Membase can someone explain the idea behind their technology

It is fourth day already since I've started diving into CouchDB specifically Membase (Couchbase), Membase seems really interesting technology for me due to simplicity of administration, their interface is as magical as informal and simple. The way you add/remove buckets is just fun.

Unfortunately I didn't managed to launch their .NET client on Mac OS X (on Windows it worked fine) and also couldn't find out the way to perform Map/Reduce queries so it seemed that Membase Server technology is little simpler then pure CouchDB. Anyway everything changed until recently I've stumbled upon the diagram that describes their technology:

The Image is explained here

It seems that "Couchbase server (Currently Membase Server)" plays role of some sort of Master database which isn't accessed directly, and also there is "Couchbase Single Server" which plays the role of client database which has all the features of CouchDB (such as Map/Reduce queries)

If so then how is "CouchSync" is performed? Is it possible to perform this "CouchSync" from code?

Before I describe to you how CouchSync works I think it would be beneficial for me to describe how the Couchbase product history evolved. This will make things more clear. About a year ago, Membase Server was first released. The idea behind Membase Server was to provide memcached with persistence (the persistence layer was sqlite) and simple to use clustering technology. Then about 6 months ago the companies Membase and CouchOne merged to form Couchbase. Directly after the merger Couchbase continued to provide Membase Server, but now also provided Couchbase Single Server. Couchbase Single Server is essentially CouchDB with GeoCouch packaged in by default along with many major performance improvements. On July 29th, 2011 Couchbase announced a developer preview of the first version of Couchbase Server. Couchbase Server is the combination of Couchbase Single Server and Membase. Basically what Couchbase did was replace sqlite with CouchDB as the persistence engine. So this basically caused the product to go from being a key-value store to a document store database.

So what is CouchSync?

CouchSync is basically what Couchbase is calling CouchDB replication. It is very simple to setup in both Couchbase Server, Couchbase Single Server and in CouchDB. All it is is a changes feed that is streamed from one server to another.

A note on using Membase. Since Membase doesn't provide any of the CouchDB support it doesn't actually fit into this diagram and therfore doesn't support CouchSync. You will actually want to look at the developer preview of Couchbase Server since this product has both Membase and CouchDB features. In the meantime if you are looking for something more stable to test then take a look at Couchbase Single Server as it will be able to give you a feel for some of the features (like CouchSync) that are in Couchbase Server

Also, the point of this diagram is to show that you can do CouchSync across the entire Couchbase product line. You don't need to go through Couchbase Single Server to do CouchSync to Couchbase Mobile. You can do CouchSync directly from Couchbase Server.

Is it possible to perform CouchSync from code? No. It's easier than that. You set it up in the web ui.

Hope that helps.

[EDIT]: This diagram is now outdated. Couchbase the company no longer supports Couchbase Single Server (which is it's version of CouchDB). The CouchSync feature will now sync directly with Couchbase server.