Sysiq is an interactive platform to learn system design by building and simulating real architectures in the browser.

How does the system design simulator work?

The simulator lets you drag and drop components like load balancers, databases, and caches, and see how traffic flows, fails, or scales in real-time.

Is Sysiq free to use?

Sysiq offers a free tier to learn the basics, with premium modules available for deep-dives into advanced system architecture and scaling.

Understanding the CAP Theorem in Practice

The CAP theorem is a fundamental concept in distributed systems. It states that a distributed data store can only guarantee two out of the following three characteristics:

1. Consistency: Every read receives the most recent write or an error. 2. Availability: Every request receives a (non-error) response, without the guarantee that it contains the most recent write. 3. Partition Tolerance: The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes.

The Reality of Networks

Because networks are unreliable, network partitions *will* happen. Therefore, you must always choose Partition Tolerance (P). The real choice is between Consistency (C) and Availability (A).

CP Systems (Consistency & Partition Tolerance): If a partition occurs, the system will return an error or time out rather than returning stale data. Examples: MongoDB, HBase.

AP Systems (Availability & Partition Tolerance): The system will always return a response, even if it's stale data. Examples: Cassandra, DynamoDB.

Choosing the right database depends entirely on your application's business requirements. A banking app might need CP, while a social media feed is perfectly fine with AP.