mongodb

MongoDB uses COLLSCAN when returning just _id

由 时光毁灭记忆、已成空白 提交于 2021-02-18 07:51:50
问题 I want to return all IDs from a MongoDB collection and I used the code below: db.coll.find({}, { _id: 1}) But MongoDB scans the whole collection instead of reading the information from the default index { _id: 1 } . From the log: { find: "collection", filter: {}, projection: { _id: 1 } } planSummary: COLLSCAN cursorid:30463374118 keysExamined:0 docsExamined:544783 numYields:4286 nreturned:544782 reslen:16777238 locks:{ Global: { acquireCount: { r: 8574 } }, Database: { acquireCount: { r: 4287

MongoDB uses COLLSCAN when returning just _id

由 帅比萌擦擦* 提交于 2021-02-18 07:51:27
问题 I want to return all IDs from a MongoDB collection and I used the code below: db.coll.find({}, { _id: 1}) But MongoDB scans the whole collection instead of reading the information from the default index { _id: 1 } . From the log: { find: "collection", filter: {}, projection: { _id: 1 } } planSummary: COLLSCAN cursorid:30463374118 keysExamined:0 docsExamined:544783 numYields:4286 nreturned:544782 reslen:16777238 locks:{ Global: { acquireCount: { r: 8574 } }, Database: { acquireCount: { r: 4287

上亿数据怎么玩深度分页？兼容MySQL + ES + MongoDB

由 别来无恙 提交于 2021-02-18 07:36:41
面试题 & 真实经历 面试题 ：在数据量很大的情况下，怎么实现深度分页？ 大家在面试时，或者准备面试中可能会遇到上述的问题，大多的回答基本上是 分库分表建索引 ，这是一种很 标准的正确回答 ，但现实总是很骨感，所以面试官一般会追问你一句， 现在工期不足，人员不足，该怎么实现深度分页？ 这个时候没有实际经验的同学基本麻爪，So，请听我娓娓道来。 惨痛的教训 首先必须明确一点 ：深度分页可以做，但是 深度随机跳页绝对需要禁止。 上一张图： 你们猜，我点一下第 142360 页，服务会不会爆炸？ 像 MySQL ， MongoDB 数据库还好，本身就是专业的数据库，处理的不好，最多就是慢，但如果涉及到 ES ，性质就不一样了，我们不得不利用 SearchAfter Api，去循环获取数据，这就牵扯到内存占用的问题，如果当时代码写的不优雅，直接就可能导致内存溢出。 为什么不能允许随机深度跳页 从技术的角度浅显的聊一聊为什么不能允许随机深度跳页，或者说为什么不建议深度分页 MySQL 分页的基本原理： SELECT * FROM test ORDER BY id DESC LIMIT 10000, 20; LIMIT 10000 , 20的意思扫描满足条件的10020行，扔掉前面的10000行，返回最后的20行。如果是LIMIT 1000000 , 100，需要扫描1000100 行

Relational database design to mongoDB/mongoose design

由 自作多情 提交于 2021-02-18 06:41:09
问题 I have recently started using mongoDB and mongoose for my new node.js application. Having only used relational databases before I am struggling to adapt to the mongoDB/noSQL way of thinking such as denormalization and lack of foreign key relationships. I have this relational database design: **Users Table** user_id username email password **Games Table** game_id game_name **Lobbies Table** lobby_id game_id lobby_name **Scores Table** user_id game_id score So, each lobby belongs to a game, and

Mongoose find all documents where array.length is greater than 0 & sort the data

由 血红的双手。 提交于 2021-02-18 04:13:44
问题 I am using mongoose to perform CRUD operation on MongoDB. This is how my schema looks. var EmployeeSchema = new Schema({ name: String, description: { type: String, default: 'No description' }, departments: [] }); Each employee can belong to multiple department. Departments array will look like [1,2,3]. In this case departments.length = 3. If the employee does not belong to any department, the departments.length will be equal to 0. I need to find all employee where EmployeeSchema.departments

Mongoose find all documents where array.length is greater than 0 & sort the data

由 拥有回忆 提交于 2021-02-18 04:07:40
问题 I am using mongoose to perform CRUD operation on MongoDB. This is how my schema looks. var EmployeeSchema = new Schema({ name: String, description: { type: String, default: 'No description' }, departments: [] }); Each employee can belong to multiple department. Departments array will look like [1,2,3]. In this case departments.length = 3. If the employee does not belong to any department, the departments.length will be equal to 0. I need to find all employee where EmployeeSchema.departments

Mongoose find all documents where array.length is greater than 0 & sort the data

由 我的未来我决定 提交于 2021-02-18 04:07:13
问题 I am using mongoose to perform CRUD operation on MongoDB. This is how my schema looks. var EmployeeSchema = new Schema({ name: String, description: { type: String, default: 'No description' }, departments: [] }); Each employee can belong to multiple department. Departments array will look like [1,2,3]. In this case departments.length = 3. If the employee does not belong to any department, the departments.length will be equal to 0. I need to find all employee where EmployeeSchema.departments

Call Mongodb stored function from PHP7

由 倖福魔咒の 提交于 2021-02-18 03:19:58
问题 Below is my mongodb function that is stored in Mongodb. db.system.js.save( { _id: "echoFunction", value : function(x) { return x; } } ) I can call this function in mongo using below query : db.loadServerScripts(); echoFunction(3); Now i want to call this function from PHP 7. and also help with laravel. 回答1: You can use following code snippet from laravel to execute your mongoDB function. $cursor = DB::connection('mongodb')->command(array('eval' => 'echoFunction("4")')); $data = $cursor-

Call Mongodb stored function from PHP7

由 浪子不回头ぞ 提交于 2021-02-18 03:17:22
问题 Below is my mongodb function that is stored in Mongodb. db.system.js.save( { _id: "echoFunction", value : function(x) { return x; } } ) I can call this function in mongo using below query : db.loadServerScripts(); echoFunction(3); Now i want to call this function from PHP 7. and also help with laravel. 回答1: You can use following code snippet from laravel to execute your mongoDB function. $cursor = DB::connection('mongodb')->command(array('eval' => 'echoFunction("4")')); $data = $cursor-

MongoDB和Java（6）：Spring Data整合MongoDB副本集、分片集群

由 a 夏天 提交于 2021-02-18 02:17:58
最近花了一些时间学习了下MongoDB数据库，感觉还是比较全面系统的，涉及了软件安装、客户端操作、安全认证、副本集和分布式集群搭建，以及使用Spring Data连接MongoDB进行数据操作，收获很大。特此记录，以备查看。 文章目录： MongoDB和Java（1）：Linux下的MongoDB安装 MongoDB和Java（2）：普通用户启动mongod进程 MongoDB和Java（3）：Java操作MongoB MongoDB和Java（4）：Spring Data整合MongoDB（XML配置） MongoDB和Java（5）：Spring Data整合MongoDB（注解配置） MongoDB和Java（6）：Spring Data整合MongoDB副本集、分片集群 MongoDB和Java（7）：MongoDB用户管理 本文记录如何整合Spring data和MongoDB副本集、分片集群。 Java客户端这边的开发环境和《 MongoDB和Java（5）：Spring Data整合MongoDB（注解配置） 》是一样的，实体类、数据层接口、测试类代码都不需要太多的改动，主要需要改的就是mongo的连接属性文件、MongoClient的创建方式。 源代码下载 MongoDB和Java学习代码.zip 1、副本集环境 主：10.10.13.195:27017 从：10
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