[ES 공식문서] _source field

관련: .mapping 파일
참고: https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-source-field.html

The _source field contains
the original JSON document body
that was passed at index time.

The _source field is not indexed (is not searchable),
it can be returned when executing fetch requests, like get or search.

If disk usage is important
방법1. synthetic _source 

• shrinks disk usage
• slower fetches

방법2. disabling the _source field

• (not recommended)  
• shrinks disk usage
• disables many features.

일반적인 경우 이렇게 사용하는 것 같다

"_source": {
  "enabled": true
},