_sourceedit

The _source field is an automatically generated field that stores the actual JSON that was used as the indexed document. It is not indexed (searchable), just stored. When executing "fetch" requests, like get or search, the _source field is returned by default.

Disabling sourceedit

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": {},
  "tweet": {
    "_source": {
      "enabled": false
    }
  }
}
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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 update API.
  • 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.

Including / Excluding fields from sourceedit

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

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

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

GET logs/event/_search
{
  "query": {
    "match": {
      "meta.other.foo": "one" 
    }
  }
}
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These fields will be removed from the stored _source field.

We can still search on this field, even though it is not in the stored _source.

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 or a transform script instead.

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