One of the newest features of the spymemcached client library is called vbucket support. The vBucket algorithm allows Membase to automatically connect clients to the data they need even if servers are being rearranged, taken offline, and so on. It is an indirection layer on top of buckets in Membase that are transparent to clients. According to an article written by Dustin Sallings the basic requirements that led to the development of vbuckets are as follows:

If you want to know more about vbuckets, be sure to read Dustin's article.

You have been using a pre-release version of the spymemcached client library to complete the rest of this tutorial, and inside it a new NodeLocator implementation exists that uses vbucket hashing. It is designed to automatically adjust to the changing topology of your Membase cluster at runtime.

All you need to start using this functionality is to use a new MemcachedClient constructor that allows you to pass in a list of base URIs, and the bucket name and password. Replace the first three lines of the connect() method you wrote earlier with the following lines:

URI base = new URI(String.format("http://%s:8091/pools", serverAddress);
List<URI> baseURIs = new List<URI>();
baseURIs.add(base);
client = new MemcachedClient(baseURIs, "private",
"private", "private");

Compile and run the application:

$ mvn assembly:assembly
$ java -jar target\membasetutorial-exe.jar serverhost

Replace serverhost with the name or IP address of your server, you won't need the port this time. You will see something like the following output:

INFO: Connection state changed for sun.nio.ch.SelectionKeyImpl@16930e2
Connection established with acme-ubuntu-11/10.0.0.57:11210
Reconnected count: 1
19-May-2011 10:09:25 PM net.spy.memcached.auth.AuthThread$1 receivedStatus
INFO: Authenticated to acme-win7/10.0.0.33:11210
You are user 7.
19-May-2011 10:09:25 PM net.spy.memcached.auth.AuthThread$1 receivedStatus
INFO: Authenticated to acme-ubuntu-11/10.0.0.57:11210
Registration succeeded.
There are currently 4 connected.
Enter text, or /who to see user list, or /quit to exit.

You can see that it connects to the server and automatically loads the list of all Membase servers, connects to them and authenticates. It uses the vbucket algorithm automatically, and no code changes to the application will be required.