The first data store we will look at is LevelDB. It is an open source implementation developed by Google and written in C++. It is supported by a wide range of platforms, including Node.js. LevelDB is a key/value store; both the key and value are represented as binary data, so their content can vary from simple strings to binary representations of serialized objects in any format, such as JSON or XML. As it is a key/value data store, working with it is similar to working with an associative array—a key identifies an object uniquely within the store. Furthermore, the keys are stored as sorted for better performance. But what makes LevelDB perform better than an arbitrary file storage implementation?

Well, it uses a "log-structured merge" topology, which stores all write operations in an in-memory log, transferred (flushed) regularly to a permanent storage called Sorted String Table (SST) files. Read operations first attempt to retrieve entries from a cache containing...