1、对elsasticsearch index的解释，What exactly is an index in Elasticsearch ?
basic definition
An index is defined as:
An index is like a ‘database’ in a relational database. It has a mapping which defines multiple types.
An index is a logical namespace which maps to one or more primary shards and can have zero or more replica shards.
Ok. So there are two concepts in that definition. First, an index is some type of data organization mechanism, allowing the user to partition data a certain way. The second concept relates to replicas and shards, the mechanism Elasticsearch uses to distribute data around the cluster.
Let’s explore the first concept, using indices to organize data.
文章详细内容见此博文：http://www.elasticsearch.org/blog/what-is-an-elasticsearch-index/