As fast as Elasticsearch is, it can be faster still. Combining multiple requests into one avoids the network overhead of processing each request individually. If you know that you need to retrieve multiple documents from Elasticsearch, it is faster to retrieve them all in a single request by using the multi-get, or mget, API, instead of document by document.

The mget API expects a docs array, each element of which specifies the _index, _type, and _id metadata of the document you wish to retrieve. You can also specify a _source parameter if you just want to retrieve one or more specific fields:

GET /_mget
{
   "docs" : [
      {
         "_index" : "website",
         "_type" :  "blog",
         "_id" :    2
      },
      {
         "_index" : "website",
         "_type" :  "pageviews",
         "_id" :    1,
         "_source": "views"
      }
   ]
}

The response body also contains a docs array that contains a response per document, in the same order as specified in the request. Each of these responses is the same response body that we would expect from an individual get request:

{
   "docs" : [
      {
         "_index" :   "website",
         "_id" :      "2",
         "_type" :    "blog",
         "found" :    true,
         "_source" : {
            "text" :  "This is a piece of cake...",
            "title" : "My first external blog entry"
         },
         "_version" : 10
      },
      {
         "_index" :   "website",
         "_id" :      "1",
         "_type" :    "pageviews",
         "found" :    true,
         "_version" : 2,
         "_source" : {
            "views" : 2
         }
      }
   ]
}

If the documents you wish to retrieve are all in the same _index (and maybe even of the same _type), you can specify a default /_index or a default /_index/_type in the URL.

You can still override these values in the individual requests:

GET /website/blog/_mget
{
   "docs" : [
      { "_id" : 2 },
      { "_type" : "pageviews", "_id" :   1 }
   ]
}

In fact, if all the documents have the same _index and _type, you can just pass an array of ids instead of the full docs array:

GET /website/blog/_mget
{
   "ids" : [ "2", "1" ]
}

Note that the second document that we requested doesn’t exist. We specified type blog, but the document with ID 1 is of type pageviews. This nonexistence is reported in the response body:

{
  "docs" : [
    {
      "_index" :   "website",
      "_type" :    "blog",
      "_id" :      "2",
      "_version" : 10,
      "found" :    true,
      "_source" : {
        "title":   "My first external blog entry",
        "text":    "This is a piece of cake..."
      }
    },
    {
      "_index" :   "website",
      "_type" :    "blog",
      "_id" :      "1",
      "found" :    false  
    }
  ]
}

The fact that the second document wasn’t found didn’t affect the retrieval of the first document. Each doc is retrieved and reported on individually.