elasticsearch - only return specific fields without _source?

Question

I've found some answer like Make elasticsearch only return certain fields?

But they all need _source field.

In my system, disk and network are both scarce resources.

I can't store _source field and I don't need _index, _score field.

ElasticSearch Version: 5.5

Index Mapping just likes

{
  "index_2020-04-08": {
    "mappings": {
      "type1": {
        "_all": {
          "enabled": false
        },
        "_source": {
          "enabled": false
        },
        "properties": {
          "rank_score": {
            "type": "float"
          },
          "first_id": {
            "type": "keyword"
          },
          "second_id": {
            "type": "keyword"
          }
        }
      }
    }
  }
}

My query:

GET index_2020-04-08/type1/_search
{
  "query": {
    "bool": {
      "filter": {
        "term": {
          "first_id": "hello"
        }
      }
    }
  },
  "size": 1000,
  "sort": [
    {
      "rank_score": {
        "order": "desc"
      }
    }
  ]
}

The search results I got :

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": null,
    "hits": [
      {
        "_index": "index_2020-04-08",
        "_type": "type1",
        "_id": "id_1",
        "_score": null,
        "sort": [
          0.06621722
        ]
      },
      {
        "_index": "index_2020-04-08",
        "_type": "type1",
        "_id": "id_2",
        "_score": null,
        "sort": [
          0.07864579
        ]
      }
    ]
  }
}

The results I want:

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": null,
    "hits": [
      {
        "_id": "id_1"
      },
      {
        "_id": "id_2"
      }
    ]
  }
}

Can I implement it?

Answer 1

To return specific fields in the document, you must do one of the two:

1. Include the _source field in your documents, which is enabled by default.
2. Store specific fields with the stored fields feature which must be enabled manually

Because you want pretty much the document Ids and some metadata, you can use the filter_path feature.

Here's an example that's close to what you want (just change the field list):

$ curl -X GET "localhost:9200/metricbeat-7.6.1-2020.04.02-000002/_search?filter_path=took,timed_out,_shards,hits.total,hits.max_score,hits.hits._id&pretty"
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 10000,
      "relation" : "gte"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_id" : "8SEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "8iEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "8yEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "9CEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "9SEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "9iEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "9yEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "-CEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "-SEGSHEBzNscjCyQ18cg"
      },
      {
        "_id" : "-iEGSHEBzNscjCyQ18cg"
      }
    ]
  }
}