


Identifying Transactions Causing "Waiting for Table Metadata Lock" State
When attempting DDL operations on a table in MySQL version 5.5.24 but encountering "Waiting for table metadata lock" messages, it becomes crucial to determine the transaction responsible for this lock.
Solution
For MySQL versions below 5.7.3:
Execute the following command to retrieve detailed information about the state:
SHOW ENGINE INNODB STATUS \G
Locate the "TRANSACTIONS" section and identify the open transaction that is yet to be closed.
For all MySQL versions:
Retrieve information from the INFORMATION_SCHEMA tables:
All Waiting Locks:
USE INFORMATION_SCHEMA; SELECT * FROM INNODB_LOCK_WAITS;
Blocking Transactions:
SELECT * FROM INNODB_LOCKS WHERE LOCK_TRX_ID IN (SELECT BLOCKING_TRX_ID FROM INNODB_LOCK_WAITS);
OR
SELECT INNODB_LOCKS.* FROM INNODB_LOCKS JOIN INNODB_LOCK_WAITS ON (INNODB_LOCKS.LOCK_TRX_ID = INNODB_LOCK_WAITS.BLOCKING_TRX_ID);
Locks on a Specific Table:
SELECT * FROM INNODB_LOCKS WHERE LOCK_TABLE = db_name.table_name;
Waiting Transactions:
SELECT TRX_ID, TRX_REQUESTED_LOCK_ID, TRX_MYSQL_THREAD_ID, TRX_QUERY FROM INNODB_TRX WHERE TRX_STATE = 'LOCK WAIT';
Refer to MySQL Troubleshooting: What To Do When Queries Don't Work, Chapter 6, Page 96 for additional insights.
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