Elasticsearch(036)：es中批量操作之mget(批量查询)
mget(批量查询)
一、介绍
mget是es提供的一种批量的读取操作的API。
mget API允许根据索引，类型（可选）和id（以及可能的路由）获取多个文档。响应包括一个docs数组。该数组具有与原始多重获取请求相对应的所有提取文档（如果特定的get失败，则在响应中包含包含此错误的对象）。成功获取的结构与get API提供的文档的结构相似。
二、示例用法
2.1 测试数据准备
示例索引结构如下
PUT examplePUT example/docs/_mapping{"properties": {"id": { "type": "long"},"name": { "type": "text"},"counter": { "type": "integer"},"tags": { "type": "text"}}}PUT example/docs/1{"id": 1,"name": "admin","counter": 1,"tags": ["gray"]}PUT example/docs/2{"id": 2,"name": "zhangsan","counter": 1,"tags": ["black"]}PUT example/docs/3{"id": 3,"name": "lisi","counter": 1,"tags": ["purple"]}PUT example_testPUT example_test/docs/_mapping{"properties": {"id": { "type": "long"},"name": { "type": "text"},"counter": { "type": "integer"},"tags": { "type": "text"}}}PUT example_test/docs/1{"id": 1,"name": "test-admin","counter": 1,"tags": ["gray"]}PUT example_test/docs/2{"id": 2,"name": "test-zhangsan","counter": 1,"tags": ["black"]}PUT example_test/docs/3{"id": 3,"name": "test-lisi","counter": 1,"tags": ["purple"]}#查询example所有数据GET example/docs/_search{"query": {"match_all": { }}}#查询example_test所有数据GET example_test/docs/_search{"query": {"match_all": { }}}
2.2 传统的单条查询，在面对需要查询多个时，需要一次次发送请求到es
示例查询
GET example/docs/1GET example/docs/2GET example_test/docs/1GET example_test/docs/2
这样其实局限性，多次的网络请求很容易造成资源浪费和降低性能。
2.3 mget之查询（index不同）
示例如下
GET _mget{"docs": [{"_index": "example","_type": "docs","_id": "1"},{"_index": "example","_type": "docs","_id": "2"},{"_index": "example_test","_type": "docs","_id": "1"},{"_index": "example_test","_type": "docs","_id": "2"}]}
返回数据如下
{"docs": [{"_index": "example","_type": "docs","_id": "1","_version": 1,"found": true,"_source": {"id": 1,"name": "admin","counter": 1,"tags": ["gray"]}},{"_index": "example","_type": "docs","_id": "2","_version": 1,"found": true,"_source": {"id": 2,"name": "zhangsan","counter": 1,"tags": ["black"]}},{"_index": "example_test","_type": "docs","_id": "1","_version": 1,"found": true,"_source": {"id": 1,"name": "test-admin","counter": 1,"tags": ["gray"]}},{"_index": "example_test","_type": "docs","_id": "2","_version": 1,"found": true,"_source": {"id": 2,"name": "test-zhangsan","counter": 1,"tags": ["black"]}}]}
2.4 mget之查询（index相同，type不同）
不建议掌握，type有可能在后续的版本废除。这里只做一下简单示例。
GET _mget{"docs": [{"_index": "example","_type": "docs1","_id": "1"},{"_index": "example","_type": "docs2","_id": "1"},]
2.5 mget之查询（index相同，type相同）。
示例如下
GET _mget{"docs": [{"_index": "example","_type": "docs","_id": "1"},{"_index": "example","_type": "docs","_id": "2"},{"_index": "example","_type": "docs","_id": "3"}]}#index和type相同的话可以简化成如下GET example/docs/_mget{"docs": [{"_id": "1"},{"_id": "2"},{"_id": "3"}]}
返回结果
{"docs": [{"_index": "example","_type": "docs","_id": "1","_version": 1,"found": true,"_source": {"id": 1,"name": "admin","counter": 1,"tags": ["gray"]}},{"_index": "example","_type": "docs","_id": "2","_version": 1,"found": true,"_source": {"id": 2,"name": "zhangsan","counter": 1,"tags": ["black"]}},{"_index": "example","_type": "docs","_id": "3","_version": 1,"found": true,"_source": {"id": 3,"name": "lisi","counter": 1,"tags": ["purple"]}}]}
mget是很重要的，一般来说，进行查询的时候，如果一次性查询多条数据的话，那么一定要用batch批量操作的api，尽可能减少网络开销次数，可以将性能大幅度提升。
雨点打透心脏的1/2处
不念不忘少年蓝@
￡神魔★判官ぃ
分手后的思念是犯贱
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