Now you are able to create a bucket and store documents in it. So, let's try to understand another concept, vBucket, which helps in replicating documents across the nodes in a cluster, before moving to the next chapter. In order to understand vBucket, you need to understand document ID, which we already discussed. It is a unique key per bucket, that is associated with each document. Whenever an application needs to store a document in a bucket, it needs to be associated with a unique key, just as a primary key does in the RDBMS table.

Depending on the document ID, documents are distributed across the nodes in a cluster. Each bucket is divided into 1024 logical partitions which are called vBucket. Each partition is bound to a particular node in the cluster. This bindings of vBucket to server nodes is stored in a cluster map, which is a lookup structure. Each vBucket will have a subset of document IDs. This mechanism allows effective distribution and sharding of documents across the...