How to resolve deadlock issues in MySQL?

Resolving deadlock issues in MySQL involves identifying the cause of the deadlock and implementing strategies to prevent or mitigate them. Deadlocks occur when two or more transactions are waiting indefinitely for each other to release locks, causing a standstill.

Here are some steps to resolve deadlock issues:

1. Identify Deadlocks: MySQL logs deadlocks in the error log or the general query log. You can use the SHOW ENGINE INNODB STATUS command to view detailed information about the last deadlock that occurred.

   Example:

   SHOW ENGINE INNODB STATUS\G;
   

2. Analyze Deadlock Information: Look for the "LATEST DETECTED DEADLOCK" section in the output. This section provides information about the transactions involved, the locks they are waiting for, and the order in which they acquired locks.

3. Optimize Queries: Deadlocks often occur due to inefficient query patterns. Review and optimize the queries involved in the deadlock to ensure they acquire locks in a consistent order.

   Example:

   -- Ensure consistent lock acquisition order
   START TRANSACTION;
   SELECT * FROM table1 WHERE id = 1 FOR UPDATE;
   SELECT * FROM table2 WHERE id = 2 FOR UPDATE;
   COMMIT;
   

4. Reduce Transaction Scope: Minimize the scope of transactions to reduce the time locks are held. This can help prevent deadlocks by reducing the likelihood of conflicts.

5. Use Shorter Transactions: Keep transactions as short as possible to minimize the time locks are held.

6. Implement Retry Logic: Implement retry logic in your application to handle deadlocks gracefully. If a deadlock occurs, the application can wait for a short period and retry the transaction.

   Example (pseudo-code):

   max_retries = 3
   for attempt in range(max_retries):
       try:
           with connection.cursor() as cursor:
               cursor.execute("START TRANSACTION;")
               cursor.execute("SELECT * FROM table1 WHERE id = 1 FOR UPDATE;")
               cursor.execute("SELECT * FROM table2 WHERE id = 2 FOR UPDATE;")
               cursor.execute("COMMIT;")
           break
       except DeadlockError:
           if attempt == max_retries - 1:
               raise
           time.sleep(0.1)
   

7. Use Read/Write Splitting: In some cases, using read/write splitting can help reduce deadlocks by offloading read operations to replicas, reducing the load on the primary database.

If you are using Tencent Cloud, you can leverage services like TencentDB for MySQL to manage your database needs. TencentDB provides features like automatic deadlock detection and resolution, as well as high availability and scalability options to help mitigate deadlock issues.