Book Image

Learn MongoDB 4.x

By : Doug Bierer
Book Image

Learn MongoDB 4.x

By: Doug Bierer

Overview of this book

When it comes to managing a high volume of unstructured and non-relational datasets, MongoDB is the defacto database management system (DBMS) for DBAs and data architects. This updated book includes the latest release and covers every feature in MongoDB 4.x, while helping you get hands-on with building a MongoDB database app. You’ll get to grips with MongoDB 4.x concepts such as indexes, database design, data modeling, authentication, and aggregation. As you progress, you’ll cover tasks such as performing routine operations when developing a dynamic database-driven website. Using examples, you’ll learn how to work with queries and regular database operations. The book will not only guide you through design and implementation, but also help you monitor operations to achieve optimal performance and secure your MongoDB database systems. You’ll also be introduced to advanced techniques such as aggregation, map-reduce, complex queries, and generating ad hoc financial reports on the fly. Later, the book shows you how to work with multiple collections as well as embedded arrays and documents, before finally exploring key topics such as replication, sharding, and security using practical examples. By the end of this book, you’ll be well-versed with MongoDB 4.x and be able to perform development and administrative tasks associated with this NoSQL database.
Table of Contents (22 chapters)
Section 1: Essentials
Section 2: Building a Database-Driven Web Application
Section 3: Digging Deeper
Section 4: Replication, Sharding, and Security in a Financial Environment
Working with Complex Documents Across Collections

Reading from a sharded cluster

As mentioned earlier, you need to configure your application to connect to a mongos instance in order to retrieve full results from all shards.

However, it is extremely important to note that although you can perform queries without using the shard key, it forces the mongos instance to perform a broadcast operation. As mentioned earlier, this operation first sends out a query to all shards before retrieving the data. In addition, if you do not include the shard key in the query, its index is not used, further degrading performance.

As an example, from the sample data, let's assume that the management wants a count of all world_cities documents in England. The main difference in your program code is that you need to connect to a mongos instance rather than a mongod instance. Here is a sample program that achieves this result:

from pymongo import MongoClient
hostName = 'mongos1.biglittle...