MySQL 8.x Setup and Configuration#

MySQL 8.x is the current production series. It introduced caching_sha2_password as the default auth plugin, CTEs, window functions, and a redesigned data dictionary. Getting it installed is straightforward; getting it configured correctly for production takes more thought.

Installation#

Package Managers#

On Ubuntu/Debian, the MySQL APT repository gives you the latest 8.x:

# Add the MySQL APT repo
wget https://dev.mysql.com/get/mysql-apt-config_0.8.30-1_all.deb
sudo dpkg -i mysql-apt-config_0.8.30-1_all.deb
sudo apt update
sudo apt install mysql-server

On RHEL/Rocky/AlmaLinux:

MySQL Backup and Recovery#

A backup that has never been restored is not a backup. This guide covers the tools, when to use each, and how to verify your backups work.

Logical vs Physical Backups#

Logical backups export SQL statements. Portable across versions but slow for large databases. Physical backups copy raw InnoDB data files. Fast but tied to the same MySQL version. Physical backups are essential once your database exceeds a few hundred gigabytes.

MySQL Debugging: Common Problems and Solutions#

When MySQL breaks, it falls into a handful of failure modes. Here are the diagnostic workflows, in order of frequency.

Access Denied Errors#

Access denied for user 'appuser'@'10.0.1.5' (using password: YES) means wrong password, user does not exist for that host, or missing privileges.

Diagnosis:

-- 1. Does the user exist for that host?
SELECT user, host, plugin FROM mysql.user WHERE user = 'appuser';
-- MySQL matches user+host pairs. 'appuser'@'localhost' != 'appuser'@'%'.

-- 2. Check grants
SHOW GRANTS FOR 'appuser'@'%';

-- 3. Auth plugin mismatch? Old clients can't handle caching_sha2_password:
ALTER USER 'appuser'@'%' IDENTIFIED WITH mysql_native_password BY 'password';

To reset a lost root password:

MySQL Performance Tuning#

Performance tuning comes down to three things: making queries touch fewer rows (indexes), keeping hot data in memory (buffer pool), and finding the slow queries (slow query log, Performance Schema).

Reading EXPLAIN Output#

EXPLAIN shows MySQL’s query execution plan. Always use EXPLAIN ANALYZE (MySQL 8.0.18+) for actual runtime stats, not just estimates.

EXPLAIN ANALYZE
SELECT u.name, COUNT(o.id) as order_count
FROM users u
JOIN orders o ON o.user_id = u.id
WHERE u.created_at > '2025-01-01'
GROUP BY u.id;

Key columns: