（54）ElasticSearch之DocValues解析

　　1、DocValues说明

　　DocValues其实是Lucene在构建倒排索引时，会额外建立一个有序的正排索引（基于document=>field value的映射列表）。年龄、日期等非字符型的可以排序，就是因为建立了倒排索引，也建立了正排索引。

　　DocValues说白了就是正排索引，默认对字符串类型的不起作用，即：默认对不分词的字段是开启的，对分词字段无效（需要把fielddata设置为true才可以）。

　　DocValues存储在磁盘上，节省内存，对排序，分组和一些聚合操作能够大大提升性能。

　　DocValues映射表如下：json文档字符串在磁盘上对应的是文档doc1和文档doc2，每一个字段都会列出

　　{"birthday":"1985-11-11",age:23}

　　{"birthday":"1989-11-11",age:29}

-----------------------------------------------------------

　　document　　age　　birthday

　　doc1　　        23　　 1985-11-11
　　doc2　　        29　　 1989-11-11

　　2、演示关闭age字段DocValues，执行排序搜索会报错

　　准备数据：

PUT /lib
{
    "settings":{
        "number_of_shards":3,
        "number_of_replicas":0
      },
        "mappings":{
            "user":{
                "properties":{
                    "name":{"type":"text"},
                    "address":{"type":"text"},
                    "age":{"type":"integer"},
                    "interests":{"type":"text"},
                    "birthday":{"type":"date"}
                }
            }
        }
}

put /lib/user/1
{
    "name":"zhaoliu",
    "address":"hei long jiang sheng tie ling shi",
    "age":50,
    "birthday":"1970-12-12",
    "interests":"xi huang hejiu,duanlian,lvyou"
}

put /lib/user/2
{
    "name":"zhaoming",
    "address":"bei jing hai dian qu qing he zhen",
    "age":20,
    "birthday":"1998-10-12",
    "interests":"xi huan hejiu,duanlian,changge"
}

put /lib/user/3
{
    "name":"lisi",
    "address":"bei jing hai dian qu qing he zhen",
    "age":23,
    "birthday":"1998-10-12",
    "interests":"xi huan hejiu,duanlian,changge"
}

put /lib/user/4
{
    "name":"wangwu",
    "address":"bei jing hai dian qu qing he zhen",
    "age":26,
    "birthday":"1998-10-12",
    "interests":"xi huan biancheng,tingyinyue,lvyou"
}

put /lib/user/5
{
    "name":"zhangsan",
    "address":"bei jing chao yang qu",
    "age":29,
    "birthday":"1988-10-12",
    "interests":"xi huan tingyinyue,changge,tiaowu"
}

　　现在没有关闭age字段DocValues，执行排序搜索正常

GET lib/user/_search
{
  "query": {
    "match_all": {}
  },
  "sort": [
    {
      "age": {
        "order": "desc"
      }
    }
  ]
}

　　查询结果：

{
  "took": 9,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 5,
    "max_score": null,
    "hits": [
      {
        "_index": "lib",
        "_type": "user",
        "_id": "1",
        "_score": null,
        "_source": {
          "name": "zhaoliu",
          "address": "hei long jiang sheng tie ling shi",
          "age": 50,
          "birthday": "1970-12-12",
          "interests": "xi huang hejiu,duanlian,lvyou"
        },
        "sort": [
          50
        ]
      },
      {
        "_index": "lib",
        "_type": "user",
        "_id": "5",
        "_score": null,
        "_source": {
          "name": "zhangsan",
          "address": "bei jing chao yang qu",
          "age": 29,
          "birthday": "1988-10-12",
          "interests": "xi huan tingyinyue,changge,tiaowu"
        },
        "sort": [
          29
        ]
      },
      {
        "_index": "lib",
        "_type": "user",
        "_id": "4",
        "_score": null,
        "_source": {
          "name": "wangwu",
          "address": "bei jing hai dian qu qing he zhen",
          "age": 26,
          "birthday": "1998-10-12",
          "interests": "xi huan biancheng,tingyinyue,lvyou"
        },
        "sort": [
          26
        ]
      },
      {
        "_index": "lib",
        "_type": "user",
        "_id": "3",
        "_score": null,
        "_source": {
          "name": "lisi",
          "address": "bei jing hai dian qu qing he zhen",
          "age": 23,
          "birthday": "1998-10-12",
          "interests": "xi huan hejiu,duanlian,changge"
        },
        "sort": [
          23
        ]
      },
      {
        "_index": "lib",
        "_type": "user",
        "_id": "2",
        "_score": null,
        "_source": {
          "name": "zhaoming",
          "address": "bei jing hai dian qu qing he zhen",
          "age": 20,
          "birthday": "1998-10-12",
          "interests": "xi huan hejiu,duanlian,changge"
        },
        "sort": [
          20
        ]
      }
    ]
  }
}

　　现在重新建立索引，并添加上面的数据、执行排序搜索报错

PUT /lib
{
    "settings":{
        "number_of_shards":3,
        "number_of_replicas":0
      },
        "mappings":{
            "user":{
                "properties":{
                    "name":{"type":"text"},
                    "address":{"type":"text"},
                    "age":{
                      "type":"integer",
                      "doc_values":false
                    },
                    "interests":{"type":"text"},
                    "birthday":{"type":"date"}
                }
            }
        }
}

　　执行查询

GET lib/user/_search
{
  "query": {
    "match_all": {}
  },
  "sort": [
    {
      "age": {
        "order": "desc"
      }
    }
  ]
}

　　查询结果，报错 

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Can't load fielddata on [age] because fielddata is unsupported on fields of type [integer]. Use doc values instead."
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "lib",
        "node": "AJ3x6yc8TfKj6_zx6VRm0g",
        "reason": {
          "type": "illegal_argument_exception",
          "reason": "Can't load fielddata on [age] because fielddata is unsupported on fields of type [integer]. Use doc values instead."
        }
      }
    ]
  },
  "status": 400
}

注意：

假如把age的doc values关闭，执行排序搜索会报错