elasticsearch使用aggs聚合时报错

问题：

GET /megacorp/employee/_search
{
  "aggs": {
    "all_interests": {
      "terms": { "field": "interests" }
    }
  }
}

kibana中输入以上内容时报错：

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [interests] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
      }
    ],
    "type" : "search_phase_execution_exception",
    "reason" : "all shards failed",
    "phase" : "query",
    "grouped" : true,
    "failed_shards" : [
      {
        "shard" : 0,
        "index" : "megacorp",
        "node" : "EzyH308RT0iU4WNgOa2J5Q",
        "reason" : {
          "type" : "illegal_argument_exception",
          "reason" : "Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [interests] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
        }
      }
    ],
    "caused_by" : {
      "type" : "illegal_argument_exception",
      "reason" : "Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [interests] in order to load field data by uninverting the inverted index. Note that this can use significant memory.",
      "caused_by" : {
        "type" : "illegal_argument_exception",
        "reason" : "Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [interests] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
      }
    }
  },
  "status" : 400
}

原因：

fielddata在text字段中默认未启用
因为fielddata会消耗大量的堆内存,特别是当加载大量的text字段时;fielddata一旦加载到堆中,在segment的生命周期之内都将一直保持在堆中,另外加载fielddata也是一个比较耗时的过程,这可能会导致用户遇到延迟,故而默认情况下禁用fielddata参数

解决办法：

PUT /megacorp/_mapping
{
  "properties": {
    "interests": { 
      "type":     "text",
      "fielddata": true
    }
  }
}