Extending your index structure with additional internal information

Apart from the fields that are used to hold data, we can store additional information along with the documents. We already talked about different mapping options and what data type we can use. We would like to discuss in more detail some functionalities of Elasticsearch that are not used every day, but can make your life easier when it comes to data handling.

Note

Each of the field types discussed in the following sections should be defined on an appropriate type level—they are not index wide

Identifier fields

As you may recall, each document indexed in Elasticsearch has its own identifier and type. In Elasticsearch, there are two types of internal identifiers for the documents.

The first one is the _uid field, which is the unique identifier of the document in the index and is composed of the document's identifier and document type. This basically means that documents of different types that are indexed into the same index can...