Troubleshooting blocks in MySQL 8 - shiviyer/Blogs GitHub Wiki

Troubleshooting blocks, often manifested as lock waits or deadlocks in MySQL 8, requires a systematic approach to identify and resolve the issues causing these blocks. Locks are essential for database consistency but can lead to performance issues if not properly managed. Here's a guide to troubleshooting blocks in MySQL 8:

1. Identify Blocking Queries

  • Use Performance Schema: The Performance Schema in MySQL 8 can help identify blocking queries. Tables like events_waits_current and performance_schema.data_locks are useful.

    SELECT * FROM performance_schema.data_locks WHERE LOCK_STATUS = 'WAITING';

  • Information Schema: Check the INFORMATION_SCHEMA.INNODB_LOCKS and INNODB_LOCK_WAITS tables to find which transactions are waiting for locks.

2. Analyze Deadlocks

  • Deadlock Logs: Enable the innodb_print_all_deadlocks option in your MySQL configuration to log all deadlocks to the MySQL error log for analysis.

    [mysqld]
innodb_print_all_deadlocks=ON

  • Deadlock Detection: MySQL automatically detects deadlocks and rolls back one of the transactions. Analyze the deadlock logs to understand what caused it.

3. Monitoring Tools

  • Use Tools: Tools like SHOW ENGINE INNODB STATUS;, Workbench, or third-party tools like Percona Monitoring and Management (PMM) can provide insights into lock waits and deadlocks.

4. Optimize Query Performance

  • Indexing: Ensure that your queries are properly indexed. Missing indexes can lead to full table scans, increasing the likelihood of locks.
  • Query Optimization: Optimize long-running queries as they can hold locks for extended periods, causing blocks.

5. Adjust Isolation Levels

  • Isolation Levels: Sometimes, adjusting the transaction isolation level can reduce locking conflicts. For instance, switching from REPEATABLE READ to READ COMMITTED might help, but understand the implications on consistency.

    SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

6. Reduce Transaction Sizes

  • Smaller Transactions: Break large transactions into smaller ones to reduce the time locks are held.

7. Fine-Tune InnoDB Locking

  • InnoDB Locks: Configure InnoDB locking settings like innodb_lock_wait_timeout to control how long a transaction waits for a lock before timing out.

    SET GLOBAL innodb_lock_wait_timeout = X;  -- X is the timeout in seconds

8. Use Concurrency Control

  • Locking Hints: Use locking hints like FOR UPDATE or LOCK IN SHARE MODE in SELECT statements to control locking behavior.

9. Application-Level Changes

  • Review Application Logic: Sometimes, the way the application accesses the database can cause locks. Review and optimize application logic and database access patterns.

10. Regular Health Checks

  • Proactive Monitoring: Regularly monitor your database’s performance and look for signs of locking issues.

Conclusion

Troubleshooting blocks in MySQL 8 involves identifying the root causes, whether they are inefficient queries, poor indexing, or inappropriate transaction isolation levels. Regular monitoring and proactive optimization of queries and database settings can significantly reduce the occurrence of blocks, leading to a smoother, more efficient database operation.

Source: https://minervadb.xyz/troubleshooting-innodb-io-subsystem-reads-tips-and-tricks-for-mysql-performance-optimization/