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
         }
       ]
     }
   }
 }