ElasticSearch Query for each extension get the sum of its length

I'm looking to find the sum of each extension. The json file contains

Sample code

       {"index":{"_id":"202"}} 
        "length":500000
         "extension":".jpeg"

Output wanted

Key: Jpeg 10000000 Key: docx 20000000

Tried code

        GET /crud_sample2/Customer_Info/_search?extension
          { 
          "aggs": {
          "sum": {
            "terms": {
              "field": "length"
              }
          }
           }
        } 

Output

"key": 500000, "doc_count": 15

Try this instead

GET /crud_sample2/Customer_Info/_search
{
  "aggs": {
    "sum": {
      "terms": {
        "field": "extension",
        "order": {"total_length": "desc"}
      },
      "aggs": {
        "total_length": {
          "sum": {
            "field": "length"
          }
        }
      }
    }
  }
}