OpenSearch/docs/reference/mapping/fields/source-field.asciidoc

[[mapping-source-field]]
=== `_source` field

The `_source` field contains the original JSON document body that was passed
at index time.  The `_source` field itself is not indexed (and thus is not
searchable), but it is stored so that it can be returned when executing
_fetch_ requests, like <<docs-get,get>> or <<search-search,search>>.

[[disable-source-field]]
==== Disabling the `_source` field

Though very handy to have around, the source field does incur storage overhead
within the index. For this reason, it can be disabled as follows:

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "_source": {
      "enabled": false
    }
  }
}
--------------------------------------------------

[WARNING]
.Think before disabling the `_source` field
==================================================

Users often disable the `_source` field without thinking about the
consequences, and then live to regret it.  If the `_source` field isn't
available then a number of features are not supported:

* The <<docs-update,`update`>>, <<docs-update-by-query,`update_by_query`>>,
and <<docs-reindex,`reindex`>> APIs.

* On the fly <<highlighting,highlighting>>.

* The ability to reindex from one Elasticsearch index to another, either
  to change mappings or analysis, or to upgrade an index to a new major
  version.

* The ability to debug queries or aggregations by viewing the original
  document used at index time.

* Potentially in the future, the ability to repair index corruption
  automatically.
==================================================

TIP: If disk space is a concern, rather increase the
<<index-codec,compression level>> instead of disabling the `_source`.

[[include-exclude]]
==== Including / Excluding fields from `_source`

An expert-only feature is the ability to prune the contents of the `_source`
field after the document has been indexed, but before the `_source` field is
stored.

WARNING: Removing fields from the `_source` has similar downsides to disabling
`_source`, especially the fact that you cannot reindex documents from one
Elasticsearch index to another. Consider using
<<source-filtering,source filtering>> instead.

The `includes`/`excludes` parameters (which also accept wildcards) can be used
as follows:

[source,console]
--------------------------------------------------
PUT logs
{
  "mappings": {
    "_source": {
      "includes": [
        "*.count",
        "meta.*"
      ],
      "excludes": [
        "meta.description",
        "meta.other.*"
      ]
    }
  }
}

PUT logs/_doc/1
{
  "requests": {
    "count": 10,
    "foo": "bar" <1>
  },
  "meta": {
    "name": "Some metric",
    "description": "Some metric description", <1>
    "other": {
      "foo": "one", <1>
      "baz": "two" <1>
    }
  }
}

GET logs/_search
{
  "query": {
    "match": {
      "meta.other.foo": "one" <2>
    }
  }
}
--------------------------------------------------

<1> These fields will be removed from the stored `_source` field.
<2> We can still search on this field, even though it is not in the stored `_source`.