The Search APIedit

Now let’s start with some simple searches. There are two basic ways to run searches: one is by sending search parameters through the REST request URI and the other by sending them through the REST request body. The request body method allows you to be more expressive and also to define your searches in a more readable JSON format. We’ll try one example of the request URI method but for the remainder of this tutorial, we will exclusively be using the request body method.

The REST API for search is accessible from the _search endpoint. This example returns all documents in the bank index:

GET /bank/_search?q=*&sort=account_number:asc&pretty

Let’s first dissect the search call. We are searching (_search endpoint) in the bank index, and the q=* parameter instructs Elasticsearch to match all documents in the index. The sort=account_number:asc parameter indicates to sort the results using the account_number field of each document in an ascending order. The pretty parameter, again, just tells Elasticsearch to return pretty-printed JSON results.

And the response (partially shown):

{
  "took" : 63,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
        "value": 1000,
        "relation": "eq"
    },
    "max_score" : null,
    "hits" : [ {
      "_index" : "bank",
      "_type" : "_doc",
      "_id" : "0",
      "sort": [0],
      "_score" : null,
      "_source" : {"account_number":0,"balance":16623,"firstname":"Bradshaw","lastname":"Mckenzie","age":29,"gender":"F","address":"244 Columbus Place","employer":"Euron","email":"bradshawmckenzie@euron.com","city":"Hobucken","state":"CO"}
    }, {
      "_index" : "bank",
      "_type" : "_doc",
      "_id" : "1",
      "sort": [1],
      "_score" : null,
      "_source" : {"account_number":1,"balance":39225,"firstname":"Amber","lastname":"Duke","age":32,"gender":"M","address":"880 Holmes Lane","employer":"Pyrami","email":"amberduke@pyrami.com","city":"Brogan","state":"IL"}
    }, ...
    ]
  }
}

As for the response, we see the following parts:

  • took – time in milliseconds for Elasticsearch to execute the search
  • timed_out – tells us if the search timed out or not
  • _shards – tells us how many shards were searched, as well as a count of the successful/failed searched shards
  • hits – search results
  • hits.total – an object that contains information about the total number of documents matching our search criteria

    • hits.total.value - the value of the total hit count (must be interpreted in the context of hits.total.relation).
    • hits.total.relation - whether hits.total.value is the exact hit count, in which case it is equal to "eq" or a lower bound of the total hit count (greater than or equals), in which case it is equal to gte.
  • hits.hits – actual array of search results (defaults to first 10 documents)
  • hits.sort - sort key for results (missing if sorting by score)
  • hits._score and max_score - ignore these fields for now

The accuracy of hits.total is controlled by the request parameter track_total_hits, when set to true the request will track the total hits accurately ("relation": "eq"). It defaults to 10,000 which means that the total hit count is accurately tracked up to 10,000 documents. You can force an accurate count by setting track_total_hits to true explicitly. See the request body documentation for more details.

Here is the same exact search above using the alternative request body method:

GET /bank/_search
{
  "query": { "match_all": {} },
  "sort": [
    { "account_number": "asc" }
  ]
}

The difference here is that instead of passing q=* in the URI, we provide a JSON-style query request body to the _search API. We’ll discuss this JSON query in the next section.

It is important to understand that once you get your search results back, Elasticsearch is completely done with the request and does not maintain any kind of server-side resources or open cursors into your results. This is in stark contrast to many other platforms such as SQL wherein you may initially get a partial subset of your query results up-front and then you have to continuously go back to the server if you want to fetch (or page through) the rest of the results using some kind of stateful server-side cursor.