_source field

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`_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 get or search.

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:

PUT tweets
{
  "mappings": {
    "_source": {
      "enabled": false
    }
  }
}

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 update, update_by_query, and reindex APIs.
On the fly 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.

If disk space is a concern, rather increase the compression level instead of disabling the _source.

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.

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 instead.

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

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

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

GET logs/_search
{
  "query": {
    "match": {
      "meta.other.foo": "one" 
    }
  }
}