Elasticsearch 推荐器suggester

Myth丶恋晨 2023-01-01 10:58 165阅读 0赞

Elasticsearch使用推荐器，给用户的输入推荐相似的内容，其实现原理是：把用户输入的文本转换成token,去索引中查询相似的term进行返回。推荐器模式有三种：missing 当搜索不到时候进行推荐；popular 推荐相似的且出现频率最高的文档中的词；always 总是推荐。推荐器有 term推荐器、phrase推荐器和completion推荐器等，term推荐器：根据输入的term推荐相似的term,默认首字母不匹配不推荐，可以设置prefix\_length进行推荐；phrase推荐器：根据输入的phrase推荐相似的phrase，可以设置最大允许出错的词的数量；completion推荐器，进行自动补全，根据用户输入的字符，按前缀进行匹配推荐，它没有使用倒排索引，而是使用一种特殊的数据结构，对analyze数据进行编码，全部加载到内存，性能非常高。在使用completion推荐器时候，需要在mapping中设置字段类型为completion，如果想提升搜索的精准性，可以在mapping的context中指定一个分类类型，在进行索引和搜索时候使用这个类型提升精准性。

三种推荐器比较：

精准性：

completion > phrase > term

召回率：

term > phrase > completion

性能：

completion > phrase >term

初始化数据
    DELETE articles
    POST articles/_bulk
    { "index" : { } }
    { "body": "lucene is very cool"}
    { "index" : { } }
    { "body": "Elasticsearch builds on top of lucene"}
    { "index" : { } }
    { "body": "Elasticsearch rocks"}
    { "index" : { } }
    { "body": "elastic is the company behind ELK stack "}
    { "index" : { } }
    { "body": "Elk stack rocks"}
    { "index" : {} }
    {  "body": "elasticsearch is rock solid"}
    
    term 推荐器，类型为只有不存在才推荐，lucen 推荐 lucene，rock没有推荐
    post articles/_search
    {
      "size":1,
      "query":{
        "match": {
          "body": "lucen rock"
        }
      },
      "suggest":{
        "term-suggestion":{
          "text":"lucen rock",
          "term":{
            "suggest_mode":"missing",
            "field":"body"
          }
        }
      }
    }
    
    term 推荐器类型设置为popular,rock也给出了推荐出文档出现最多的rocks
    post articles/_search
    {
      "suggest":{
        "term-suggestion":{
          "text":"lucen rock",
          "term":{
            "suggest_mode":"popular",
            "field":"body"
          }
        }
      }
    }
    
    term 推荐器 类型设置为always 无论是否存在都推荐
    post articles/_search
    {
      "suggest":{
        "term-suggestion":{
          "text":"lucen rock",
          "term":{
            "suggest_mode":"always",
            "field":"body"
          }
        }
      }
    }
    
    和上面一致，查询hocks 默认首字母不一致不把hocks推荐为rocks 没有被推荐为rocks
    post articles/_search
    {
      "suggest":{
        "term-suggestion":{
          "text":"lucen hocks",
          "term":{
            "suggest_mode":"always",
            "field":"body"
          }
        }
      }
    }
    
    和上面一致 查询hocks出现了推荐，prefix_length 首字母不匹配也会推荐，当有多个推荐词时默认是按acore排序，指定sort 会按推荐词的频率排序
    post articles/_search
    {
      "suggest":{
        "term-suggestion":{
          "text":"lucen hocks",
          "term":{
            "suggest_mode":"always",
            "field":"body",
            "prefix_length":0,
            "sort":"frequency"
          }
        }
      }
    }
    
    phrase 推荐器，最多允许2个词错误，confidence影响返回数量，值越大返回越少
    post articles/_search
    {
      "suggest":{
        "my-suggestion":{
          "text":"lucne and elasticsear rock hello world",
          "phrase":{
            "field":"body",
            "max_errors":2,
            "confidence":2,
            "direct_generator":[{
              "suggest_mode":"always",
              "field":"body"
            }],
            "highlight":{
              "pre_tag": "<em>",
              "post_tag": "</em>" 
            }
          }
        }
      }
    }

completion推荐器，进行自动补全：

设置索引的字段类型为completion
    DELETE articles
    PUT articles
    {
      "mappings": {
        "properties": {
          "title_completion":{
            "type": "completion"
          }
        }
      }
    }
    
    初始化数据
    POST articles/_bulk
    { "index" : { } }
    { "title_completion": "lucene is very cool"}
    { "index" : { } }
    { "title_completion": "Elasticsearch builds on top of lucene"}
    { "index" : { } }
    { "title_completion": "Elasticsearch rocks"}
    { "index" : { } }
    { "title_completion": "elastic is the company behind ELK stack"}
    { "index" : { } }
    { "title_completion": "Elk stack rocks"}
    { "index" : {} }
    
    前缀为elk 自动补全
    post articles/_search
    {
      "size":0,
      "suggest":{
        "article-suggestr":{
          "prefix":"elk",
          "completion":{
            "field":"title_completion"
          }
        }
      }
    }
    
    给字段comment_autocomplete 指定类型为自动补全 并添加上下文类型
    delete comments
    put comments
    put comments/_mapping
    {
      "properties":{
        "comment_autocomplete":{
          "type":"completion",
          "contexts":[{
              "type":"category",
              "name":"comment_category"
            }]
        }
      }
    }
    
    初始化数据 指定上下文类型为movies
    POST comments/_doc
    {
      "comment":"I love the star war movies",
      "comment_autocomplete":{
        "input":["star wars"],
        "contexts":{
          "comment_category":"movies"
        }
      }
    }
    初始化数据 指定上下文类型为coffee
    POST comments/_doc
    {
      "comment":"Where can I find a Starbucks",
      "comment_autocomplete":{
        "input":["starbucks"],
        "contexts":{
          "comment_category":"coffee"
        }
      }
    }
    
    按前缀自动补全 指定类型为coffee
    post comments/_search
    {
      "suggest":{
        "my-suggestion":{
          "prefix":"sta",
          "completion":{
            "field":"comment_autocomplete",
            "contexts":{
              "comment_category":"coffee"
            }
          }
        }
      }
    }