Fielddata is disabled on text fields by default. Set fielddata=true on [gender] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memor

ES进行如下聚合操作时，会报如题所示错误：

➜  Downloads curl -XPOST 'localhost:9200/bank/_search?pretty' -d '
        {
          "size": 0,
          "aggs": {
            "group_by_state": {
              "terms": {
                "field": "state"
              }
            }
          }
        }'

提示报错如下：

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Fielddata is disabled on text fields by default. Set fielddata=true on [state] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory."
      }
    ],
    "type" : "search_phase_execution_exception",
    "reason" : "all shards failed",
    "phase" : "query",
    "grouped" : true,
    "failed_shards" : [
      {
        "shard" : 0,
        "index" : "bank",
        "node" : "nkL8C69pTMuXrZBXicjshw",
        "reason" : {
          "type" : "illegal_argument_exception",
          "reason" : "Fielddata is disabled on text fields by default. Set fielddata=true on [state] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory."
        }
      }
    ],
    "caused_by" : {
      "type" : "illegal_argument_exception",
      "reason" : "Fielddata is disabled on text fields by default. Set fielddata=true on [state] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory."
    }
  },
  "status" : 400
}

　　根据官方文档显示，出现该错误是因为5.x之后，Elasticsearch对排序、聚合所依据的字段用单独的数据结构(fielddata)缓存到内存里了，但是在text字段上默认是禁用的，如果有需要单独开启，这样做的目的是为了节省内存空间。——官方文档地址：https://www.elastic.co/guide/en/elasticsearch/reference/current/fielddata.html

开启方法：

➜  Downloads curl -XPUT 'http://localhost:9200/bank/_mapping/account' -d '
{       
  "properties": {
        "state": {  
            "type": "text",
            "fielddata": true
        }       
    }         
}'
# bank是index、account是类型、state是你需要设置的text字段

出现如下提示，说明设置成功：

{"acknowledged":true}

至此，聚合问题解决：

➜  Downloads curl -XPOST 'localhost:9200/bank/_search?pretty' -d '        
        {
          "size": 0,
          "aggs": {
            "group_by_state": {
              "terms": {
                "field": "state"
              }
            }
          }
        }'
{
  "took" : 60,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 1000,
    "max_score" : 0.0,
    "hits" : [ ]
  },
  "aggregations" : {
    "group_by_state" : {
      "doc_count_error_upper_bound" : 20,
      "sum_other_doc_count" : 770,
      "buckets" : [
        {
          "key" : "id",
          "doc_count" : 27
        },
        {
          "key" : "tx",
          "doc_count" : 27
        },
        {
          "key" : "al",
          "doc_count" : 25
        },
        {
          "key" : "md",
          "doc_count" : 25
        },
        {
          "key" : "tn",
          "doc_count" : 23
        },
        {
          "key" : "ma",
          "doc_count" : 21
        },
        {
          "key" : "nc",
          "doc_count" : 21
        },
        {
          "key" : "nd",
          "doc_count" : 21
        },
        {
          "key" : "me",
          "doc_count" : 20
        },
        {
          "key" : "mo",
          "doc_count" : 20
        }
      ]
    }
  }
}