事情起因：我们使用es作为日志搜索引擎，客户收集到的业务日志非常之大，每次查询后，返回页数较多，由于我们web界面限制每页返回150条，当客户翻到66页之后就会报错。

报错信息如下：

• Elasticsearch limits the search result to 10000 messages. With a page size of 150 messages, you can use the first 66 pages. Unable to perform search query: Elasticsearch exception [type=illegal_argument_exception, reason=Result window is too large, from + size must be less than or equal to: [10000] but was [34050]. See the scroll api for a more efficient way to request large data sets. This limit can be set by changing the [index.max_result_window] index level setting.].

一、Search after介绍

        使用Search after作为查询，默认情况下我们使用Scroll search作为查询，可以指定From + size 大小的数据批量返回，这是为了防止因为请求过多的结果而导致内存和CPU资源过度消耗。

        查询结果的分页可以通过使用from and size 来完成，但是当达到深度分页时，成本变得令人望而却步。 默认为 10000 是一种保护措施，搜索请求占用的堆内存和时间成正比。 建议使用 scroll API 来实现高效的深度滚动，但滚动上下文成本高昂，而且成本不高，建议将其用于实时用户请求。 Search after通过提供实时游标来规避此问题。 这个想法是使用上一页的结果来帮助检索下一页。

二、实验

1.默认生成20条数据

for i in `seq 1 20`
do echo 192.168.113.195 -d -P 54000 "zhongguoren $i"sleep 1
done

2.默认查询

GET index_1/_search
{"query": {"match": {"message": "zhongguoren"}},"sort": [{"timestamp": "asc"}]
}

3.Search after查询

index_1/_search
{"size": 10,"query": {"match": {"message": "zhongguoren"}},"sort": [{"timestamp": "asc"},{"_id": "asc"}]
}

先查询前10条，这个和之前默认查询有个区别，就是排序时通过timestamp和_id进行同时排序，在查询结果中得到一个sort字段，值为

"sort": [ - 
          1680770417895,
          "a894bf71-d456-11ed-aa52-000c29f6b211"
        ]

查询后结果值为：

{ - "took": 223,"timed_out": false,"_shards": { - "total": 4,"successful": 4,"skipped": 0,"failed": 0},"hits": { - "total": { - "value": 20,"relation": "eq"},"max_score": null,"hits": [ - { - "_index": "12_149","_type": "_doc","_id": "2df06a80-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 35834,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVC899ZZXDJXF453F0RVXJ","message": "<5>Apr 6 16:36:52 root: zhongguoren 1","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:36:52.135"},"sort": [ - 1680770212135,"2df06a80-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "5244ccf0-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 52885,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVE3XCWZK71D74YVF58PZ2","message": "<5>Apr 6 16:37:53 root: zhongguoren 2","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:37:53.086"},"sort": [ - 1680770273086,"5244ccf0-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "5e46d610-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 57417,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVEQFJP3CN17A2NG41YYHY","message": "<5>Apr 6 16:38:13 root: zhongguoren 3","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:38:13.232"},"sort": [ - 1680770293232,"5e46d610-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "644eb870-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 52483,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVF1BQNJZ48GW39G48DQNQ","message": "<5>Apr 6 16:38:23 root: zhongguoren 4","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:38:23.350"},"sort": [ - 1680770303350,"644eb870-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a562e070-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 45404,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJC1YT9SPVWG81CJGBMXG","message": "<5>Apr 6 16:40:12 root: zhongguoren 5","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:12.534"},"sort": [ - 1680770412534,"a562e070-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a609f5e0-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 33127,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJD1Y45HAS4N7ZN2YXWS0","message": "<5>Apr 6 16:40:13 root: zhongguoren 6","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:13.629"},"sort": [ - 1680770413629,"a609f5e0-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a6a328a0-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 41301,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJE1A0ER5S5BZ8DJKW2A6","message": "<5>Apr 6 16:40:14 root: zhongguoren 7","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:14.633"},"sort": [ - 1680770414633,"a6a328a0-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a73c3451-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 36916,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJF0PXMNPGKVZ7YEJ1JNY","message": "<5>Apr 6 16:40:15 root: zhongguoren 8","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:15.637"},"sort": [ - 1680770415637,"a73c3451-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a7dfc750-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 140,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 42778,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJG26BRZG09JSSA96S329","message": "<5>Apr 6 16:40:16 root: zhongguoren 9","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:16.708"},"sort": [ - 1680770416708,"a7dfc750-d456-11ed-aa52-000c29f6b211"]},{ - "_index": "12_149","_type": "_doc","_id": "a894bf71-d456-11ed-aa52-000c29f6b211","_score": null,"_source": { - "elap_accounted_message_size": 141,"elap_source_input": "636c90d3246ca975ec999b24","streams": [ - "6969696969697379736c6f67","6969696969727379736c6f67"],"elap_remote_port": 53090,"elap_source_node": "5bb5d963-7fdd-4e2d-bfdf-a5069bb07097","source": "192.168.113.195","elap_message_id": "01GXAVJH78H4GCQ44KNZQ1MQ0H","message": "<5>Apr 6 16:40:17 root: zhongguoren 10","elap_remote_ip": "192.168.113.195","timestamp": "2023-04-06 08:40:17.895"},"sort": [ - 1680770417895,"a894bf71-d456-11ed-aa52-000c29f6b211"]}]}
}

4.Search after二次查询

可以根据sort值带入到后续得search after中，以做到从某点进行再次查询。

GET index_1/_search
{"size": 10,"query": {"match": {"message": "zhongguoren"}},"search_after": [1680770417895,"a894bf71-d456-11ed-aa52-000c29f6b211"],"sort": [{"timestamp": "asc"},{"_id": "asc"}]
}

返回结果中，得到11-20条数据。

总结