What exactly is NoSQL?

Question

What exactly is NoSQL? Is it database systems that only work with {key:value} pairs?

As far as I know MemCache is one of such database systems, am I right?

What other popular NoSQL databases are there and where exactly are they useful?

Thanks, Boda Cydo.

Answer 1

I used something called the Raima Data Manager more than a dozen years ago, that qualifies as NoSQL. It calls itself a "Set Oriented Database" Its not based on tables, and there is no query "language", just an C API for asking for subsets.

It's fast and easier to work with in C/C++ and SQL, there's no building up strings to pass to a query interpreter and the data comes back as an enumerable object rather than as an array. variable sized records are normal and don't waste space. I never saw the source code, but there were some hints at the interface that internally, the code used pointers a lot.

I'm not sure that the product I used is even sold anymore, but the company is still around.

Answer 2

To quickly get a handle on NoSQL systems, see this blog post I wrote: Visual Guide to NoSQL Systems. Essentially, NoSQL systems sacrifice either consistency or availability in favor of tolerance to network partitions.