ElasticSearch（六）：聚合索引

• ElasticSearch聚合操作
  • 聚合的分类
  • Metric Aggregation
  • Bucket Aggregation
  • Pipeline Aggregation
  • 聚合的作用范围
  • 排序
• Elasticsearch 聚合性能优化
  • ES聚合分析不精准原因分析
  • 启用 eager global ordinals 提升高基数聚合性能
  • 插入数据时对索引进行预排序
  • 使用节点查询缓存
  • 使用分片请求缓存
  • 拆分聚合，使聚合并行化

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

语法：

"aggs" : { #和query同级的关键词
    "" : { #自定义的聚合名字
        "" : { #聚合的定义： 不同的type+body
            <aggregation_body>
        }
        [,"meta" : {  [<meta_data_body>] } ]?
        [,"aggregations" : { [<sub_aggregation>]+ } ]?  #子聚合查询
    }
    [,"" : { ... } ]*  #可以包含多个同级的聚合查询
}

聚合的分类

Metric Aggregation：—些数学运算，可以对文档字段进行统计分析，类比Mysql中的 min(), max(), sum() 操作。

SELECT MIN(price), MAX(price) FROM products
#Metric聚合的DSL类比实现：
{
    "aggs":{
        "avg_price":{
            "avg":{
                "field":"price"
            }
        }
    }
}

• 单值分析︰只输出一个分析结果
  • min, max, avg, sum
  • Cardinality（类似distinct Count)
• 多值分析:输出多个分析结果
  • stats（统计）, extended stats
  • percentile （百分位）, percentile rank
  • top hits(排在前面的示例)

多个 Metric 聚合，找到最低最高和平均工资

#"size": 0 只返回统计结果
POST /employees/_search
{
  "size": 0,
  "aggs": {
    "max_salary": {
      "max": {
        "field": "salary"
      }
    },
    "min_salary": {
      "min": {
        "field": "salary"
      }
    },
    "avg_salary": {
      "avg": {
        "field": "salary"
      }
    }
  }
}
response
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "max_salary" : {
      "value" : 50000.0
    },
    "avg_salary" : {
      "value" : 24700.0
    },
    "min_salary" : {
      "value" : 9000.0
    }
  }
}

对salary进行统计 stats

POST /employees/_search
{
  "size": 0,
  "aggs": {
    "stats_salary": {
      "stats": {
        "field": "salary"
      }
    }
  }
}
response
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "stats_salary" : {
      "count" : 20,
      "min" : 9000.0,
      "max" : 50000.0,
      "avg" : 24700.0,
      "sum" : 494000.0
    }
  }
}

cardinate对搜索结果去重

POST /employees/_search
{
  "size": 0,
  "aggs": {
    "cardinate": {
      "cardinality": {
        "field": "job.keyword"
      }
    }
  }
}
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "cardinate" : {
      "value" : 7
    }
  }
}

Bucket Aggregation： 一些满足特定条件的文档的集合放置到一个桶里，每一个桶关联一个key，类比Mysql中的group by操作。

SELECT size COUNT(*) FROM products GROUP BY size
#bucket聚合的DSL类比实现：
{
 "aggs": {
    "by_size": {
      "terms": {
        "field": "size"
      }
  }
}

按照一定的规则，将文档分配到不同的桶中，从而达到分类的目的。ES提供的一些常见的 Bucket Aggregation

• Terms，需要字段支持filedata

• keyword 默认支持fielddata
• text需要在Mapping 中开启fielddata，会按照分词后的结果进行分桶

• 数字类型

• Range / Data Range
• Histogram（直方图） / Date Histogram

• 支持嵌套: 也就在桶里再做分桶

获取job的分类信息 field、size、order

聚合可配置属性有：

• field：指定聚合字段
• size：指定聚合结果数量
• order：指定聚合结果排序方式

默认情况下，Bucket聚合会统计Bucket内的文档数量，记为_count，并且按照_count降序排序。我们可以指定order属性，自定义聚合的排序方式：

# 对keword 进行聚合
# 对keword 进行聚合
GET /employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword",
        "size": 10,
        "order": {
          "_count": "desc"
        }
      }
    }
  }
}
response
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "jobs" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4
        },
        {
          "key" : "QA",
          "doc_count" : 3
        },
        {
          "key" : "DBA",
          "doc_count" : 2
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2
        },
        {
          "key" : "Dev Manager",
          "doc_count" : 1
        },
        {
          "key" : "Product Manager",
          "doc_count" : 1
        }
      ]
    }
  }
}

限定聚合范围

#只对salary在10000元以上的文档聚合
GET /employees/_search
{
  "query": {
    "range": {
      "salary": {
        "gte": 10000 
      }
    }
  }, 
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword",
         "size": 10,
        "order": {
          "_count": "desc" 
        }
      }
    }
  }
}

对 Text 字段进行 terms 聚合查询，会失败抛出异常

POST /employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job"
      }
    }
  }
}
response
{
  "error" : {
    "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 [job] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
      }
    ],
    "type" : "search_phase_execution_exception",
    "reason" : "all shards failed",
    "phase" : "query",
    "grouped" : true,
    "failed_shards" : [
      {
        "shard" : 0,
        "index" : "employees",
        "node" : "rEYg9XpfS_uCtGpHpeoSCw",
        "reason" : {
          "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 [job] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
        }
      }
    ],
    "caused_by" : {
      "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 [job] in order to load field data by uninverting the inverted index. Note that this can use significant memory.",
      "caused_by" : {
        "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 [job] in order to load field data by uninverting the inverted index. Note that this can use significant memory."
      }
    }
  },
  "status" : 400
}

解决办法：对 Text 字段打开 fielddata，支持terms aggregation

PUT /employees/_mapping
{
  "properties" : {
    "job":{
       "type":  "text",
       "fielddata": true
    }
  }
}

对job.keyword 和 job 进行 terms 聚合，分桶的总数并不一样

terms

POST /employees/_search
{
  "size": 0,
  "aggs": {
    "cardinate": {
      "cardinality": {
        "field": "job"
      }
    }
  }
}
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "cardinate" : {
      "value" : 10
    }
  }
}

keyword

POST /employees/_search
{
  "size": 0,
  "aggs": {
    "cardinate": {
      "cardinality": {
        "field": "job.keyword"
      }
    }
  }
}
response
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "cardinate" : {
      "value" : 7
    }
  }
}

Range & Histogram聚合

• 按照数字的范围，进行分桶
• 在Range Aggregation中，可以自定义Key

Range 示例：按照工资的 Range 分桶

POST employees/_search
{
  "size": 0,
  "aggs": {
    "salary_range": {
      "range": {
        "field":"salary",
        "ranges":[
          {
            "to":10000
          },
          {
            "from":10000,
            "to":20000
          },
          {
            "key":">20000",
            "from":20000
          }
        ]
      }
    }
  }
}
response
{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "salary_range" : {
      "buckets" : [
        {
          "key" : "*-10000.0",
          "to" : 10000.0,
          "doc_count" : 1
        },
        {
          "key" : "10000.0-20000.0",
          "from" : 10000.0,
          "to" : 20000.0,
          "doc_count" : 4
        },
        {
          "key" : ">20000",
          "from" : 20000.0,
          "doc_count" : 15
        }
      ]
    }
  }
}

Histogram示例：按照工资的间隔分桶

#工资0到10万，以 5000一个区间进行分桶

POST employees/_search
{
  "size": 0,
  "aggs": {
    "salary_histrogram": {
      "histogram": {
        "field":"salary",
        "interval":5000,
        "extended_bounds":{
          "min":0,
          "max":100000
        }
      }
    }
  }
}
response
{
  "took" : 5,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "salary_histrogram" : {
      "buckets" : [
        {
          "key" : 0.0,
          "doc_count" : 0
        },
        {
          "key" : 5000.0,
          "doc_count" : 1
        },
        {
          "key" : 10000.0,
          "doc_count" : 0
        },
        {
          "key" : 15000.0,
          "doc_count" : 4
        },
        {
          "key" : 20000.0,
          "doc_count" : 6
        },
        {
          "key" : 25000.0,
          "doc_count" : 3
        },
        {
          "key" : 30000.0,
          "doc_count" : 3
        },
        {
          "key" : 35000.0,
          "doc_count" : 2
        },
        {
          "key" : 40000.0,
          "doc_count" : 0
        },
        {
          "key" : 45000.0,
          "doc_count" : 0
        },
        {
          "key" : 50000.0,
          "doc_count" : 1
        },
        {
          "key" : 55000.0,
          "doc_count" : 0
        },
        {
          "key" : 60000.0,
          "doc_count" : 0
        },
        {
          "key" : 65000.0,
          "doc_count" : 0
        },
        {
          "key" : 70000.0,
          "doc_count" : 0
        },
        {
          "key" : 75000.0,
          "doc_count" : 0
        },
        {
          "key" : 80000.0,
          "doc_count" : 0
        },
        {
          "key" : 85000.0,
          "doc_count" : 0
        },
        {
          "key" : 90000.0,
          "doc_count" : 0
        },
        {
          "key" : 95000.0,
          "doc_count" : 0
        },
        {
          "key" : 100000.0,
          "doc_count" : 0
        }
      ]
    }
  }
}

top_hits应用场景: 当获取分桶后，桶内最匹配的顶部文档列表

# 指定size，不同工种中，年纪最大的3个员工的具体信息
POST /employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword"
      },
      "aggs":{
        "old_employee":{
          "top_hits":{
            "size":3,
            "sort":[
              {
                "age":{
                  "order":"desc"
                }
              }
            ]
          }
        }
      }
    }
  }
}

response
{
  "took" : 5,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "jobs" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 7,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "11",
                  "_score" : null,
                  "_source" : {
                    "name" : "Jenny",
                    "age" : 36,
                    "job" : "Java Programmer",
                    "gender" : "female",
                    "salary" : 38000
                  },
                  "sort" : [
                    36
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "15",
                  "_score" : null,
                  "_source" : {
                    "name" : "King",
                    "age" : 33,
                    "job" : "Java Programmer",
                    "gender" : "male",
                    "salary" : 28000
                  },
                  "sort" : [
                    33
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "9",
                  "_score" : null,
                  "_source" : {
                    "name" : "Gregory",
                    "age" : 32,
                    "job" : "Java Programmer",
                    "gender" : "male",
                    "salary" : 22000
                  },
                  "sort" : [
                    32
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 4,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "14",
                  "_score" : null,
                  "_source" : {
                    "name" : "Marshall",
                    "age" : 32,
                    "job" : "Javascript Programmer",
                    "gender" : "male",
                    "salary" : 25000
                  },
                  "sort" : [
                    32
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "18",
                  "_score" : null,
                  "_source" : {
                    "name" : "Catherine",
                    "age" : 29,
                    "job" : "Javascript Programmer",
                    "gender" : "female",
                    "salary" : 20000
                  },
                  "sort" : [
                    29
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "17",
                  "_score" : null,
                  "_source" : {
                    "name" : "Goodwin",
                    "age" : 25,
                    "job" : "Javascript Programmer",
                    "gender" : "male",
                    "salary" : 16000
                  },
                  "sort" : [
                    25
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 3,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "6",
                  "_score" : null,
                  "_source" : {
                    "name" : "Lucy",
                    "age" : 31,
                    "job" : "QA",
                    "gender" : "female",
                    "salary" : 25000
                  },
                  "sort" : [
                    31
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "7",
                  "_score" : null,
                  "_source" : {
                    "name" : "Byrd",
                    "age" : 27,
                    "job" : "QA",
                    "gender" : "male",
                    "salary" : 20000
                  },
                  "sort" : [
                    27
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "5",
                  "_score" : null,
                  "_source" : {
                    "name" : "Rose",
                    "age" : 25,
                    "job" : "QA",
                    "gender" : "female",
                    "salary" : 18000
                  },
                  "sort" : [
                    25
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "19",
                  "_score" : null,
                  "_source" : {
                    "name" : "Boone",
                    "age" : 30,
                    "job" : "DBA",
                    "gender" : "male",
                    "salary" : 30000
                  },
                  "sort" : [
                    30
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "20",
                  "_score" : null,
                  "_source" : {
                    "name" : "Kathy",
                    "age" : 29,
                    "job" : "DBA",
                    "gender" : "female",
                    "salary" : 20000
                  },
                  "sort" : [
                    29
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "4",
                  "_score" : null,
                  "_source" : {
                    "name" : "Rivera",
                    "age" : 26,
                    "job" : "Web Designer",
                    "gender" : "female",
                    "salary" : 22000
                  },
                  "sort" : [
                    26
                  ]
                },
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "3",
                  "_score" : null,
                  "_source" : {
                    "name" : "Tran",
                    "age" : 25,
                    "job" : "Web Designer",
                    "gender" : "male",
                    "salary" : 18000
                  },
                  "sort" : [
                    25
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "Dev Manager",
          "doc_count" : 1,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 1,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "2",
                  "_score" : null,
                  "_source" : {
                    "name" : "Underwood",
                    "age" : 41,
                    "job" : "Dev Manager",
                    "gender" : "male",
                    "salary" : 50000
                  },
                  "sort" : [
                    41
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "Product Manager",
          "doc_count" : 1,
          "old_employee" : {
            "hits" : {
              "total" : {
                "value" : 1,
                "relation" : "eq"
              },
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "employees",
                  "_type" : "_doc",
                  "_id" : "1",
                  "_score" : null,
                  "_source" : {
                    "name" : "Emma",
                    "age" : 32,
                    "job" : "Product Manager",
                    "gender" : "female",
                    "salary" : 35000
                  },
                  "sort" : [
                    32
                  ]
                }
              ]
            }
          }
        }
      ]
    }
  }
}

嵌套聚合示例

嵌套聚合1，按照工作类型分桶，并统计工资信息

POST employees/_search
{
  "size": 0,
  "aggs": {
    "Job_salary_stats": {
      "terms": {
        "field": "job.keyword"
      },
      "aggs": {
        "salary": {
          "stats": {
            "field": "salary"
          }
        }
      }
    }
  }
}

response
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "Job_salary_stats" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "salary" : {
            "count" : 7,
            "min" : 9000.0,
            "max" : 38000.0,
            "avg" : 25571.428571428572,
            "sum" : 179000.0
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "salary" : {
            "count" : 4,
            "min" : 16000.0,
            "max" : 25000.0,
            "avg" : 19250.0,
            "sum" : 77000.0
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "salary" : {
            "count" : 3,
            "min" : 18000.0,
            "max" : 25000.0,
            "avg" : 21000.0,
            "sum" : 63000.0
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "salary" : {
            "count" : 2,
            "min" : 20000.0,
            "max" : 30000.0,
            "avg" : 25000.0,
            "sum" : 50000.0
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "salary" : {
            "count" : 2,
            "min" : 18000.0,
            "max" : 22000.0,
            "avg" : 20000.0,
            "sum" : 40000.0
          }
        },
        {
          "key" : "Dev Manager",
          "doc_count" : 1,
          "salary" : {
            "count" : 1,
            "min" : 50000.0,
            "max" : 50000.0,
            "avg" : 50000.0,
            "sum" : 50000.0
          }
        },
        {
          "key" : "Product Manager",
          "doc_count" : 1,
          "salary" : {
            "count" : 1,
            "min" : 35000.0,
            "max" : 35000.0,
            "avg" : 35000.0,
            "sum" : 35000.0
          }
        }
      ]
    }
  }
}

多次嵌套。根据工作类型分桶，然后按照性别分桶，计算工资的统计信息

# 多次嵌套。根据工作类型分桶，然后按照性别分桶，计算工资的统计信息
POST employees/_search
{
  "size": 0,
  "aggs": {
    "Job_gender_stats": {
      "terms": {
        "field": "job.keyword"
      },
      "aggs": {
        "gender_stats": {
          "terms": {
            "field": "gender"
          },
          "aggs": {
            "salary_stats": {
              "stats": {
                "field": "salary"
              }
            }
          }
        }
      }
    }
  }
}
response
{
  "took" : 2,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "Job_gender_stats" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "male",
                "doc_count" : 5,
                "salary_stats" : {
                  "count" : 5,
                  "min" : 9000.0,
                  "max" : 32000.0,
                  "avg" : 22200.0,
                  "sum" : 111000.0
                }
              },
              {
                "key" : "female",
                "doc_count" : 2,
                "salary_stats" : {
                  "count" : 2,
                  "min" : 30000.0,
                  "max" : 38000.0,
                  "avg" : 34000.0,
                  "sum" : 68000.0
                }
              }
            ]
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "male",
                "doc_count" : 3,
                "salary_stats" : {
                  "count" : 3,
                  "min" : 16000.0,
                  "max" : 25000.0,
                  "avg" : 19000.0,
                  "sum" : 57000.0
                }
              },
              {
                "key" : "female",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 20000.0,
                  "max" : 20000.0,
                  "avg" : 20000.0,
                  "sum" : 20000.0
                }
              }
            ]
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "female",
                "doc_count" : 2,
                "salary_stats" : {
                  "count" : 2,
                  "min" : 18000.0,
                  "max" : 25000.0,
                  "avg" : 21500.0,
                  "sum" : 43000.0
                }
              },
              {
                "key" : "male",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 20000.0,
                  "max" : 20000.0,
                  "avg" : 20000.0,
                  "sum" : 20000.0
                }
              }
            ]
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "female",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 20000.0,
                  "max" : 20000.0,
                  "avg" : 20000.0,
                  "sum" : 20000.0
                }
              },
              {
                "key" : "male",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 30000.0,
                  "max" : 30000.0,
                  "avg" : 30000.0,
                  "sum" : 30000.0
                }
              }
            ]
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "female",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 22000.0,
                  "max" : 22000.0,
                  "avg" : 22000.0,
                  "sum" : 22000.0
                }
              },
              {
                "key" : "male",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 18000.0,
                  "max" : 18000.0,
                  "avg" : 18000.0,
                  "sum" : 18000.0
                }
              }
            ]
          }
        },
        {
          "key" : "Dev Manager",
          "doc_count" : 1,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "male",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 50000.0,
                  "max" : 50000.0,
                  "avg" : 50000.0,
                  "sum" : 50000.0
                }
              }
            ]
          }
        },
        {
          "key" : "Product Manager",
          "doc_count" : 1,
          "gender_stats" : {
            "doc_count_error_upper_bound" : 0,
            "sum_other_doc_count" : 0,
            "buckets" : [
              {
                "key" : "female",
                "doc_count" : 1,
                "salary_stats" : {
                  "count" : 1,
                  "min" : 35000.0,
                  "max" : 35000.0,
                  "avg" : 35000.0,
                  "sum" : 35000.0
                }
              }
            ]
          }
        }
      ]
    }
  }
}

Pipeline Aggregation：对其他的聚合结果进行二次聚合

支持对聚合分析的结果，再次进行聚合分析。

Pipeline 的分析结果会输出到原结果中，根据位置的不同，分为两类：

• Sibling - 结果和现有分析结果同级
  • Max，min，Avg & Sum Bucket
  • Stats，Extended Status Bucket
  • Percentiles Bucket
• Parent -结果内嵌到现有的聚合分析结果之中
  • Derivative(求导)
  • Cumultive Sum(累计求和)
  • Moving Function(移动平均值 )

min_bucket示例 在员工数最多的工种里，找出平均工资最低的工种

• min_salary_by_job结果和jobs的聚合同级
• min_bucket求之前结果的最小值
• 通过bucket_path关键字指定路径

# 平均工资最低的工种
POST employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field": "job.keyword",
        "size": 5
      },
      "aggs": {
        "avg_salary": {
          "avg": {
            "field": "salary"
          }
        }
      }
    },
    "min_salary_by_job":{   
      "min_bucket": {    
        "buckets_path": "jobs>avg_salary"  
      }
    }
  }
}
response
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "jobs" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 2,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "avg_salary" : {
            "value" : 25571.428571428572
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "avg_salary" : {
            "value" : 19250.0
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "avg_salary" : {
            "value" : 21000.0
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 20000.0
          }
        }
      ]
    },
    "min_salary_by_job" : {
      "value" : 19250.0,
      "keys" : [
        "Javascript Programmer"
      ]
    }
  }
}

stats_bucket 示例 平均工资的统计分析

# 平均工资的统计分析
POST employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field": "job.keyword",
        "size": 5
      },
      "aggs": {
        "avg_salary": {
          "avg": {
            "field": "salary"
          }
        }
      }
    },
    "stats_salary_by_job":{
      "stats_bucket": {
        "buckets_path": "jobs>avg_salary"
      }
    }
  }
}
response
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "jobs" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 2,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "avg_salary" : {
            "value" : 25571.428571428572
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "avg_salary" : {
            "value" : 19250.0
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "avg_salary" : {
            "value" : 21000.0
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 20000.0
          }
        }
      ]
    },
    "stats_salary_by_job" : {
      "count" : 5,
      "min" : 19250.0,
      "max" : 25571.428571428572,
      "avg" : 22164.285714285717,
      "sum" : 110821.42857142858
    }
  }
}

percentiles_bucket示例 平均工资的百分位数

# 平均工资的百分位数
POST employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field": "job.keyword",
        "size": 5
      },
      "aggs": {
        "avg_salary": {
          "avg": {
            "field": "salary"
          }
        }
      }
    },
    "percentiles_salary_by_job":{
      "percentiles_bucket": {
        "buckets_path": "jobs>avg_salary"
      }
    }
  }
}
response
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "jobs" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 2,
      "buckets" : [
        {
          "key" : "Java Programmer",
          "doc_count" : 7,
          "avg_salary" : {
            "value" : 25571.428571428572
          }
        },
        {
          "key" : "Javascript Programmer",
          "doc_count" : 4,
          "avg_salary" : {
            "value" : 19250.0
          }
        },
        {
          "key" : "QA",
          "doc_count" : 3,
          "avg_salary" : {
            "value" : 21000.0
          }
        },
        {
          "key" : "DBA",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : "Web Designer",
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 20000.0
          }
        }
      ]
    },
    "percentiles_salary_by_job" : {
      "values" : {
        "1.0" : 19250.0,
        "5.0" : 19250.0,
        "25.0" : 20000.0,
        "50.0" : 21000.0,
        "75.0" : 25000.0,
        "95.0" : 25571.428571428572,
        "99.0" : 25571.428571428572
      }
    }
  }
}

cumulative_sum 实例

#cumulative_sum   累计求和
POST employees/_search
{
  "size": 0,
  "aggs": {
    "age": {
      "histogram": {
        "field": "age",
        "min_doc_count": 0,
        "interval": 1
      },
      "aggs": {
        "avg_salary": {
          "avg": {
            "field": "salary"
          }
        },
        "cumulative_salary":{
          "cumulative_sum": {
            "buckets_path": "avg_salary"
          }
        }
      }
    }
  }
}

response
{
  "took" : 2,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 20,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "age" : {
      "buckets" : [
        {
          "key" : 20.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 9000.0
          },
          "cumulative_salary" : {
            "value" : 9000.0
          }
        },
        {
          "key" : 21.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 16000.0
          },
          "cumulative_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : 22.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : 23.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : 24.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 25000.0
          }
        },
        {
          "key" : 25.0,
          "doc_count" : 3,
          "avg_salary" : {
            "value" : 17333.333333333332
          },
          "cumulative_salary" : {
            "value" : 42333.33333333333
          }
        },
        {
          "key" : 26.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 22000.0
          },
          "cumulative_salary" : {
            "value" : 64333.33333333333
          }
        },
        {
          "key" : 27.0,
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 20000.0
          },
          "cumulative_salary" : {
            "value" : 84333.33333333333
          }
        },
        {
          "key" : 28.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 84333.33333333333
          }
        },
        {
          "key" : 29.0,
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 20000.0
          },
          "cumulative_salary" : {
            "value" : 104333.33333333333
          }
        },
        {
          "key" : 30.0,
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 30000.0
          },
          "cumulative_salary" : {
            "value" : 134333.3333333333
          }
        },
        {
          "key" : 31.0,
          "doc_count" : 2,
          "avg_salary" : {
            "value" : 28500.0
          },
          "cumulative_salary" : {
            "value" : 162833.3333333333
          }
        },
        {
          "key" : 32.0,
          "doc_count" : 3,
          "avg_salary" : {
            "value" : 27333.333333333332
          },
          "cumulative_salary" : {
            "value" : 190166.66666666666
          }
        },
        {
          "key" : 33.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 28000.0
          },
          "cumulative_salary" : {
            "value" : 218166.66666666666
          }
        },
        {
          "key" : 34.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 218166.66666666666
          }
        },
        {
          "key" : 35.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 218166.66666666666
          }
        },
        {
          "key" : 36.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 38000.0
          },
          "cumulative_salary" : {
            "value" : 256166.66666666666
          }
        },
        {
          "key" : 37.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 256166.66666666666
          }
        },
        {
          "key" : 38.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 256166.66666666666
          }
        },
        {
          "key" : 39.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 256166.66666666666
          }
        },
        {
          "key" : 40.0,
          "doc_count" : 0,
          "avg_salary" : {
            "value" : null
          },
          "cumulative_salary" : {
            "value" : 256166.66666666666
          }
        },
        {
          "key" : 41.0,
          "doc_count" : 1,
          "avg_salary" : {
            "value" : 50000.0
          },
          "cumulative_salary" : {
            "value" : 306166.6666666666
          }
        }
      ]
    }
  }
}

聚合的作用范围 query、filter、post_filter、global

ES聚合分析的默认作用范围是query的查询结果集，同时ES还支持以下方式改变聚合的作用范围：

• Filter
• Post Filter
• Global

#Query
POST employees/_search
{
  "size": 0,
  "query": {
    "range": {
      "age": {
        "gte": 20
      }
    }
  },
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword"
        
      }
    }
  }
}

#Filter
POST employees/_search
{
  "size": 0,
  "aggs": {
    "older_person": {
      "filter":{
        "range":{
          "age":{
            "from":35
          }
        }
      },
      "aggs":{
         "jobs":{
           "terms": {
        "field":"job.keyword"
      }
      }
    }},
    "all_jobs": {
      "terms": {
        "field":"job.keyword
      }
    }
  }
}



#Post field. 一条语句，找出所有的job类型。还能找到聚合后符合条件的结果
POST employees/_search
{
  "aggs": {
    "jobs": {
      "terms": {
        "field": "job.keyword"
      }
    }
  },
  "post_filter": {
    "match": {
      "job.keyword": "Dev Manager"
    }
  }
}


#global 
POST employees/_search
{
  "size": 0,
  "query": {
    "range": {
      "age": {
        "gte": 40
      }
    }
  },
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword"
        
      }
    },
    
    "all":{
      "global":{},
      "aggs":{
        "salary_avg":{
          "avg":{
            "field":"salary"
          }
        }
      }
    }
  }
}

排序

指定order，按照count和key进行排序：

• 默认情况，按照count降序排序
• 指定size，就能返回相应的桶

#排序 order
#count and key
POST employees/_search
{
  "size": 0,
  "query": {
    "range": {
      "age": {
        "gte": 20
      }
    }
  },
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword",
        "order":[
          {"_count":"asc"},
          {"_key":"desc"}
          ]
        
      }
    }
  }
}


#排序 order
#count and key
POST employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword",
        "order":[  {
            "avg_salary":"desc"
          }]
        
        
      },
    "aggs": {
      "avg_salary": {
        "avg": {
          "field":"salary"
        }
      }
    }
    }
  }
}


#排序 order
#count and key
POST employees/_search
{
  "size": 0,
  "aggs": {
    "jobs": {
      "terms": {
        "field":"job.keyword",
        "order":[  {
            "stats_salary.min":"desc"
          }]
        
        
      },
    "aggs": {
      "stats_salary": {
        "stats": {
          "field":"salary"
        }
      }
    }
    }
  }
}

Elasticsearch 聚合性能优化

1. ES聚合分析不精准原因分析

ElasticSearch在对海量数据进行聚合分析的时候会损失搜索的精准度来满足实时性的需求
在这里插入图片描述

不精准的原因： 数据分散到多个分片，聚合是每个分片的取 Top X，导致结果不精准。ES 可以不每个分片Top X，而是全量聚合，但势必这会有很大的性能问题。

思考：如何提高聚合精确度？

方案1：设置主分片为1

注意7.x版本已经默认为1

适用场景：数据量小的小集群规模业务场景

方案2：调大 shard_size 值 官方推荐：size*1.5+10

设置 shard_size 为比较大的值，官方推荐：size*1.5+10。shard_size 值越大，结果越趋近于精准聚合结果值。此外，还可以通过show_term_doc_count_error参数显示最差情况下的错误值，用于辅助确定 shard_size 大小。

• size：是聚合结果的返回值，客户期望返回聚合排名前三，size值就是 3。
• shard_size: 每个分片上聚合的数据条数。shard_size 原则上要大于等于 size

适用场景：数据量大、分片数多的集群业务场景

测试： 使用kibana的测试数据

在Terms Aggregation的返回中有两个特殊的数值：

• doc_count_error_upper_bound : 被遗漏的term 分桶，包含的文档，有可能的最大值
• sum_other_doc_count: 除了返回结果 bucket的terms以外，其他 terms 的文档总数（总数-返回的总数)

DELETE my_flights
PUT my_flights
{
  "settings": {
    "number_of_shards": 20
  },
  "mappings" : {
      "properties" : {
        "AvgTicketPrice" : {
          "type" : "float"
        },
        "Cancelled" : {
          "type" : "boolean"
        },
        "Carrier" : {
          "type" : "keyword"
        },
        "Dest" : {
          "type" : "keyword"
        },
        "DestAirportID" : {
          "type" : "keyword"
        },
        "DestCityName" : {
          "type" : "keyword"
        },
        "DestCountry" : {
          "type" : "keyword"
        },
        "DestLocation" : {
          "type" : "geo_point"
        },
        "DestRegion" : {
          "type" : "keyword"
        },
        "DestWeather" : {
          "type" : "keyword"
        },
        "DistanceKilometers" : {
          "type" : "float"
        },
        "DistanceMiles" : {
          "type" : "float"
        },
        "FlightDelay" : {
          "type" : "boolean"
        },
        "FlightDelayMin" : {
          "type" : "integer"
        },
        "FlightDelayType" : {
          "type" : "keyword"
        },
        "FlightNum" : {
          "type" : "keyword"
        },
        "FlightTimeHour" : {
          "type" : "keyword"
        },
        "FlightTimeMin" : {
          "type" : "float"
        },
        "Origin" : {
          "type" : "keyword"
        },
        "OriginAirportID" : {
          "type" : "keyword"
        },
        "OriginCityName" : {
          "type" : "keyword"
        },
        "OriginCountry" : {
          "type" : "keyword"
        },
        "OriginLocation" : {
          "type" : "geo_point"
        },
        "OriginRegion" : {
          "type" : "keyword"
        },
        "OriginWeather" : {
          "type" : "keyword"
        },
        "dayOfWeek" : {
          "type" : "integer"
        },
        "timestamp" : {
          "type" : "date"
        }
      }
    }
}

POST _reindex
{
  "source": {
    "index": "kibana_sample_data_flights"
  },
  "dest": {
    "index": "my_flights"
  }
}

GET my_flights/_count
GET kibana_sample_data_flights/_search
{
  "size": 0,
  "aggs": {
    "weather": {
      "terms": {
        "field":"OriginWeather",
        "size":5,
        "show_term_doc_count_error":true
      }
    }
  }
}

GET my_flights/_search
{
  "size": 0,
  "aggs": {
    "weather": {
      "terms": {
        "field":"OriginWeather",
        "size":5,
        "shard_size":10,
        "show_term_doc_count_error":true
      }
    }
  }
}

方案3：将size设置为全量值，来解决精度问题

将size设置为2的32次方减去1也就是分片支持的最大值，来解决精度问题。
原因：1.x版本，size等于 0 代表全部，高版本取消 0 值，所以设置了最大值（大于业务的全量值）。

全量带来的弊端就是：如果分片数据量极大，这样做会耗费巨大的CPU 资源来排序，而且可能会阻塞网络。

适用场景：对聚合精准度要求极高的业务场景，由于性能问题，不推荐使用。

方案4：使用Clickhouse/ Spark 进行精准聚合

适用场景：数据量非常大、聚合精度要求高、响应速度快的业务场景。

2. 启用 eager global ordinals 提升高基数聚合性能 ---- 以空间换时间

适用场景：高基数聚合 。高基数聚合场景中的高基数含义：一个字段包含很大比例的唯一值。

global ordinals 中文翻译成全局序号，是一种数据结构，应用场景如下：

• 基于 keyword，ip 等字段的分桶聚合，包含：terms聚合、composite 聚合等。
• 基于text 字段的分桶聚合（前提条件是：fielddata 开启）。
• 基于父子文档 Join 类型的 has_child 查询和 父聚合。

global ordinals 使用一个数值代表字段中的字符串值，然后为每一个数值分配一个 bucket（分桶）。

global ordinals 的本质是：启用 eager_global_ordinals 时，会在刷新（refresh）分片时构建全局序号。这将构建全局序号的成本从搜索阶段转移到了数据索引化（写入）阶段。

创建索引的同时开启：eager_global_ordinals

PUT /my-index
{
  "mappings": {
    "properties": {
      "tags": {
        "type": "keyword",
        "eager_global_ordinals": true
      }
    }
  }

注意：开启 eager_global_ordinals 会影响写入性能，因为每次刷新时都会创建新的全局序号。为了最大程度地减少由于频繁刷新建立全局序号而导致的额外开销，请调大刷新间隔 refresh_interval

PUT my-index/_settings
{
  "index": {
    "refresh_interval": "30s"
  }

3. 插入数据时对索引进行预排序

Index sorting （索引排序）可用于在插入时对索引进行预排序，而不是在查询时再对索引进行排序，这将提高范围查询（range query）和排序操作的性能。
在 Elasticsearch 中创建新索引时，可以配置如何对每个分片内的段进行排序。
这是 Elasticsearch 6.X 之后版本才有的特性。

PUT /my_index
{
  "settings": {
    "index":{
      "sort.field": "create_time",
      "sort.order": "desc"
    }
  },
  "mappings": {
    "properties": {
      "create_time":{
        "type": "date"
      }
    }
  }
}

注意：预排序将增加 Elasticsearch 写入的成本。在某些用户特定场景下，开启索引预排序会导致大约 40%-50% 的写性能下降。也就是说，如果用户场景更关注写性能的业务，开启索引预排序不是一个很好的选择。

4. 使用节点查询缓存

节点查询缓存（Node query cache）可用于有效缓存过滤器（filter）操作的结果。如果多次执行同一 filter 操作，这将很有效，但是即便更改过滤器中的某一个值，也将意味着需要计算新的过滤器结果。
例如，由于 “now” 值一直在变化，因此无法缓存在过滤器上下文中使用 “now” 的查询。
那怎么使用缓存呢？通过在 now 字段上应用 datemath 格式将其四舍五入到最接近的分钟/小时等，可以使此类请求更具可缓存性，以便可以对筛选结果进行缓存。

PUT /my_index/_doc/1
{
  "create_time":"2022-05-11T16:30:55.328Z"
}

#下面的示例无法使用缓存
GET /my_index/_search
{
  "query":{
    "constant_score": {
      "filter": {
        "range": {
          "create_time": {
            "gte": "now-1h",
            "lte": "now"
          }
        }
      }
    }
  }
}

# 下面的示例就可以使用节点查询缓存。
GET /my_index/_search
{
  "query":{
    "constant_score": {
      "filter": {
        "range": {
          "create_time": {
            "gte": "now-1h/m",
            "lte": "now/m"
          }
        }
      }
    }
  }
}

上述示例中的“now-1h/m” 就是 datemath 的格式。
如果当前时间 now 是：16:31:29，那么range query 将匹配 my_date 介于：15:31:00 和 15:31:59 之间的时间数据。同理，聚合的前半部分 query 中如果有基于时间查询，或者后半部分 aggs 部分中有基于时间聚合的，建议都使用 datemath 方式做缓存处理以优化性能

5. 使用分片请求缓存

聚合语句中，设置：size：0，就会使用分片请求缓存缓存结果。size = 0 的含义是：只返回聚合结果，不返回查询结果。

GET /es_db/_search
{
  "size": 0,
  "aggs": {
    "remark_agg": {
      "terms": {
        "field": "remark.keyword"
      }
    }
  }
}

6. 拆分聚合，使聚合并行化

Elasticsearch 查询条件中同时有多个条件聚合，默认情况下聚合不是并行运行的。当为每个聚合提供自己的查询并执行 msearch 时，性能会有显著提升。因此，在 CPU 资源不是瓶颈的前提下，如果想缩短响应时间，可以将多个聚合拆分为多个查询，借助：msearch 实现并行聚合。

#常规的多条件聚合实现
GET /employees/_search
{
  "size": 0,
  "aggs": {
    "job_agg": {
      "terms": {
        "field": "job.keyword"
      }
    },
    "max_salary":{
      "max": {
        "field": "salary"
      }
    }
  }
}
# msearch 拆分多个语句的聚合实现
GET _msearch
{"index":"employees"}
{"size":0,"aggs":{"job_agg":{"terms":{"field": "job.keyword"}}}}
{"index":"employees"}
{"size":0,"aggs":{"max_salary":{"max":{"field": "salary"}}}}

init data

DELETE /employees
#创建索引库
PUT /employees
{
  "mappings": {
    "properties": {
      "age":{
        "type": "integer"
      },
      "gender":{
        "type": "keyword"
      },
      "job":{
         "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 50
            }
          }
      },
      "name":{
        "type": "keyword"
      },
      "salary":{
        "type": "integer"
      }
    }
  }
}

PUT /employees/_bulk
{ "index" : {  "_id" : "1" } }
{ "name" : "Emma","age":32,"job":"Product Manager","gender":"female","salary":35000 }
{ "index" : {  "_id" : "2" } }
{ "name" : "Underwood","age":41,"job":"Dev Manager","gender":"male","salary": 50000}
{ "index" : {  "_id" : "3" } }
{ "name" : "Tran","age":25,"job":"Web Designer","gender":"male","salary":18000 }
{ "index" : {  "_id" : "4" } }
{ "name" : "Rivera","age":26,"job":"Web Designer","gender":"female","salary": 22000}
{ "index" : {  "_id" : "5" } }
{ "name" : "Rose","age":25,"job":"QA","gender":"female","salary":18000 }
{ "index" : {  "_id" : "6" } }
{ "name" : "Lucy","age":31,"job":"QA","gender":"female","salary": 25000}
{ "index" : {  "_id" : "7" } }
{ "name" : "Byrd","age":27,"job":"QA","gender":"male","salary":20000 }
{ "index" : {  "_id" : "8" } }
{ "name" : "Foster","age":27,"job":"Java Programmer","gender":"male","salary": 20000}
{ "index" : {  "_id" : "9" } }
{ "name" : "Gregory","age":32,"job":"Java Programmer","gender":"male","salary":22000 }
{ "index" : {  "_id" : "10" } }
{ "name" : "Bryant","age":20,"job":"Java Programmer","gender":"male","salary": 9000}
{ "index" : {  "_id" : "11" } }
{ "name" : "Jenny","age":36,"job":"Java Programmer","gender":"female","salary":38000 }
{ "index" : {  "_id" : "12" } }
{ "name" : "Mcdonald","age":31,"job":"Java Programmer","gender":"male","salary": 32000}
{ "index" : {  "_id" : "13" } }
{ "name" : "Jonthna","age":30,"job":"Java Programmer","gender":"female","salary":30000 }
{ "index" : {  "_id" : "14" } }
{ "name" : "Marshall","age":32,"job":"Javascript Programmer","gender":"male","salary": 25000}
{ "index" : {  "_id" : "15" } }
{ "name" : "King","age":33,"job":"Java Programmer","gender":"male","salary":28000 }
{ "index" : {  "_id" : "16" } }
{ "name" : "Mccarthy","age":21,"job":"Javascript Programmer","gender":"male","salary": 16000}
{ "index" : {  "_id" : "17" } }
{ "name" : "Goodwin","age":25,"job":"Javascript Programmer","gender":"male","salary": 16000}
{ "index" : {  "_id" : "18" } }
{ "name" : "Catherine","age":29,"job":"Javascript Programmer","gender":"female","salary": 20000}
{ "index" : {  "_id" : "19" } }
{ "name" : "Boone","age":30,"job":"DBA","gender":"male","salary": 30000}
{ "index" : {  "_id" : "20" } }
{ "name" : "Kathy","age":29,"job":"DBA","gender":"female","salary": 20000}