How does Kibana calculate metric values for other bucket?

README.md

How does Kibana calculate metric values for other bucket?

In order to render the Other slice, Kibana uses the sum_other_doc_count value in the response. That works if the metric is Count. But what if we use different metric aggretation to define the size of each slice?

For example, this pie chart uses sum of field age. But still, Kibana is able to show the Other slice as expected.

When I looked at Chrome dev tool network tab, there were 2 _search requests shown as below. Kibana sends the 2nd request to get the metric value for the Other slice.

The 2nd request uses bool query must_not clause to exclude the top terms.

1st request

{
  "aggs": {
    "2": {
      "terms": {
        "field": "occupation.keyword",
        "order": {
          "1": "desc"
        },
        "size": 2
      },
      "aggs": {
        "1": {
          "sum": {
            "field": "age"
          }
        }
      }
    }
  },
  "size": 0,
  "stored_fields": [
    "*"
  ],
  "script_fields": {},
  "docvalue_fields": [],
  "_source": {
    "excludes": []
  },
  "query": {
    "bool": {
      "must": [],
      "filter": [],
      "should": [],
      "must_not": []
    }
  }
}

1st response

{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 5000,
    "max_score": null,
    "hits": []
  },
  "aggregations": {
    "2": {
      "doc_count_error_upper_bound": -1,
      "sum_other_doc_count": 2188,
      "buckets": [
        {
          "1": {
            "value": 65817
          },
          "key": "Software Engineer",
          "doc_count": 1785
        },
        {
          "1": {
            "value": 37848
          },
          "key": "Sales",
          "doc_count": 1027
        }
      ]
    }
  }
}

2nd request

{
  "aggs": {
    "other-filter": {
      "aggs": {
        "1": {
          "sum": {
            "field": "age"
          }
        }
      },
      "filters": {
        "filters": {
          "": {
            "bool": {
              "must": [],
              "filter": [
                {
                  "exists": {
                    "field": "occupation.keyword"
                  }
                }
              ],
              "should": [],
              "must_not": [
                {
                  "match_phrase": {
                    "occupation.keyword": "Software Engineer"
                  }
                },
                {
                  "match_phrase": {
                    "occupation.keyword": "Sales"
                  }
                }
              ]
            }
          }
        }
      }
    }
  },
  "size": 0,
  "stored_fields": [
    "*"
  ],
  "script_fields": {},
  "docvalue_fields": [],
  "_source": {
    "excludes": []
  },
  "query": {
    "bool": {
      "must": [],
      "filter": [],
      "should": [],
      "must_not": []
    }
  }
}

2nd response

{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 5000,
    "max_score": null,
    "hits": []
  },
  "aggregations": {
    "other-filter": {
      "buckets": {
        "": {
          "1": {
            "value": 80922
          },
          "doc_count": 2188
        }
      }
    }
  }
}

other-metric.png