How to reduce doc_count_error_upper_bound to 0

[Udayabharathi (Udayabharathi Thiagarajan)]

I'm new to elasticsearch and I recently came across this doc_count_error_upper_bound in the results. When I tried to aggregate the data using terms based on a field with sorting based on descending count and limited the data to size 10, I had doc_count_error_upper_bound as 10 on the result. This leads me to verify the correctness of the count data in the result. When I verified it was only approximate and not accurate. I came across the elasticsearch docs where I found that ES uses shards to store the data and I understood it is based on the size that the accuracy of the results varies. I can easily increase the size given to reduce the error upper bound. My question is whether we have a way to reduce the number of shards being used and if so, is reducing the number of shards used for accuracy the right way? Also, I want to know how the performance degrades when we reduce the shards? I've attached the query and the result too.

Query:

{
  "size": 0,
  "aggs": {
    "2": {
      "terms": {
        "field": "...",
        "order": {
          "_count": "desc"
        },
        "size": 10
      }
    }
  },
  "_source": {},
  "sort": [ ],
  "query": {
    "constant_score": {
      "filter": {
        "bool": {
          "must": [
            ...
          ],
          "should": [],
          "must_not": [
            ...
          ]
        }
      }
    }
  }
}

Response:

  {
  "took" : 7,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 7692,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "2" : {
      "doc_count_error_upper_bound" : 15,
      "sum_other_doc_count" : 6596,
      "buckets" : [
        ...
      ]
    }
  }
}