Elasticsearch高手进阶篇(15)
深度探秘搜索技术_使用most_fields策略进行cross-fields search弊端大揭秘
cross-fields搜索
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cross-fields搜索,一个唯一标识,跨了多个field。比如一个人,标识,是姓名;一个建筑,它的标识是地址。姓名可以散落在多个field中,比如first_name和last_name中,地址可以散落在country,province,city中。
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跨多个field搜索一个标识,比如搜索一个人名,或者一个地址,就是cross-fields搜索
初步来说,如果要实现,可能用most_fields比较合适。因为best_fields是优先搜索单个field最匹配的结果,cross-fields本身就不是一个field的问题了。
POST /waws/article/_bulk
{ "update": { "_id": "1"}}
{ "doc" : {"author_first_name" : "Peter", "author_last_name" : "Smith"}}
{ "update": { "_id": "2"}}
{ "doc" : {"author_first_name" : "Smith", "author_last_name" : "Williams"}}
{ "update": { "_id": "3"}}
{ "doc" : {"author_first_name" : "Jack", "author_last_name" : "Ma"}}
{ "update": { "_id": "4"}}
{ "doc" : {"author_first_name" : "Robbin", "author_last_name" : "Li"}}
{ "update": { "_id": "5"}}
{ "doc" : {"author_first_name" : "Tonny", "author_last_name" : "Peter Smith"}}
- 搜索数据
GET /waws/article/_search
{
"query": {
"multi_match": {
"query":"Peter Smith",
"type":"most_fields",
"fields":[ "author_first_name", "author_last_name" ]
}
}
}
# Peter Smith,匹配author_first_name,匹配到了Smith,这时候它的分数很高,为什么啊???
# 因为IDF分数高,IDF分数要高,那么这个匹配到的term(Smith),在所有doc中的出现频率要低,author_first_name field中,Smith就出现过1次
# Peter Smith这个人,doc 1,Smith在author_last_name中,但是author_last_name出现了两次Smith,所以导致doc 1的IDF分数较低
{
"took": 1,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 3,
"max_score": 0.6931472,
"hits": [
{
"_index": "waws",
"_type": "article",
"_id": "2",
"_score": 0.6931472,
"_source": {
"articleID": "KDKE-B-9947-#kL5",
"userID": 1,
"hidden": false,
"postDate": "2017-01-02",
"tag": [
"java"
],
"tag_cnt": 1,
"view_cnt": 50,
"title": "this is java blog",
"content": "i think java is the best programming language",
"sub_title": "learned a lot of course",
"author_first_name": "Smith",
"author_last_name": "Williams"
}
},
{
"_index": "waws",
"_type": "article",
"_id": "1",
"_score": 0.5753642,
"_source": {
"articleID": "XHDK-A-1293-#fJ3",
"userID": 1,
"hidden": false,
"postDate": "2017-01-01",
"tag": [
"java",
"hadoop"
],
"tag_cnt": 2,
"view_cnt": 30,
"title": "this is java and elasticsearch blog",
"content": "i like to write best elasticsearch article",
"sub_title": "learning more courses",
"author_first_name": "Peter",
"author_last_name": "Smith"
}
},
{
"_index": "waws",
"_type": "article",
"_id": "5",
"_score": 0.51623213,
"_source": {
"articleID": "DHJK-B-1395-#Ky5",
"userID": 3,
"hidden": false,
"postDate": "2017-03-01",
"tag": [
"elasticsearch"
],
"tag_cnt": 1,
"view_cnt": 10,
"title": "this is spark blog",
"content": "spark is best big data solution based on scala ,an programming language similar to java",
"sub_title": "haha, hello world",
"author_first_name": "Tonny",
"author_last_name": "Peter Smith"
}
}
]
}
}
问题1:只是找到尽可能多的field匹配的doc,而不是某个field完全匹配的doc
问题2:most_fields,没办法用minimum_should_match去掉长尾数据,就是匹配的特别少的结果
问题3:TF/IDF算法,比如Peter Smith和Smith Williams,搜索Peter Smith的时候,由于first_name中很少有Smith的,所以query在所有document中的频率很低,得到的分数很高,可能Smith Williams反而会排在Peter Smith前面
Elasticsearch高手进阶篇(16)
深度探秘搜索技术_使用copy_to定制组合field解决cross-fields搜索弊端
上一讲,我们其实说了,用most_fields策略,去实现cross-fields搜索,有3大弊端,而且搜索结果也显示出了这3大弊端
- 第一个办法:用copy_to,将多个field组合成一个field
问题其实就出在有多个field,有多个field以后,就很尴尬,我们只要想办法将一个标识跨在多个field的情况,合并成一个field即可。比如说,一个人名,本来是first_name,last_name,现在合并成一个full_name,不就ok了吗
PUT /waws/_mapping/article
{
"properties": {
"new_author_first_name": {
"type":"string",
"copy_to":"new_author_full_name"
},
"new_author_last_name": {
"type":"string",
"copy_to":"new_author_full_name"
},
"new_author_full_name": {
"type":"string"
}
}
}
用了这个copy_to语法之后,就可以将多个字段的值拷贝到一个字段中,并建立倒排索引
POST /waws/article/_bulk
{ "update": { "_id": "1"}}
{ "doc" : {"new_author_first_name" : "Peter", "new_author_last_name" : "Smith"}}
{ "update": { "_id": "2"}}
{ "doc" : {"new_author_first_name" : "Smith", "new_author_last_name" : "Williams"}}
{ "update": { "_id": "3"}}
{ "doc" : {"new_author_first_name" : "Jack", "new_author_last_name" : "Ma"}}
{ "update": { "_id": "4"}}
{ "doc" : {"new_author_first_name" : "Robbin", "new_author_last_name" : "Li"}}
{ "update": { "_id": "5"}}
{ "doc" : {"new_author_first_name" : "Tonny", "new_author_last_name" : "Peter Smith"}}
- 搜索数据
GET /waws/article/_search
{
"query": {
"match": {
"new_author_full_name":"Peter Smith"
}
}
}
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 3,
"max_score": 0.62191015,
"hits": [
{
"_index": "waws",
"_type": "article",
"_id": "2",
"_score": 0.62191015,
"_source": {
"articleID": "KDKE-B-9947-#kL5",
"userID": 1,
"hidden": false,
"postDate": "2017-01-02",
"tag": [
"java"
],
"tag_cnt": 1,
"view_cnt": 50,
"title": "this is java blog",
"content": "i think java is the best programming language",
"sub_title": "learned a lot of course",
"author_first_name": "Smith",
"author_last_name": "Williams",
"new_author_last_name": "Williams",
"new_author_first_name": "Smith"
}
},
{
"_index": "waws",
"_type": "article",
"_id": "1",
"_score": 0.51623213,
"_source": {
"articleID": "XHDK-A-1293-#fJ3",
"userID": 1,
"hidden": false,
"postDate": "2017-01-01",
"tag": [
"java",
"hadoop"
],
"tag_cnt": 2,
"view_cnt": 30,
"title": "this is java and elasticsearch blog",
"content": "i like to write best elasticsearch article",
"sub_title": "learning more courses",
"author_first_name": "Peter",
"author_last_name": "Smith",
"new_author_last_name": "Smith",
"new_author_first_name": "Peter"
}
},
{
"_index": "waws",
"_type": "article",
"_id": "5",
"_score": 0.5063205,
"_source": {
"articleID": "DHJK-B-1395-#Ky5",
"userID": 3,
"hidden": false,
"postDate": "2017-03-01",
"tag": [
"elasticsearch"
],
"tag_cnt": 1,
"view_cnt": 10,
"title": "this is spark blog",
"content": "spark is best big data solution based on scala ,an programming language similar to java",
"sub_title": "haha, hello world",
"author_first_name": "Tonny",
"author_last_name": "Peter Smith",
"new_author_last_name": "Peter Smith",
"new_author_first_name": "Tonny"
}
}
]
}
}
效果难以复现。比如官网也会给一些例子,说用什么什么文本,怎么怎么搜索,是怎么怎么样的效果。es版本在不断迭代,这个打分的算法也在不断的迭代。所以我们其实很难说,对类似这几讲讲解的best_fields,most_fields,cross_fields,完全复现出来应有的场景和效果。
期望的是说,比如大家自己在开发搜索应用的时候,碰到需要best_fields的场景,知道怎么做,知道best_fields的原理,可以达到什么效果;碰到most_fields的场景,知道怎么做,以及原理;碰到搜搜cross_fields标识的场景,知道怎么做,知道原理是什么,效果是什么
- 问题的解决
问题1:只是找到尽可能多的field匹配的doc,而不是某个field完全匹配的doc --> 解决,最匹配的document被最先返回
问题2:most_fields,没办法用minimum_should_match去掉长尾数据,就是匹配的特别少的结果 --> 解决,可以使用minimum_should_match去掉长尾数据
问题3:TF/IDF算法,比如Peter Smith和Smith Williams,搜索Peter Smith的时候,由于first_name中很少有Smith的,所以query在所有document中的频率很低,得到的分数很高,可能Smith Williams反而会排在Peter Smith前面 --> 解决,Smith和Peter在一个field了,所以在所有document中出现的次数是均匀的,不会有极端的偏差