Configuring MySQL 8's Performance Schema to troubleshoot disk I/O performance involves enabling specific instruments and consumers within the schema. Performance Schema, when properly configured, can provide detailed insights into file I/O operations, which are crucial for diagnosing performance issues related to disk I/O. Here’s how to set it up:

1. Enable Performance Schema

First, ensure that the Performance Schema is enabled in your MySQL server:

[mysqld]
performance_schema = ON

This line should be in your MySQL configuration file (my.cnf or my.ini). If it's not present, add it under the [mysqld] section and restart your MySQL server.

2. Enable File I/O Instruments

By default, not all instruments are enabled in the Performance Schema. Enable file I/O-related instruments:

1. Connect to MySQL:

   mysql -u root -p
   
   

2. Enable File I/O Instruments:

   UPDATE performance_schema.setup_instruments
   SET ENABLED = 'YES', TIMED = 'YES'
   WHERE NAME LIKE 'wait/io/file/%';
   
   

3. Enable the File I/O Consumer

Enable the consumer for file I/O events:

UPDATE performance_schema.setup_consumers
SET ENABLED = 'YES'
WHERE NAME = 'events_waits_history_long';

4. Monitor File I/O

After enabling the necessary instruments and consumers, you can start monitoring file I/O events. Query the Performance Schema to get file I/O statistics:

SELECT EVENT_NAME, COUNT_STAR, SUM_TIMER_WAIT
FROM performance_schema.events_waits_summary_global_by_event_name
WHERE EVENT_NAME LIKE 'wait/io/file/%'
ORDER BY SUM_TIMER_WAIT DESC;

This query provides information on the type and count of file I/O events, along with the total wait time, helping identify any potential I/O bottlenecks.

5. Analyze Specific File I/O Operations

To get more detailed information on specific file I/O operations, query the events_waits_history_long table:

SELECT THREAD_ID, EVENT_NAME, TIMER_START, TIMER_END, TIMER_WAIT, NUMBER_OF_BYTES, OBJECT_NAME
FROM performance_schema.events_waits_history_long
WHERE EVENT_NAME LIKE 'wait/io/file/%';

This query shows individual file I/O events, including the thread responsible, duration, and the file involved.

6. Regular Monitoring and Analysis

• Regularly monitor the file I/O statistics to understand your disk I/O patterns.
• Compare the results over time to identify changes in I/O performance.

7. Additional Considerations

• Disk Hardware and Configuration: Performance Schema helps identify I/O issues, but resolving them may require hardware changes (like moving to SSDs) or system configuration adjustments.
• Database Optimization: High I/O might also indicate a need for query optimization, indexing, or schema changes.
• OS-Level Monitoring: Complement MySQL monitoring with OS-level tools (like iostat, vmstat, htop) for a comprehensive view of I/O performance.

Conclusion

Configuring the Performance Schema in MySQL 8 for disk I/O troubleshooting allows you to monitor and analyze file I/O operations, which is crucial for identifying and resolving performance bottlenecks. Regular monitoring and analysis, combined with systemic optimization and possibly hardware upgrades, are key to maintaining optimal I/O performance.