elasticsearch/docs/reference/elasticsearch-plugins/mapper-size-usage.md

mapped_pages
https://www.elastic.co/guide/en/elasticsearch/plugins/current/mapper-size-usage.html

Using the _size field [mapper-size-usage]

In order to enable the _size field, set the mapping as follows:

PUT my-index-000001
{
  "mappings": {
    "_size": {
      "enabled": true
    }
  }
}

The value of the _size field is accessible in queries, aggregations, scripts, and when sorting. It can be retrieved using the fields parameter:

# Example documents
PUT my-index-000001/_doc/1
{
  "text": "This is a document"
}

PUT my-index-000001/_doc/2
{
  "text": "This is another document"
}

GET my-index-000001/_search
{
  "query": {
    "range": {
      "_size": {                      <1>
        "gt": 10
      }
    }
  },
  "aggs": {
    "sizes": {
      "terms": {
        "field": "_size",             <2>
        "size": 10
      }
    }
  },
  "sort": [
    {
      "_size": {                      <3>
        "order": "desc"
      }
    }
  ],
  "fields": ["_size"],                <4>
  "script_fields": {
    "size": {
      "script": "doc['_size']"        <5>
    }
  }
}

1. Querying on the _size field
2. Aggregating on the _size field
3. Sorting on the _size field
4. Use the fields parameter to return the _size in the search response.
5. Uses a script field to return the _size field in the search response.

::::{admonition} Using _size in {{kib}} :class: note

To use the _size field in {{kib}}, update the metaFields setting and add _size to the list of meta fields. metaFields can be configured in {{kib}} from the Advanced Settings page in Management.

::::