High Availability in NewSQL

1. Introduction

High availability (HA) is a critical requirement for NewSQL databases, which combine the scalability of NoSQL with the ACID transactions of traditional SQL databases. This lesson covers the key concepts and techniques for achieving high availability in NewSQL systems.

2. Key Concepts

2.1 What is High Availability?

High availability refers to systems that are reliable and operational for a high percentage of time, minimizing downtime and ensuring continuous access to data.

2.2 NewSQL Overview

NewSQL databases are designed to provide the scalability of NoSQL systems while maintaining the consistency and reliability of traditional SQL databases. They use distributed architectures to ensure data is available across multiple nodes.

3. High Availability Techniques

3.1 Data Replication

Data replication involves copying data across multiple nodes to ensure that if one node fails, others can serve the data. There are two types of replication:

Synchronous Replication
Asynchronous Replication

Example of asynchronous replication implementation in a NewSQL database:


                CREATE TABLE users (
                    id INT PRIMARY KEY,
                    name VARCHAR(100)
                );

                INSERT INTO users (id, name) VALUES (1, 'Alice');
                -- Asynchronous replication setup
                SET GLOBAL async_replication = ON;

3.2 Load Balancing

Load balancing distributes client requests evenly across multiple database instances to prevent any single instance from becoming a bottleneck.

Example of load balancing configuration:


                load_balancer = {
                    "type": "round-robin",
                    "servers": [
                        "db1.example.com",
                        "db2.example.com",
                        "db3.example.com"
                    ]
                }

3.3 Failover Mechanisms

Failover mechanisms automatically switch to a standby database in the event of a failure, ensuring minimal disruption.

Example of a failover script:


                if ! ping -c 1 db_primary; then
                    echo "Failover to standby database"
                    switch_to_standby_db
                fi

4. Best Practices

Regularly test failover mechanisms to ensure they work as expected.
Implement monitoring tools to detect node failures promptly.
Use automated backups to recover data in case of catastrophic failures.
Document your high availability architecture and procedures.

5. FAQ

What is the main goal of high availability?

The main goal of high availability is to ensure that a system remains operational and accessible with minimal downtime.

How does NewSQL achieve high availability?

NewSQL achieves high availability through distributed architectures, data replication, load balancing, and automated failover mechanisms.

What are the differences between synchronous and asynchronous replication?

Synchronous replication ensures that data is written to all nodes before confirming the transaction, while asynchronous replication allows confirmation after writing to the primary node, which can result in data loss in case of a failure.