Configuring innodb_read_io_threads and innodb_write_io_threads in MySQL 8 is a crucial part of tuning InnoDB performance, especially for systems dealing with heavy read/write operations. These settings control the number of I/O threads for read and write operations within InnoDB, which directly impacts how efficiently MySQL handles I/O-bound workloads.

General Recommendations

1. Understanding the Default Values

• By default, both innodb_read_io_threads and innodb_write_io_threads are set to 4. This is usually sufficient for most applications, but for high I/O systems, adjustments may be needed.

2. Adjusting Values Based on Workload

• Read-Intensive Workloads: If your workload is read-intensive, you might benefit from increasing innodb_read_io_threads.
• Write-Intensive Workloads: Conversely, for write-heavy databases, increasing innodb_write_io_threads can improve performance.

3. Consider Hardware Capabilities

• Disk Type: SSDs can handle more I/O threads efficiently compared to HDDs. If using SSDs, you can typically set higher values.
• CPU Cores: Ensure your server has enough CPU cores to handle the increased number of threads. Each thread will consume CPU resources.

4. Typical Range for Configuration

• Values typically range from 4 to 64, depending on the system’s capacity and workload. Avoid setting too high, as it can lead to increased context switching and CPU overhead.

5. Monitor Performance

• After adjusting these settings, monitor your system’s performance. Look for improvements in I/O throughput and overall query response times.
• Use tools like iostat, vmstat, and MySQL's SHOW ENGINE INNODB STATUS to monitor I/O activity.

6. Incremental Changes

• Make incremental changes rather than large adjustments. For example, you might increase the value from 4 to 8, then to 16 if needed, monitoring the impact each time.

7. Balancing Read and Write Threads

• Ensure a balance between read and write threads. Over-allocating to one can starve the other, leading to performance degradation.

8. Operating System Limits

• Be aware of your operating system’s limits on threads and file descriptors. High numbers of I/O threads can increase the number of file descriptors needed.

9. Server Workload and Configuration

• Tailor these settings to your specific server workload and configuration. What works for one environment may not be optimal for another.

10. Updating Configuration

• To change these settings, update your MySQL configuration file (typically my.cnf or my.ini):

  [mysqld]
  innodb_read_io_threads = 8
  innodb_write_io_threads = 8
  
  

• Restart the MySQL server for changes to take effect.

Conclusion

The optimal settings for innodb_read_io_threads and innodb_write_io_threads depend on your specific system architecture and workload. It's crucial to test different configurations and closely monitor the impact on system performance to find the best settings for your environment. Remember, changing these settings can have significant impacts, so it's always best to make such adjustments in a controlled, testing environment before deploying to production.