theme: scrolls-light
二次打分
之前文章写的Script Score的搜索打分是针对整个匹配结果集的，如果一个搜索匹配了几十万个文档，对着文档使用过Function Score或者Script Score查询进行打分是非常耗时的，整个排序性能大打折扣。针对这种情况，ElasticSearch提供了Query Score功能作为折中方案，它支持只针对返回文档的一部分文档进行打分。
1.1 二次打分简介
Query Score工作的阶段是在原始查询打分之后，它支持对打分后Top-N的文档集合执行第二次查询和打分。通过设置window_size参数可以控制在每个分片上进行二次打分查询的文档数量，在默认情况下window_size的值为10。在默认情况下，文档的最终得分等于原查询和rescore查询的分数之和。当然，还可以使用参数对这两部分的权重进行控制。
1.2 使用示例
索引结构和数据如下：
PUT /hotel_painless
{
"mappings": {
"properties": {
"title":{
"type": "text"
},
"price":{
"type": "double"
},
"create_time":{
"type": "date"
},
"full_room":{
"type": "boolean"
},
"location":{
"type": "geo_point"
},
"doc_weight":{
"type": "integer"
},
"tags":{
"type": "keyword"
},
"comment_info":{ //定义comment_info字段类型为object
"properties": {
"favourable_comment":{ //定义favourable_comment字段类型为integer
"type":"integer"
},
"negative_comment":{
"type":"integer"
}
}
},
"hotel_vector":{ //定义hotel_vector字段类型为dense_vector
"type": "dense_vector",
"dims":5
}
}
}
}
POST /_bulk
{"index":{"_index":"hotel_painless","_id":"001"}}
{"title":"文雅假日酒店","price":556.00,"create_time":"20200418120000","full_room":false,"location":{"lat":36.083078,"lon":120.37566},"doc_weight":30,"tags":["wifi","小型电影院"],"comment_info":{"favourable_comment":20,"negative_comment":10},"hotel_vector":[0,3.2,5.8,1.2,0]}
{"index":{"_index":"hotel_painless","_id":"002"}}
{"title":"金都嘉怡假日酒店","price":337.00,"create_time":"20210315200000","full_room":false,"location":{"lat":39.915153,"lon":116.4030},"doc_weight":10,"tags":["wifi","免费早餐"],"comment_info":{"favourable_comment":20,"negative_comment":10},"hotel_vector":[0.7,9.2,5.3,1.2,12.3]}
{"index":{"_index":"hotel_painless","_id":"003"}}
{"title":"金都欣欣酒店","price":200.00,"create_time":"20210509160000","full_room":true,"location":{"lat":39.186555,"lon":117.162007},"doc_weight":10,"tags":["会议厅","免费车位"],"comment_info":{"favourable_comment":20,"negative_comment":10},"hotel_vector":[6,3.2,0.4,9.3,0]}
{"index":{"_index":"hotel_painless","_id":"004"}}
{"title":"金都家至酒店","price":500.00,"create_time":"20210218080000","full_room":true,"location":{"lat":39.915343,"lon":116.422011},"doc_weight":50,"tags":["wifi","免费车位"],"comment_info":{"favourable_comment":20,"negative_comment":10},"hotel_vector":[0.7,3.2,5.1,2.9,0.1]}
{"index":{"_index":"hotel_painless","_id":"005"}}
{"title":"文雅精选酒店","price":800.00,"create_time":"20210101080000","full_room":true,"location":{"lat":39.918229,"lon":116.422011},"doc_weight":70,"tags":["wifi","充电车位"],"comment_info":{"favourable_comment":20,"negative_comment":10},"hotel_vector":[12.1,5.2,5.1,9.2,4.5]}
现在有一个比较简单的查询：查询价格大于300元的酒店，DSL如下：
GET /hotel_painless/_search
{
"query": {
"range": {
"price": {
"gte": 300
}
}
}
}
从结果中可看出，索引中有5个文档，匹配的文档书为4。因为使用的是范围查询，所以匹配的文档得分都为1.如果想提升在上述排序中前两个名称包含“金都”的酒店文档排名。而这两个目标酒店的位置分别为2和3，当前的索引主分片数为1，那么应该设置window_size=3，使用二次打分对查询进行扩展的DSL如下：
GET /hotel_painless/_search
{
"query": {
"range": {
"price": { //使用range查询
"gte": 300
}
}
},
"rescore": {
"query": { //对返回的文档进行二次打分
"rescore_query":{
"match":{
"title":"金都"
}
}
},
"window_size": 3 //对每个分片的前3个文档进行二次打分
}
}
在上面的DSL中，二次打分使用rescore进行封装，在rescore中可以设置二次打分的查询query和window_size，window_size设置为3意味着对每个分片的前3个文档进行二次打分，执行上述DSL的结果如下：
{
...
"hits" : {
"total" : {
"value" : 4,
"relation" : "eq"
},
"max_score" : 2.1062784,
"hits" : [
{
"_index" : "hotel_painless",
"_type" : "_doc",
"_id" : "004",
"_score" : 2.1062784,
"_source" : {
"title" : "金都家至酒店",
"price" : 500.0,
...
}
},
{
"_index" : "hotel_painless",
"_type" : "_doc",
"_id" : "002",
"_score" : 1.977973,
"_source" : {
"title" : "金都嘉怡假日酒店",
"price" : 337.0,
...
}
},
{
"_index" : "hotel_painless",
"_type" : "_doc",
"_id" : "001",
"_score" : 1.0,
"_source" : {
"title" : "文雅假日酒店",
"price" : 556.0,
}
},
{
"_index" : "hotel_painless",
"_type" : "_doc",
"_id" : "005",
"_score" : 1.0,
"_source" : {
"title" : "文雅精选酒店",
...
}
}
]
}
}
通过对比rescore前后的结果可以看到，原有文档的002和004分别排在第二位和第三位，并且得分都是1。在rescore的查询中对TOP3且标题含有“金都”的文档进行了加分操作，因此文档002和文档004的得分得到了提升。因为文档004的标题更短，所以它的分数相对更高一些，处在第一个位置，文档002处在第二个位置。
在默认情况下，当存在二次打分时,$文档得分=原始查询分数+二次打分分数$
而用户额可以为这两部分的分数设置权重，所以$文档得分=原始查询分数\times 原始查询权重+二次打分分数\times 二次打分权重$
可以分别设置query_weight和rescore_query_weight，为原始查询权重和二次打分权重赋值，例如下面的DSL设置原始查询权重为0.6，二次打分权重为1.7：
GET /hotel_painless/_search
{
"query": {
"range": {
"price": {
"gte": 300
}
}
},
"rescore": {
"query": {
"rescore_query": {
"match": {
"title": "金都"
}
},
"query_weight": 0.6,
"rescore_query_weight": 1.7
},
"window_size": 3
}
}
1.3 在Java客户端中使用二次打分
@Test
public void getRescoreQuery(){
//构建原始的range查询
RangeQueryBuilder rangeQueryBuilder = QueryBuilders.rangeQuery("price")
.gte(300);
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
searchSourceBuilder.query(rangeQueryBuilder);//添加原始查询Builder
//构建二次打分的查询
MatchQueryBuilder matchQueryBuilder = QueryBuilders.matchQuery("title", "金都");
//构建二次打分Builder
QueryRescorerBuilder queryRescorerBuilder = new QueryRescorerBuilder(matchQueryBuilder);
queryRescorerBuilder.setQueryWeight(0.6f); //设置原始打分权重
queryRescorerBuilder.setRescoreQueryWeight(1.7f); //设置二次打分权重
queryRescorerBuilder.windowSize(3); //设置每个分片参加二次打分文档的个数
//添加二次打分Builder
searchSourceBuilder.addRescorer(queryRescorerBuilder);
//创建搜索请求
SearchRequest searchRequest = new SearchRequest("hotel_painless");
searchRequest.source(searchSourceBuilder);//设置查询请求
printResult(searchRequest); //打印搜索结果
}
//打印方法封装，方便查看结果
public void printResult(SearchRequest searchRequest) {
try {
//执行搜索
SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
//获取搜索结果集
SearchHits searchHits = searchResponse.getHits();
for (SearchHit searchHit : searchHits) {
String index=searchHit.getIndex(); //获取索引名称
String id=searchHit.getId(); //获取文档_id
float score = searchHit.getScore(); //获取得分
String source = searchHit.getSourceAsString();//获取文档内容
System.out.println("index="+index+",id="+id+",score="+score+",source="+source);
}
} catch (IOException e) {
throw new RuntimeException(e);
}
}
