If you've determined that a direct upgrade from MySQL 8. x to MariaDB 10. x is not possible due to compatibility issues or other constraints, you'll need to follow a multi-step process to migrate your data. Here's a general outline of the steps you'll need to take:

1. Backup Your Data:

   • Before making any changes, ensure you have a complete backup of your MySQL 8. x database.

2. Export Data from MySQL 8. x:

   • Use tools like mysqldump to export your data from MySQL 8. x. This will create an SQL file with all your database structure and data.

3. Set Up a Temporary Database:

   • Install and configure a temporary MySQL server (compatible with both MySQL 8. x and MariaDB 10. x) where you'll import the data.

4. Import Data to Temporary Database:

   • Run the SQL file generated in step 2 to populate the temporary database.

5. Check for Compatibility Issues:

   • Verify that all data has been successfully imported and that there are no compatibility issues or errors.

6. Export Data from Temporary Database:

   • Use mysqldump again, this time from the temporary MySQL server, to create another SQL file.

7. Install MariaDB 10.x:

   • Install MariaDB 10. x on your server. Follow the official documentation for your specific operating system.

8. Import Data into MariaDB 10.x:

   • Use the SQL file generated in step 6 to populate your new MariaDB 10. x database.

9. Check Data Integrity:

   • Verify that all data has been successfully imported and that there are no integrity issues.

10. Reconfigure Applications:

    • Update your applications, scripts, and configurations to point to the new MariaDB 10. x database.

11. Test Applications:

    • Thoroughly test all your applications to ensure they function correctly with the new database.

12. Performance Tuning (if necessary):

    • Adjust MariaDB configurations to optimize performance based on your specific workload.

13. Regular Backups:

    • Set up regular backups for your new MariaDB 10. x database to ensure data safety.

Remember to consult the official documentation for both MySQL and MariaDB during this process. Also, consider consulting with a database administrator or expert if you're not comfortable with these steps, as database migrations can be complex and may have unforeseen challenges.