elastic使用时报错Text fields are not optimised for operations that require per-document field data

一、elasticsearch在做聚合查询的时候报错

"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."
      }
    ]

发送的DSL语句如下：

GET rest_logs-*/_search
{
  "aggs": {
    "my-agg-name": {
      "terms": {
        "field": "requestUrl"
      }
    }
  },
  "size": 0
}

查询结果：

"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 [requestUrl] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
      }]

产生该错误的原因是因为该字段不支持聚合或者排序。由于 requestUrl的字段值在存储的时候进行分词了，假设 requestUrl的值为 “music forestry sports” 会被拆分为 music 、forestry 、sports 并建立倒排索引进行存储，如果我们使用 requestUrl 进行聚合或者排序操作，es并不知道要拿什么值去进行聚合或者排序。

所以为了解决这个问题，es也提供了两种解决方案：
1、用两种方式对同一个字符串进行索引，在文档中包括两个字段： analyzed 用于搜索，not_analyzed 用于排序或者聚合，但是保存相同的字符串两次在 _source 字段是浪费空间的。 我们真正想要做的是传递一个 单字段 但是却用两种方式索引它。所有的 _core_field 类型 (strings, numbers, Booleans, dates) 接收一个 fields 参数，故有了第二种方案。

2、为字段添加一个映射
原来的映射关系，这种直接使用 requestUrl 会报上述错误

"requestUrl": {
    "type":     "string",
    "analyzer": "english"
}

直接添加映射

"requestUrl": { 
    "type":     "string",
    "analyzer": "english",
    "fields": {
        "keyword": { 
            "type":  "string",
            "index": "not_analyzed"
        }
    }
}

然后重新查询，完美解决。

GET rest_logs-*/_search
{
  "aggs": {
    "my-agg-name": {
      "terms": {
        "field": "requestUrl.keyword"
      }
    }
  },
  "size": 0
}

https://blog.csdn.net/wngpenghao/article/details/123001881

https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations.html