在mapping index為true的情況下，該欄位會預設對內容進行分詞若進行agg操作則會出現下面情況：

命令：

GET  /data/http_record/_search
{
  "aggs": {
    "ua": {
      "terms": { "field": "user_agent" }
    }
  }
}

"aggregations": {
    "ua": {
      "doc_count_error_upper_bound": 204594,
      "sum_other_doc_count": 17127887,
      "buckets": [
        {
          "key": "android",
          "doc_count": 4574412
        },
        {
          "key": "build",
          "doc_count": 3761713
        },
        {
          "key": "vivo",
          "doc_count": 1116978
        },
        {
          "key": "5.1",
          "doc_count": 784951
        },
        {
          "key": "iphone",
          "doc_count": 674956
        },
        {
          "key": "4.4.4",
          "doc_count": 593027
        },
        {
          "key": "ios",
          "doc_count": 568399
        },
        {
          "key": "6.0",
          "doc_count": 524421
        },
        {
          "key": "5.1.1",
          "doc_count": 485652
        },
        {
          "key": "oppo",
          "doc_count": 471732
        }
      ]
    }
  }
}

GET  /data/http_record/_search
{
  "aggs": {
    "ua": {
      "terms": { "field": "user_agent.keyword" }
    }
  }
}

"aggregations": {
    "ua": {
      "doc_count_error_upper_bound": 26756,
      "sum_other_doc_count": 4667012,
      "buckets": [
        {
          "key": "iPhone; iOS 10.3.3; zh_CN)",
          "doc_count": 71982
        },
        {
          "key": "Android 3.3.1-R-20170728.1300; INPHIC_H3 Build/KOT49H)",
          "doc_count": 70493
        },
        {
          "key": "Android 5.1; OPPO A37m Build/LMY47I)",
          "doc_count": 67258
        },
        {
          "key": "Android 5.0.2; vivo Y33 Build/LRX21M)",
          "doc_count": 64267
        },
        {
          "key": "Android 4.3; Letv X3-43 Build/V2202RCN02C058050B10151S)",
          "doc_count": 64010
        },
        {
          "key": "Android 4.4.4; vivo Y23L Build/KTU84P)",
          "doc_count": 59655
        },
        {
          "key": "Android 5.1; F100 Build/LMY47D)",
          "doc_count": 51356
        },
        {
          "key": "Android 4.3; Letv S40 Air Build/V2202RCN02C058050B10151S)",
          "doc_count": 48992
        },
        {
          "key": "iPhone; iOS 10.3.3; Scale/2.00)",
          "doc_count": 46417
        },
        {
          "key": "Android 5.1.1; vivo Y51A Build/LMY47V)",
          "doc_count": 43156
        }
      ]
    }
  }
}