Metadata fields

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Each document has metadata associated with it, such as the _index and _id metadata fields. The behavior of some of these metadata fields can be customized when a mapping is created.

Identity metadata fields

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_index

The index to which the document belongs.

_id

The document’s ID.

Document source metadata fields

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_source
The original JSON representing the body of the document.
_size
The size of the _source field in bytes, provided by the mapper-size plugin.

Doc count metadata field

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_doc_count
A custom field used for storing doc counts when a document represents pre-aggregated data.

Indexing metadata fields

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_field_names
All fields in the document which contain non-null values.
_ignored
All fields in the document that have been ignored at index time because of ignore_malformed.

Routing metadata field

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_routing
A custom routing value which routes a document to a particular shard.

Other metadata field

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_meta
Application specific metadata.
_tier
The current data tier preference of the index to which the document belongs.