What is CQRS and why do you need it as a developer?

For instance:

• User Management -> CRUD
• Invoicing -> CRUD
• Insurance Policy Management (the Core Domain) -> CQRS

• Separating write from read activities allows the use of the best database technology (a SQL database for writing and a non-SQL database for reading).
• Reducing response latency by placing read data sources in strategic geolocations for better performance.
• Provides more efficient scaling of storage capacity based on real-world usage.

• Requires expertise in a variety of database technologies.
• Higher costs in terms of hardware or if a cloud provider is used.
• Requires special consideration in terms of Service Level Agreements.
• More points of failure, which implies comprehensive monitoring and fail-safety mechanisms.

• Large team
  One can split development tasks between people easily. The top people can work on domain logic leaving the usual stuff to less skilled developers.
• Difficult business logic
  CQRS helps avoid mixing domain logic and infrastructural operations.
• Scalability matters
  Helps achieve great read and write performance (because queries can be optimized to do fast read operations).

Queries are a key element used for reading data. How are they helpful in the implementation process of CQRS?

1. They offer the possibility of having one table for each view. Thus, the client can simply SELECT * FROM MyViewTable.
2. There is no need for a relational database.
3. They can be scaled horizontally.

Here are some tips:

1. Use the main data store for commands.
2. Queue commands and have notifications about their execution statuses.
3. Remember there’s no need to keep the server always on since queues can hold requests.
4. After the command was executed, update the main database and query the data store concurrently.