ES聚合操作 – Fielddata is disabled on text fields by default

使用ES聚合操作对字段(projectCode)去重：

GET bury-point-click/_search
{
  "size": 0,
  "aggs": {
    "group_by_project": {
      "cardinality": {
        "field": "projectCode"
      }
    }
  }
}

执行报错：Fielddata is disabled on text fields by default. Set fielddata=true on [projectCode] 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.

这是因为ES对排序，聚合这些操作用单独的数据结构(fielddata)缓存到内存里，Text字段数据会占用大量堆空间，需要单独开启。

开启代码如下：

PUT bury-point-click/_mapping/
{
  "properties": {
    "projectCode": { 
      "type":     "text",
      "fielddata": true
    }
  }
}

再执行原来的语句，正常返回结果。

参考

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