the right direction.

For an application we want to achieve zero database and application down time using Active Active configuration. Our dB is Oracle

Following are my questions:

1. How can we achieve active active configuration in Oracle?
2. Will introducing Cassandra/HBase(or any other No SQL dbs) cloud help in zero downtime or it is only for fast retrieval of data in a large db?
3. Any other options?

Thanks and Regards, Hiral