Data Storage and Replication

As mentioned earlier, CockroachDB stores and organizes data in a way that enables efficient distribution and replication across nodes, ensuring both high availability and strong consistency with the KV layer. The 64MB ranges provide the basic unit for data distribution and replication within CockroachDB.

Each range in CockroachDB is replicated across multiple nodes by the Raft consensus algorithm. By default, CockroachDB creates three replicas of each range, but this replication factor can be adjusted according to the desired level of fault tolerance and performance. Replicas are stored on different nodes, ensuring high availability and fault tolerance in the face of node failures or network partitions.

To illustrate the process of data replication, assume you have a three-node CockroachDB cluster and a books table with the schema defined earlier. When you insert a new book into the table:

INSERT INTO books (title, author, publication_date, price) VALUES
('Moby-Dick', 'Herman Melville', '1851-10-18', 19.99);

CockroachDB first determines by its key the range to which the new data belongs. Once the appropriate range is identified, the write operation is forwarded to the Raft leader for that range. The leader then replicates the operation to the other replicas in the Raft group by appending it to their Raft logs.

When a majority of the replicas acknowledge that they have successfully applied the operation to their logs, the Raft leader commits the operation and informs the other replicas. At this point, the write operation is considered successful, and the new data is consistently stored across a majority of the replicas.

CockroachDB continuously monitors the distribution of ranges and their replicas across nodes. If it detects an imbalance, it automatically rebalances the data by moving ranges and replicas to different nodes. This process helps ensure that no single node becomes a bottleneck and that the cluster maintains optimal performance. The system also provides mechanisms for controlling the distribution of data on the basis of geographic location or other criteria. For example, you can use partitioning and replication zone configurations to control how data is distributed across nodes and regions. This allows you to optimize data locality and performance for geographically distributed applications.

Deployment

One of the key strengths of CockroachDB is its ability to scale horizontally and adapt to the changing needs of your application by deploying a multinode CockroachDB cluster and scaling by adding more nodes.

To start, assume you have three machines on which you'd like to deploy a CockroachDB cluster. On each machine, install the CockroachDB binary. To do so, download the most recent version from the Releases page [3] by following the instructions on the official website [4].

Next, initialize the first node in your cluster on the first machine with the command

cockroach start --insecure --advertise-addr=<node1_address> --join=<node1_address>,<node2_address>,<node3_address> --background

This command starts the first node, specifies its address (--advertise-addr), and provides a list of all the nodes in the cluster with --join. The --background flag tells CockroachDB to run the process in the background.

Now, start the second and third nodes on the respective machines with similar commands:

cockroach start --insecure --advertise-addr=<node2_address>  --join=<node1_address>,<node2_address>,<node3_address> --background
cockroach start --insecure --advertise-addr=<node3_address> --join=<node1_address>,<node2_address>,<node3_address> --background

Once all three nodes are running, you'll have a fully functional, three-node CockroachDB cluster. You can interact with the cluster from the built-in SQL shell or any PostgreSQL-compatible client. For example, you can connect to the cluster with the command

cockroach sql --insecure --host=<node1_address>

Now, assume your application is growing, and you want to scale your CockroachDB cluster to handle the increased workload. To do so, simply add more nodes to the cluster. For example, to add a fourth node, start the CockroachDB process on a new machine with the command

cockroach start --insecure--advertise-addr=<node4_address> --join=<node1_address>,<node2_address>,<node3_address> --background

As soon as the new node joins the cluster, CockroachDB automatically rebalances the data and distributes the load across all the nodes, ensuring optimal performance. You can continue to add more nodes as needed to accommodate your application's growth. In addition to scaling out by adding more nodes, you can also scale CockroachDB by partitioning your data according to specific criteria, such as geographic location or user groups. This method allows you to optimize data locality and performance for specific use cases.

Backing Up and Restoring

Ensuring the safety and durability of your data is crucial for any database system. CockroachDB provides built-in backup and restore functionality to help you protect your data and recover from disasters. In this section, I'll use code examples to show how to create backups, restore data from backups, and explore incremental backups.

To create a backup of a CockroachDB database, you can use the BACKUP statement. The following example creates a full backup of the mydb database and stores it in a local directory:

BACKUP DATABASE mydb TO 'file:///backups/mydb/full';

You can also store the backup in cloud storage services like Amazon S3, Google Cloud Storage, or Azure Blob Storage. For example, to store the backup in an S3 bucket, you would use a command like

BACKUP DATABASE mydb TO 's3://my-bucket/backups/mydb/full' WITH AWS_ACCESS_KEY_ID='<your_aws_access_key>', AWS_SECRET_ACCESS_KEY='<your_aws_secret_key>';

Remember to replace <your_aws_access_key> and <your_aws_secret_key> with your actual AWS credentials.

To restore a database from a backup, you can use the RESTORE statement. The following example restores the mydb database from the local backup created earlier:

RESTORE DATABASE mydb FROM 'file:///backups/mydb/full';

Similarly, to restore the database from an S3 backup, you would use a command like

RESTORE DATABASE mydb FROM 's3://my-bucket/backups/mydb/full' WITH AWS_ACCESS_KEY_ID='<your_aws_access_key>', AWS_SECRET_ACCESS_KEY='<your_aws_secret_key>';

CockroachDB also supports incremental backups, which allow you to create backups of only the data that has changed since the last backup. To create an incremental backup, you need to specify the base backup and the location where the incremental backup will be stored. For example, the following command creates an incremental backup of the mydb database on the basis of the previous full backup and stores it in a local directory:

BACKUP DATABASE mydb TO 'file:///backups/mydb/incremental' INCREMENTAL FROM 'file:///backups/mydb/full';

To restore a database from a series of incremental backups, you can use the RESTORE statement

RESTORE DATABASE mydb FROM 'file:///backups/mydb/full', 'file:///backups/mydb/incremental';

with the list of backup locations in chronological order.