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Upgrading MySQL from version 5.7 to 8.0 is a significant step as MySQL 8.0 introduces several new features and improvements, but it also includes breaking changes and requires careful planning. Below is a step-by-step guide for upgrading MySQL 5.7 to 8.0.

1. Backup Your Data

Before starting the upgrade process, take a full backup of your databases to avoid any potential data loss in case something goes wrong.

• Use mysqldump to create a backup:

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mysqldump -u root -p –all-databases –routines –triggers –events –single-transaction > all_databases_backup.sql

• Alternatively, you can create a backup using mysqlbackup or other backup tools.

2. Review MySQL 8.0 Changes

MySQL 8.0 comes with many changes (e.g., new features, deprecations, and removed features). Review the MySQL 8.0 Release Notes to understand the changes.

• Check for incompatible changes, such as:
  • Removal of the query_cache feature.
  • Changes to the default authentication plugin (caching_sha2_password).
  • Alterations to the default character set (from latin1 to utf8mb4).
  • Reserved keywords that may affect your queries or schemas.

3. Check MySQL 5.7 Compatibility with MySQL 8.0

Run the MySQL Upgrade Checker Tool to check for potential issues and compatibility:

• Download and install the mysql_upgrade_checker tool from MySQL’s GitHub or use the following steps:

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wget https://dev.mysql.com/get/Downloads/Tools/mysql-compatibility-checker/mysql-upgrade-checker-1.0.tar.gz

tar -xvf mysql-upgrade-checker-1.0.tar.gz

cd mysql-upgrade-checker-1.0

./mysql_upgrade_checker –mysql5_7 /path/to/mysql57 –mysql8_0 /path/to/mysql80

• Alternative Method: You can also use mysql_upgrade on 5.7 to check for potential issues:

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mysql_upgrade -u root -p

4. Stop MySQL Server

Stop the MySQL 5.7 server before upgrading:

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sudo systemctl stop mysql

5. Install MySQL 8.0

The method for upgrading depends on your operating system. Below are instructions for the most common systems.

For Ubuntu/Debian:

1. Update APT Repositories: If you haven’t already, add the MySQL APT repository to your system.

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wget https://dev.mysql.com/get/mysql-apt-config_0.8.17-1_all.deb

sudo dpkg -i mysql-apt-config_0.8.17-1_all.deb

sudo apt-get update

1. Install MySQL 8.0:

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sudo apt-get install mysql-server=8.0.XX-1debian10

Replace 8.0.XX-1debian10 with the appropriate MySQL 8.0 version for your distribution.

For CentOS/RHEL:

1. Add MySQL Repository:

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wget https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm

sudo rpm -ivh mysql80-community-release-el7-3.noarch.rpm

1. Install MySQL 8.0:

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sudo yum install mysql-community-server

1. Enable and Start MySQL 8.0:

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sudo systemctl enable mysqld

sudo systemctl start mysqld

6. Upgrade the Data Directory

MySQL 8.0 may require an upgrade to your data directory. When you first start MySQL 8.0, it will attempt to upgrade your data format.

• Start MySQL 8.0:

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sudo systemctl start mysql

• MySQL will automatically upgrade the system tables and the data directory. If needed, you can manually run the mysql_upgrade tool:

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sudo mysql_upgrade -u root -p

This will upgrade your database to MySQL 8.0, including checking and upgrading system tables and repairing any issues with your data.

7. Review and Update Configuration Files

After upgrading, verify and update your MySQL configuration files (my.cnf or my.ini) to ensure compatibility with MySQL 8.0.

1. Check for Deprecated or Removed Options:
   • Remove any deprecated settings like query_cache_size or lower_case_table_names (depending on your environment).
   • MySQL 8.0 does not support the query_cache feature, so make sure it’s disabled.
2. Update Authentication Plugin: If you are using the default MySQL authentication plugin (caching_sha2_password), you may need to update the configuration to allow compatibility with MySQL 5.7 clients:

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[mysqld]

default_authentication_plugin=caching_sha2_password

1. Adjust Other Settings: Review MySQL 8.0’s new settings and make adjustments accordingly.

8. Test the Upgrade

Once the upgrade is complete:

1. Verify the MySQL Version: Check the MySQL version to ensure the upgrade was successful:

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mysql -u root -p -e “SELECT VERSION();”

1. Check Logs: Review the MySQL error log for any issues or warnings:

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tail -f /var/log/mysql/error.log

1. Test Your Applications: Run your applications and perform functional testing to ensure everything is working as expected.
2. Check Database Integrity: Verify that all your databases are intact:

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mysqlcheck -u root -p –all-databases

9. Post-Upgrade Steps

• Rebuild Indexes: Some indexes may need to be rebuilt after an upgrade.
• Enable or Optimize New Features: MySQL 8.0 introduces several new features such as window functions, common table expressions (CTEs), and better JSON support. Consider enabling or optimizing these features in your environment.

10. Rollback Plan

If the upgrade fails or something goes wrong, use your backup to roll back to MySQL 5.7.

1. Stop MySQL 8.0:

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sudo systemctl stop mysql

1. Restore the backup:

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mysql -u root -p < all_databases_backup.sql

1. Start MySQL 5.7 again:

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sudo systemctl start mysql

Important Notes:

• In-Place Upgrade vs Fresh Install: You can choose between performing an in-place upgrade or setting up MySQL 8.0 on a fresh server and migrating your data.
• Version-Specific Features: Be aware of any features that might have been deprecated or modified between MySQL 5.7 and 8.0, such as character sets, authentication plugins, and query optimizations.
• Testing: Always test in a staging environment before performing the upgrade in production to minimize risks.