Elasticsearch之常见问题

　　一. 聚合操作时，报Fielddata is disabled on text fields by default

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


{ "error": { "root_cause": [ { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] 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." } ], "type": "search_phase_execution_exception", "reason": "all shards failed", "phase": "query", "grouped": true, "failed_shards": [ { "shard": 0, "index": "megacorp", "node": "sNvWT__lQl6p0dMTRaAOAg", "reason": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] 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." } } ], "caused_by": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] 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.", "caused_by": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] 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." } } }, "status": 400 }

text类型的字段在查询时使用的是在内存中的称为fielddata的数据结构。这种数据结构是在第一次将字段用于聚合/排序/脚本时基于需求建立的。

它通过读取磁盘上每个segmet上所有的倒排索引来构建，反转term和document的关系(倒排)，并将结果存在Java堆上(内存中)。(因此会耗费很多的堆空间，特别是在加载很高基数的text字段时)。一旦fielddata被加载到堆中，它在segment中的生命周期还是存在的。

因此，加载fielddata是一个非常消耗资源的过程，甚至能导致用户体验到延迟.这就是为什么 fielddata 默认关闭。

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

标签：interests,use,常见问题,fielddata,text,reason,Elasticsearch,memory
来源： https://www.cnblogs.com/xingxia/p/elasticsearch_problems.html