CockroachDB Architecture

In this chapter, we'll delve into the internals of CockroachDB, a popular distributed SQL database. Not only does it support features like horizontal scaling and strong consistency, CockroachDB also touts built-in replication and seamless multi-cloud and geolocation deployment. All these features allow this SQL engine to be resilient, elastic and high-performing, living up to its name.

When discussing CockroachDB's architecture, it is often compared to a film production crew where each member plays a vital role. Just as a movie team works together to produce a film, different components of CockroachDB work in harmony to process SQL transactions.

Nodes

Imagine a movie set where each cast member represents a node. A node in CockroachDB corresponds to an individual instance of cockroach service running on a machine. These machines can be actual physical devices or virtual ones on the cloud.

This can be displayed in a cluster setup below:

cockroach start --insecure --store=node1 --listen-addr=localhost:26257 --http-host=localhost --join=localhost:26257,localhost:26258,localhost:26259 --background

Clusters

Now, let's look at a group of cast members or in CockroachDB's context, a cluster. A cluster consists of multiple nodes joined together, very much like an ensemble in a movie. Nodes in the cluster distribute data between themselves, ensuring that the load is evenly balanced and the system is resilient to failures. The cluster is the key scalable unit of CockroachDB.

Range and Raft

In our movie analogy, the script of the film can be considered as a database table. This script (or table) is divided into small parts, commonly known as a "range" in CockroachDB terminology. Instead of having one actor perform the entire script, it's divided among various actors, much in the same way a database table is split across multiple nodes for efficient processing.

CockroachDB uses the Raft consensus algorithm to keep these ranges replicated across multiple nodes. Every change to range data is logged and must pass through the Raft to ensure data remains consistent across all replicas. This is similar to how every change in a script is communicated with all cast members, to ensure everyone is on the same page.

CREATE TABLE Movies (
    ID SERIAL PRIMARY KEY,
    Name VARCHAR(255)
);

Gateways

The Director in a film can be thought of as a Gateway. The gateway nodes serve as the entry point for all client requests. When a client sends a request to CockroachDB, it arrives first at a gateway node. This node parses and analyzes the SQL, breaks it into several operations and then coordinates the execution of these operations.

INSERT INTO Movies (Name)
VALUES ('Godfather');

The SQL transaction above can be divided into different sub-tasks, including finding the appropriate range for the data, writing the data to the appropriate range, and then writing the changes to replicas of the range.

Transactions

CockroachDB provides serializable isolation for transactions, embodying the ACID principles at a global scale. This can be compared to the continuity in movies. Every transaction in CockroachDB, much like scenes in a movie, follows a strict order and never intersect with each other, ensuring that data stays consistent.

BEGIN;
INSERT INTO Movies (Name)
VALUES ('Casablanca');
COMMIT;

SQL Layer

The screenplay writer plays an analogous role to the SQL Layer in CockroachDB. Just as the screenplay lays out the scenes, dialogues and settings for the movie, the SQL layer in CockroachDB takes care of interpreting the SQL dialect. It compiles SQL to an internal, tree-like representation, transforms the tree into a plan with KV operations, and hands it off to the transaction layer for execution.

SELECT * FROM Movies WHERE Name = 'Casablanca';

Conclusion

The genius of CockroachDB lies in its symphony between the various components. From Nodes to the SQL layer, each part has a role to play to ensure it stays resilient and high-performing. And much like a movie, the seamless interworking of all these characters results in a masterpiece. By understanding these internal actors and their role in the system, you can better navigate, manage, and optimize CockroachDB to meet your specific needs. In the next chapter, we will be discussing more advanced topics related to CockroachDB's functionality.