Search 的分页与去重
介绍ES分页和ES去重的实现方式。
简单分页
from + size
每次对结果集都是全面分页，数量少时可以用，10000条以内(index.max_result_window的默认值)。对很占内存。10个一条 深度就是1000。控制分页的深度意在控制协调节点上的队列长度。
GET /sales/_search
{
"from" : 0, "size" : 2,
"query" : {
"term" : { "type" : "hat" }
}
}
问题说明
一个有 5 个主分片的索引中搜索。 当我们请求结果的第一页（结果从 1 到 10 ），每一个分片产生前 10 的结果，并且返回给 协调节点 ，协调节点对 50 个结果排序得到全部结果的前 10 个。
现在假设我们请求第 990 页–结果从 990 到 1000 。所有都以相同的方式工作除了每个分片不得不产生前1000个结果以外。 然后协调节点对全部 5000 个结果排序最后丢弃掉这些结果中的 4990 个结果。
可以看到，在分布式系统中，对结果排序的成本随分页的深度成指数上升。这就是 web 搜索引擎对任何查询都不要返回超过 10000 个结果的原因。
深度分页
search after
使用上一页的结果来帮助实时检索下一页。
分页都是伴随着排序的，这里游标尽量使用一个具有唯一性的字段来担任。如果使用具有相同排序值的字段，可能会导致结果的丢失或重复（分页不准）。search_after 会查找与tiebreaker提供的值完全或部分匹配的第一个文档。
search_after 不是自由跳转到随机页面的解决方案，而是并行滚动多个查询的解决方案。 它与 scroll API 非常相似，但不同的是，search_after 参数是无状态的，它总是针对最新版本的搜索器进行解析。 因此，排序顺序可能会在遍历期间根据索引的更新和删除而改变。
❗️search after字段要求
- 排序字段要求开启
doc_value。 -
from的值必须是0或者-1。
GET /sales/_search
{
"size": 2,
"query": {
"match" : {
"type" : "hat"
}
},
"search_after":[1422748800000],
"sort": [
{"date": "asc"}
]
}
scroll
scrolling用于处理大量数据。滚动上下文成本高昂，不推荐将其用于实时用户请求。在使用srcoll时，是创建一个快照，所以当有新的数据写入，无法被查询到。
POST /sales/_search?scroll=1m
{
"size": 100,
"query": {
"match" : {
"type" : "elasticsearch"
}
}
}
上述请求的结果包括一个 _scroll_id，它应该传递给滚动 API 以检索下一批结果。
POST /_search/scroll
{
"scroll" : "1m",
"scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAAAAD4WYm9laVYtZndUQlNsdDcwakFMNjU1QQ=="
}
当超过滚动超时时长，搜索上下文会自动删除。 然而，保持分页打开是有代价的，如上一节所述，因此一旦不再使用该分页，就应该使用 clear-scroll API 明确清除该分页：
DELETE /_search/scroll
{
"scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAAAAD4WYm9laVYtZndUQlNsdDcwakFMNjU1QQ=="
}
详细使用可以参考Search的滚动查询（Scroll）
字段折叠（去重）
Field Collapsing
允许根据字段值折叠搜索结果。 折叠是通过每个折叠键仅选择排序最靠前的文档来完成的。 例如，下面的查询检索每个用户的最佳推文，并按喜欢的数量对其进行排序。
❗️ 折叠字段要求：
- 类型必须是 [
keyword]或 [numeric] - [
doc_values]已激活
GET /twitter/_search
{
"query": {
"match": {
"message": "elasticsearch"
}
},
"collapse" : {
"field" : "user"
},
"sort": ["likes"],
"from": 10
}
-
collapse：使用“user”字段折叠结果集。 -
sort：按喜欢的数量对顶级文档进行排序。 -
from：定义第一个折叠结果的偏移量。
⚠️响应中的总命中数表示没有折叠的匹配文档的数量。 各个分组的数量是未知的。
下方例子是去查询sales，按type分组，在以price倒序排序，获取每组最大的商品价格。
GET /sales/_search
{
"collapse" : {
"field" : "type"
},
"sort": [{"price":{"order" : "desc"}}]
}
展开折叠结果 Expand collapse results
可以使用 inner_hits 选项展开每个折叠的热门点击。
GET /twitter/_search
{
"query": {
"match": {
"message": "elasticsearch"
}
},
"collapse" : {
"field" : "user",
"inner_hits": {
"name": "last_tweets",
"size": 5,
"sort": [{ "date": "asc" }]
},
"max_concurrent_group_searches": 4
},
"sort": ["likes"]
}
-
collapse.field：使用“user”字段折叠结果集。 -
collapse.inner_hits.name：用于响应中内部命中部分的名称。 -
collapse.inner_hits.size：每个折叠键要检索的 inner_hits 数。 -
collapse.inner_hits.sort：如何对每个组内的文档进行排序。 -
max_concurrent_group_searches： 每组允许检索 inner_hits 的并发请求数。
下方例子是去查询sales，按type分组，在以price倒序排序，获取每组最大的商品价格。同时通过inner_hits将每组的的Top 5展示出来。
GET /sales/_search
{
"collapse" : {
"field" : "type",
"inner_hits": {
"name": "XXX",
"size": 5,
"sort": [{ "price": "desc" }]
}
},
"sort": [{"price":{"order" : "desc"}}]
}
Possible response:
{
"took": 6,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 7,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "N1wXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
},
"fields": {
"type": [
"hat"
]
},
"sort": [
200
],
"inner_hits": {
"XXX": {
"hits": {
"total": 3,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "N1wXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
},
"sort": [
200
]
},
{
"_index": "sales",
"_type": "_doc",
"_id": "PFwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/03/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
},
"sort": [
200
]
},
{
"_index": "sales",
"_type": "_doc",
"_id": "OlwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/02/01 00:00:00",
"price": 50,
"promoted": false,
"rating": 1,
"type": "hat"
},
"sort": [
50
]
}
]
}
}
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "OFwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "t-shirt"
},
"fields": {
"type": [
"t-shirt"
]
},
"sort": [
200
],
"inner_hits": {
"XXX": {
"hits": {
"total": 3,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "OFwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "t-shirt"
},
"sort": [
200
]
},
{
"_index": "sales",
"_type": "_doc",
"_id": "PVwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/03/01 00:00:00",
"price": 175,
"promoted": false,
"rating": 2,
"type": "t-shirt"
},
"sort": [
175
]
},
{
"_index": "sales",
"_type": "_doc",
"_id": "O1wXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/02/01 00:00:00",
"price": 10,
"promoted": true,
"rating": 4,
"type": "t-shirt"
},
"sort": [
10
]
}
]
}
}
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "OVwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 150,
"promoted": true,
"rating": 5,
"type": "bag"
},
"fields": {
"type": [
"bag"
]
},
"sort": [
150
],
"inner_hits": {
"XXX": {
"hits": {
"total": 1,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "OVwXRYMBCLf16WD0DCm6",
"_score": null,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 150,
"promoted": true,
"rating": 5,
"type": "bag"
},
"sort": [
150
]
}
]
}
}
}
}
]
}
}
二级折叠 Second level of collapsing 二次去重
还支持第二级折叠并应用于inner_hits。 例如，以下请求查找每个国家/地区得分最高的推文，并在每个国家/地区内查找每个用户得分最高的推文。
GET /twitter/_search
{
"query": {
"match": {
"message": "elasticsearch"
}
},
"collapse" : {
"field" : "country",
"inner_hits" : {
"name": "by_location",
"collapse" : {"field" : "user"},
"size": 3
}
}
}
-
collapse.field：使用“country”字段折叠结果集，一级折叠字段。 -
collapse.inner_hits.name：用于响应中内部命中部分的名称。 -
collapse.inner_hits.size：每个折叠键要检索的 inner_hits 数。 -
collapse.inner_hits.collapse：使用“user”字段折叠结果集，二级折叠字段。
Top Hits Aggregation
top_hits 指标聚合器跟踪要聚合的最相关文档。 该聚合器旨在用作子聚合器，以便可以按桶分区汇总最匹配的文档。
top_hits 聚合器可以有效地用于通过存储桶聚合器按某些字段对结果集进行分组。 一个或多个存储桶聚合器确定将结果集切成哪些属性。
Options
-
from- 获取的第一个结果的偏移量。 -
size- 每个桶返回的最大匹配命中数。 默认情况下，返回前三个匹配的命中。 -
sort- 应该如何对最匹配的匹配项进行排序。 默认情况下，命中按主查询的分数排序。
在下面的示例中，我们按类型对销售进行分组，并按商品类型显示最后一次销售。 对于每次销售，源中仅包含日期和价格字段。
POST /sales/_search?size=0
{
"aggs": {
"top_tags": {
"terms": {
"field": "type",
"size": 3
},
"aggs": {
"top_sales_hits": {
"top_hits": {
"sort": [
{
"date": {
"order": "desc"
}
}
],
"_source": {
"includes": [ "date", "price" ]
},
"size" : 1
}
}
}
}
}
}
Possible response:
{
...
"aggregations": {
"top_tags": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "hat",
"doc_count": 3,
"top_sales_hits": {
"hits": {
"total": 3,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "AVnNBmauCQpcRyxw6ChK",
"_source": {
"date": "2015/03/01 00:00:00",
"price": 200
},
"sort": [
1425168000000
],
"_score": null
}
]
}
}
},
{
"key": "t-shirt",
"doc_count": 3,
"top_sales_hits": {
"hits": {
"total": 3,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "AVnNBmauCQpcRyxw6ChL",
"_source": {
"date": "2015/03/01 00:00:00",
"price": 175
},
"sort": [
1425168000000
],
"_score": null
}
]
}
}
},
{
"key": "bag",
"doc_count": 1,
"top_sales_hits": {
"hits": {
"total": 1,
"max_score": null,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "AVnNBmatCQpcRyxw6ChH",
"_source": {
"date": "2015/01/01 00:00:00",
"price": 150
},
"sort": [
1420070400000
],
"_score": null
}
]
}
}
}
]
}
}
}
字段折叠
字段折叠或结果分组是一种将结果集逻辑分组并按组返回顶部文档的功能。 组的顺序由组中第一个文档的相关性决定。 在 Elasticsearch 中，这可以通过将 top_hits 聚合器包装为子聚合器的存储桶聚合器来实现。
在下面的示例中，我们按商品类型对销售进行分组，分组时返回Top 3，再对每组商品取价格最大的记录，从结果集中展示。top_hit中只是取最大的那个值。
POST /sales/_search
{
"aggs": {
"top_tags": {
"terms": {
"field": "type",
"size": 3
},
"aggs": {
"top_sales_hits": {
"top_hits": {
"size": 1,
"_source": {
"includes": [
"date",
"price"
]
}
}
},
"top_hit": {
"max": {
"field": "price"
}
}
}
}
}
}
Possible response:
{
...
"aggregations": {
"top_tags": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "hat",
"doc_count": 3,
"top_sales_hits": {
"hits": {
"total": 3,
"max_score": 1,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "N1wXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "OlwXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/02/01 00:00:00",
"price": 50,
"promoted": false,
"rating": 1,
"type": "hat"
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "PFwXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/03/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
}
}
]
}
},
"top_hit": {
"value": 200
}
},
{
"key": "t-shirt",
"doc_count": 3,
"top_sales_hits": {
"hits": {
"total": 3,
"max_score": 1,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "O1wXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/02/01 00:00:00",
"price": 10,
"promoted": true,
"rating": 4,
"type": "t-shirt"
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "OFwXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "t-shirt"
}
},
{
"_index": "sales",
"_type": "_doc",
"_id": "PVwXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/03/01 00:00:00",
"price": 175,
"promoted": false,
"rating": 2,
"type": "t-shirt"
}
}
]
}
},
"top_hit": {
"value": 200
}
},
{
"key": "bag",
"doc_count": 1,
"top_sales_hits": {
"hits": {
"total": 1,
"max_score": 1,
"hits": [
{
"_index": "sales",
"_type": "_doc",
"_id": "OVwXRYMBCLf16WD0DCm6",
"_score": 1,
"_source": {
"date": "2015/01/01 00:00:00",
"price": 150,
"promoted": true,
"rating": 5,
"type": "bag"
}
}
]
}
},
"top_hit": {
"value": 150
}
}
]
}
}
}
Cardinality Aggregation 去重后的计数
计算不同值的近似计数的single-value指标聚合。 值可以从文档中的特定字段中提取或由脚本生成。
以下例子是，查询销售索引中商品类型一种几种，先对type进行去重，在对结果进行计数。
POST /sales/_search
{
"aggs" : {
"type_count" : {
"cardinality" : {
"field" : "type"
}
}
}
}
Response:
{
...
"aggregations" : {
"type_count" : {
"value" : 3
}
}
}
测试数据
新建索引
PUT sales
{
"settings:": {
"number_of_shards": 2,
"number_of_replicas": 1
},
"mappings": {
"_doc": {
"properties": {
"type": {
"type": "keyword"
}
}
}
}
}
写入数据
POST /sales/_doc/_bulk?refresh
{"index": {}}
{
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
}
{"index": {}}
{
"date": "2015/01/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "t-shirt"
}
{"index": {}}
{
"date": "2015/01/01 00:00:00",
"price": 150,
"promoted": true,
"rating": 5,
"type": "bag"
}
{"index": {}}
{
"date": "2015/02/01 00:00:00",
"price": 50,
"promoted": false,
"rating": 1,
"type": "hat"
}
{"index": {}}
{
"date": "2015/02/01 00:00:00",
"price": 10,
"promoted": true,
"rating": 4,
"type": "t-shirt"
}
{"index": {}}
{
"date": "2015/03/01 00:00:00",
"price": 200,
"promoted": true,
"rating": 1,
"type": "hat"
}
{"index": {}}
{
"date": "2015/03/01 00:00:00",
"price": 175,
"promoted": false,
"rating": 2,
"type": "t-shirt"
}
注意事项
-
collapse无法在深度分页中使用-
collapse不可以和search_after一起使用 -
collapse不可以和scroll一起使用
{"type":"search_context_exception","reason":"cannot use `collapse` in conjunction with `search_after`"}{"type":"search_context_exception","reason":"cannot use `collapse` in a scroll context"} -
-
collapse与Aggregation联用时计算的并非当页的数据而是全部数据。比如下例：文章来源：https://www.toymoban.com/news/detail-425204.htmlPOST /sales/_search { "from": 0, "size": 2, "sort": [ "date" ], "collapse": { "field": "type" }, "aggs": { "type_count": { "cardinality": { "field": "type" } } } }Response:文章来源地址https://www.toymoban.com/news/detail-425204.html
{ ... "hits": { "total": 7, "max_score": null, "hits": [ { "_index": "sales", "_type": "_doc", "_id": "N1wXRYMBCLf16WD0DCm6", "_score": null, "_source": { "date": "2015/01/01 00:00:00", "price": 200, "promoted": true, "rating": 1, "type": "hat" }, "fields": { "type": [ "hat" ] }, "sort": [ 1420070400000 ] }, { "_index": "sales", "_type": "_doc", "_id": "OVwXRYMBCLf16WD0DCm6", "_score": null, "_source": { "date": "2015/01/01 00:00:00", "price": 150, "promoted": true, "rating": 5, "type": "bag" }, "fields": { "type": [ "bag" ] }, "sort": [ 1420070400000 ] } ] }, "aggregations": { "type_count": { "value": 3 } } }
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