ElasticSearch 在排序操作時報錯: Fielddata is disabled on text fields by default...

1. 異常信息:

   Fielddata is disabled on text fields by default. Set fielddata=true on [my_field] 
   in order to load fielddata in memory by uninverting the inverted index. 
   Note that this can however use significant memory. Alternatively use a keyword field instead.
   

2. 解決辦法:

   默認情況下 text 字段的 Fielddata 是禁用的。如果對 text 字段中的進行排序，彙總或訪問值，則會看到上述異常。
   可以對 text 字段上啓用 Fielddata 解決。

   curl -X PUT "localhost:9200/my_index/_mapping?pretty" -H 'Content-Type: application/json' -d'
   {
     "properties": {
       "my_field": { 
         "type":     "text",
         "fielddata": true
       }
     }
   }
   '
   

參考: https://www.elastic.co/guide/en/elasticsearch/reference/current/fielddata.html