Elasticsearch 6.2.3版本 string 类型字段 排序 报错 Fielddata is disabled on text fields by default

背景说明

最近在做一个 Elasticsearch 的分页查询，并且对查询结果按照特定字段进行排序的功能。

但是执行结果却报错，报错信息如下：

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [state] 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": "alarm",
        "node": "hdLJanxRTbmF52eK6-FFgg",
        "reason": {
          "type": "illegal_argument_exception",
          "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [state] 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
}

原因分析

查询语句如下：

GET alarm/_search           // index为 alarm
{
  "query" : {
    "bool" : {
      "must" : [
        {
          "match_phrase" : {
            "state" : {
              "query" : "confirmed",
              "slop" : 0,
              "boost" : 1.0
            }
          }
        }
      ],
      "disable_coord" : false,
      "adjust_pure_negative" : true,
      "boost" : 1.0
    }
  },
  "from": 1,   // 分页，第几页开始
  "size": 5,    // 分页，每页显示多少条
  "sort": {    // 排序，按照  state 字段降序排序
    "state": {
      "order": "desc"

    }
  }
}

测试分析：

1）去除排序语句，分页查询是OK的，问题出在了排序字段；

2）按照 integer 类型 或者 date 类型的字段排序都是OK的，但是 string 类型排序报错（示例中的state字段为 string 类型）

解决方案

其实在报错信息里已经提供了解决方案：

需要对 string类型的字段，单独设置加载到内存中，才能排序。

Set fielddata=true on [state] in order to load fielddata in memory by uninverting the inverted index. 

具体设置操作如下：

PUT alarm/_mapping/alarmInfoHistory/
{
    "properties":{
        "state":{
            "type":"text",
            "fielddata":true
        }
    }
}

执行结果：

{
  "acknowledged": true
}

再次执行排序查询查询语句，就OK了。

Good Luck~

PS：

如果想按照多个字段排序（按照 state 和 alarmGrade 降序排序），SQL参考如下：

{
    "query":{
        "bool":{
            "must":[
                {
                    "match_phrase":{
                        "state":{
                            "query":"confirmed",
                            "slop":0,
                            "boost":1
                        }
                    }
                }
            ],
            "disable_coord":false,
            "adjust_pure_negative":true,
            "boost":1
        }
    },
    "from":1,
    "size":10,
    "sort":[
        {
            "state":{
                "order":"desc"
            }
        },
        {
            "alarmGrade":{
                "order":"desc"
            }
        }
    ]
}