How to Troubleshoot 'Lock wait timeout exceeded' Errors in MySQL?

How to debug "Lock wait timeout exceeded on MySQL"?

In the error logs, when a "Lock wait timeout exceeded" error occurs, it indicates that a query is attempting to modify data in an InnoDB table and encountering a lock conflict. To debug this issue, you can follow these steps:

1. Identify the Query: Determine which query is causing the lock timeout by checking the queries being executed at the time of the error.
2. Locate the Table(s) Involved: Since locks are applied at the table level in InnoDB, identify the table(s) that are being accessed by the query.
3. Retrieve Lock Information: To gather detailed information about the locks being held, execute the "SHOW ENGINE INNODB STATUSG" command.
4. Analyze Lock Status: Within the output of the command, search for "LOCK" sections that indicate the tables affected by locks. You will find information about the threads involved in the locking process, the specific locks being held, and the transactions that have acquired the locks.

5. Resolve Lock Conflicts: Once you have identified the affected tables and the nature of the lock conflicts, you have two options:

   • Increase the Lock Wait Timeout: Increase the innodb_lock_wait_timeout configuration variable to allow more time for lock resolution. This can be done temporarily or permanently based on your requirements.
   • Identify and Kill Blocking Query: If the lock conflict is caused by a problematic query, such as a long-running transaction or a deadlock, you may need to identify and kill the blocking query to release the lock. You can use tools like "pt-kill" to terminate specific processes.

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