Elasticsearch, get average document length

Question

Is there any better way in elasticsearch (other than issuing a match all query and manually averaging over the length of all returned documents) to get the average document

Answer 1

In ElasticSearch 6.2 you should just use the following line (no need to add 'terms'):

  "aggs" : 
      {"avg_size" : 
           {"avg" : 
               {"field" : "_size"}}}

See details here: https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-metrics-avg-aggregation.html