es head 复合查询_【ES进阶】深入理解Elasticsearch检索评分score执行计划及逆向文档词频idf...

GET shopping/_search
{
  "explain": true, 
  "query": {
    "match": {
        "goodsInfoName": "苏泊尔"
    }
  }
}

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 3,
    "successful" : 3,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 24,
      "relation" : "eq"
    },
    "max_score" : 5.3067513,
    "hits" : [
      {
        "_shard" : "[shopping][1]",
        "_node" : "h665-yAdSzGgjxamBh5CjA",
        "_index" : "shopping",
        "_type" : "_doc",
        "_id" : "10976",
        "_score" : 5.3067513,
        "_source" : {
           "goodsInfoName" : "苏泊尔不锈钢压力锅高压锅YS22ED+苏泊尔保鲜盒饭盒便当盒330mlKB033AE1(银色)",
           "其他字段省略....."
        },
        "_explanation" : {
          "value" : 5.3067513,
          "description" : "weight(goodsInfoName:苏泊尔 in 328) [PerFieldSimilarity], result of:",
          "details" : [
            {
              "value" : 5.3067513,
              "description" : "score(freq=2.0), computed as boost * idf * tf from:",
              "details" : [
                {
                  "value" : 2.2,
                  "description" : "boost",
                  "details" : [ ]
                },
                {
                  "value" : 3.6549778,
                  "description" : "idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:",
                  "details" : [
                    {
                      "value" : 10,
                      "description" : "n, number of documents containing term",
                      "details" : [ ]
                    },
                    {
                      "value" : 405,
                      "description" : "N, total number of documents with field",
                      "details" : [ ]
                    }
                  ]
                },
                {
                  "value" : 0.65996563,
                  "description" : "tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:",
                  "details" : [
                    {
                      "value" : 2.0,
                      "description" : "freq, occurrences of term within document",
                      "details" : [ ]
                    },
                    {
                      "value" : 1.2,
                      "description" : "k1, term saturation parameter",
                      "details" : [ ]
                    },
                    {
                      "value" : 0.75,
                      "description" : "b, length normalization parameter",
                      "details" : [ ]
                    },
                    {
                      "value" : 11.0,
                      "description" : "dl, length of field",
                      "details" : [ ]
                    },
                    {
                      "value" : 13.553086,
                      "description" : "avgdl, average length of field",
                      "details" : [ ]
                    }
                  ]
                }
              ]
            }
          ]
        }
      },
      .....略.....

"description" : "score(freq=2.0), computed as boost * idf * tf from:"

在这里，有三个关键词含义分别如下：
boost：查询时候查询项加权值，当前值可以通过创建mapping结构的时候指定，也可以在后期查询的时候动态修改

idf:
反转文档词频，意思是出现的逆词频数，意为查询到的文档记录数和索引中总文档数的一个占比关系，其计算公式如下：
"description" : "idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:"

tf: 词频归一值，即搜索的关键词(未分词或分词后的词组)在被搜索的字段的(未分词或分词后的词组)中所出现的个数对总的分词后的词组数的比例，其计算公式如下：
"description" : "tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:"
在上述DSL语句中，goodsInfoName字段中出现了2次查询关键词"苏泊尔"，而排在第二条记录的当前字段中只出现了1次(两条记录分词词组数量相同)，
所以在tf评分中，第一条记录的评分高于第二条记录，从而影响到整体评分的走向


根据上述执行计划中的三项评分相乘，从而得到文档的最终score评分值
2.2 * 3.6549778 * 0.65996563 = 5.3067513

{
  "value" : 3.6549778,
  "description" : "idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:",
  "details" : [
    {
      "value" : 10,
      "description" : "n, number of documents containing term",
      "details" : [ ]
    },
    {
      "value" : 405,
      "description" : "N, total number of documents with field",
      "details" : [ ]
    }
  ]
}

{
  "value" : 0.65996563,
  "description" : "tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:",
  "details" : [
    {
      "value" : 2.0,
      "description" : "freq, occurrences of term within document",
      "details" : [ ]
    },
    {
      "value" : 1.2,
      "description" : "k1, term saturation parameter",
      "details" : [ ]
    },
    {
      "value" : 0.75,
      "description" : "b, length normalization parameter",
      "details" : [ ]
    },
    {
      "value" : 11.0,
      "description" : "dl, length of field",
      "details" : [ ]
    },
    {
      "value" : 13.553086,
      "description" : "avgdl, average length of field",
      "details" : [ ]
    }
  ]
}