Elasticsearch 6.8 match_phrase搜索N元语法分词器效果不佳

问题描述

我使用Elasticsearch N-gram tokenizer并使用match_phrase进行模糊匹配 我的索引和测试数据如下：

DELETE /m8
PUT m8
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "my_tokenizer"
        }
      },"tokenizer": {
        "my_tokenizer": {
          "type": "ngram","min_gram": 1,"max_gram": 3,"custom_token_chars":"_."
        }
      }
    },"max_ngram_diff": 10
  },"mappings": {
    "table": {
      "properties": {
        "dataSourceId": {
          "type": "long"
        },"dataSourceType": {
          "type": "integer"
        },"dbname": {
          "type": "text","analyzer": "my_analyzer","fields": {
            "keyword": {
              "type": "keyword","ignore_above": 256
            }
          }
        }
      }
    }
  }
}


PUT /m8/table/1
{
  "dataSourceId":1,"dataSourceType":2,"dbname":"rm.rf"
}

PUT /m8/table/2
{
  "dataSourceId":1,"dbname":"rm_rf"
}
PUT /m8/table/3
{
  "dataSourceId":1,"dbname":"rmrf"
}

检查_analyze：

POST m8/_analyze
{
  "tokenizer": "my_tokenizer","text": "rm.rf"
}

_analyze结果：

{
  "tokens" : [
    {
      "token" : "r","start_offset" : 0,"end_offset" : 1,"type" : "word","position" : 0
    },{
      "token" : "rm","end_offset" : 2,"position" : 1
    },{
      "token" : "rm.","end_offset" : 3,"position" : 2
    },{
      "token" : "m","start_offset" : 1,"position" : 3
    },{
      "token" : "m.","position" : 4
    },{
      "token" : "m.r","end_offset" : 4,"position" : 5
    },{
      "token" : ".","start_offset" : 2,"position" : 6
    },{
      "token" : ".r","position" : 7
    },{
      "token" : ".rf","end_offset" : 5,"position" : 8
    },{
      "token" : "r","start_offset" : 3,"position" : 9
    },{
      "token" : "rf","position" : 10
    },{
      "token" : "f","start_offset" : 4,"position" : 11
    }
  ]
}

当我搜索“ rm”时，什么也没找到：

GET /m8/table/_search
{
  "query": {
    "bool": {
      "must": [
        {
          "match_phrase": {
            "dbname": "rm"
          }
        }
      ]
    }
  }
}

{
  "took" : 2,"timed_out" : false,"_shards" : {
    "total" : 5,"successful" : 5,"skipped" : 0,"Failed" : 0
  },"hits" : {
    "total" : 0,"max_score" : null,"hits" : [ ]
  }
}

但是可以找到'.rf'：

{
  "took" : 1,"hits" : {
    "total" : 1,"max_score" : 1.7260926,"hits" : [
      {
        "_index" : "m8","_type" : "table","_id" : "1","_score" : 1.7260926,"_source" : {
          "dataSourceId" : 1,"dataSourceType" : 2,"dbname" : "rm.rf"
        }
      }
    ]
  }
}

我的问题： 为什么即使_analyze拆分了这些短语也找不到“ rm”？

解决方法

1. my_analyzer也将在搜索期间使用。

   "mapping":{
    "dbName": {
     "type": "text","analyzer": "my_analyzer" 
     "search_analyzer":"my_analyzer"  // <==== If you don't provide a search analyzer then what you defined in analyzer will be used during search time as well.
   

2. Match_phrase查询用于考虑已分析文本的位置来匹配短语。例如，搜索“ Kal ho”将匹配分析文本中X位置具有“ Kal”和X + 1位置具有“ ho”的文档。

3. 当您搜索“ rm”（＃1）时，将使用my_analyzer分析文本，该文本将其转换为n-gram，并将在该phrase_search的顶部使用。因此，结果是无法预期的。

解决方案：

1. 使用带有简单匹配查询的标准分析器

   GET /m8/_search
   {
    "query": {
    "bool": {
      "must": [
        {
          "match": {
            "dbName": {
              "query": "rm","analyzer": "standard" // <=========
            }
          }
        }
      ]
    }
    }
    }
   

   或在映射过程中进行定义并使用匹配查询（而非match_phrase）

   "mapping":{
         "dbName": {
          "type": "text","analyzer": "my_analyzer" 
          "search_analyzer":"standard" //<==========
   

后续问题：：为什么要对n-gram令牌生成器使用 match_phrase 查询？