When we ingest a document into index, Elasticsearch adds a few meta fields to each index document. The following is the list of meta fields with reference to our sample my_index:
- _index: Name of the index. my_index.
- _type: Mapping type. "customer" (deprecated in version 6.0).
- _uid: _type + _id (deprecated in version 6.0).
- _id: document_id (1).
- _all: This concatenates all the fields of an index into a searchable string (deprecated in version 6.0).
- _ttl: Life a document before it can be automatically deleted.
- _timestamp: Provides a timestamp for a document.
- _source: This is an actual document, which is automatically indexed by default.
