Elasticsearch Top 10 Most Frequent Values In Array Across All Records

Question

I have an index "test". Document structure is as shown below. Each document has an array of "tags". I am not able to figure out how to query this index to get top 10 most frequently occurring tags?

Also, what are the best practices one should follow if we have more than 2mil docs in this index?

{
    "_index" : "test",
    "_type" : "data",
    "_id" : "1412879673545024927_1373991666",
    "_score" : 1.0,
    "_source" : {
      "instagramuserid" : "1373991666",
      "likes_count" : 163,
      "@timestamp" : "2017-06-08T08:52:41.803Z",
      "post" : {
        "created_time" : "1482648403",
        "comments" : {
          "count" : 9
        },
        "user_has_liked" : true,
        "link" : "https://www.instagram.com/p/BObjpPMBWWf/",
        "caption" : {
          "created_time" : "1482648403",
          "from" : {
            "full_name" : "PARAMSahib ™",
            "profile_picture" : "https://scontent.cdninstagram.com/t51.2885-19/s150x150/12750236_1692144537739696_350427084_a.jpg",
            "id" : "1373991666",
            "username" : "parambanana"
          },
          "id" : "17845953787172829",
          "text" : "This feature talks about how to work pastels .\n\nDull gold pullover + saffron khadi kurta + baby pink pants + Deep purple patka and white sneakers - Perfect colours for a Happy sunday christmas morning . \n#paramsahib #men #menswear #mensfashion #mensfashionblog #mensfashionblogger #menswearofficial #menstyle #fashion #fashionfashion #fashionblog #blog #blogger #designer #fashiondesigner #streetstyle #streetfashion #sikh #sikhfashion #singhstreetstyle #sikhdesigner #bearded #indian #indianfashionblog #indiandesigner #international #ootd #lookbook #delhistyleblog #delhifashionblog"
        },
        "type" : "image",
        "tags" : [
          "men",
          "delhifashionblog",
          "menswearofficial",
          "fashiondesigner",
          "singhstreetstyle",
          "fashionblog",
          "mensfashion",
          "fashion",
          "sikhfashion",
          "delhistyleblog",
          "sikhdesigner",
          "indianfashionblog",
          "lookbook",
          "fashionfashion",
          "designer",
          "streetfashion",
          "international",
          "paramsahib",
          "mensfashionblogger",
          "indian",
          "blog",
          "mensfashionblog",
          "menstyle",
          "ootd",
          "indiandesigner",
          "menswear",
          "blogger",
          "sikh",
          "streetstyle",
          "bearded"
        ],
        "filter" : "Normal",
        "attribution" : null,
        "location" : null,
        "id" : "1412879673545024927_1373991666",
        "likes" : {
          "count" : 163
        }
      }
    }
  },

Answer 1

If your tags type in mapping is object (which is by default) you can use an aggregation query like this:

{
   "size": 0,
   "aggs": {
      "frequent_tags": {
         "terms": {"field": "post.tags"}
      }
   }
}