ELK聚和函数报错 Text fields are not optimised for operations that require per-document field data like ag

Elasticsearch权威指南里的聚合分析报错: 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 [price] in order to load field data by uninverting the inverted index. Note that this can use significant memory.

Elasticsearch权威指南是指官网的《Elasticsearch：权威指南》。

聚合分析

GET employee/_search
{
    "aggs": {
    "all_ages": {
      "terms": { "field": "age" }
    }
  }
}

GET employee/_search
{
    "aggs": {
    "all_interests": {
      "terms": { "field": "interests" }
    }
  }
}

在interests上进行聚合会报错，而age没问题。

"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."
  }
]

因为interests的type是text，而age不是， text或annotated_text字段doc_values默认为false。

简单理解，就是text字段作为一个整体，默认没有索引。

GET employee/_mapping
{
  "employee" : {
    "mappings" : {
      "properties" : {
        "about" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        },
        "age" : {
          "type" : "long"
        },
        "first_name" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        },
        "interests" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        },
        "last_name" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        }
      }
    }
  }
}

不过text分词之后的keyword是有索引的，因而可以对进行聚合。

GET employee/_search
{
    "aggs": {
    "all_interests": {
      "terms": { "field": "" }
    }
  }
}

也可以set fielddata=true，不过不推荐。

Fielddata is disabled on text fields by default.

Fielddata can consume a lot of heap space, especially when loading high cardinality text fields. Once fielddata has been loaded into the heap, it remains there for the lifetime of the segment. Also, loading fielddata is an expensive process which can cause users to experience latency hits. This is why fielddata is disabled by default.

PUT employee/_mapping 
{
  "properties": {
    "interests": {
      "type": "text",
      "fielddata": true
    }
  }
}

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