How to Identify the Transaction Holding the \"Waiting for Table Metadata Lock\" in MySQL?

Locating the Transaction Causing "Waiting for Table Metadata Lock" State

In MySQL, encountering a "Waiting for table metadata lock" message during DDL operations indicates a lock held by another transaction. To determine the culprit transaction, consider the following methods:

MySQL Version < 5.7.3

• SHOW ENGINE INNODB STATUS G: This command displays the "TRANSACTIONS" section, listing open transactions.

INFORMATION_SCHEMA Tables

• SELECT * FROM INNODB_LOCK_WAITS: Retrieves information about all lock waits.
• SELECT * FROM INNODB_LOCKS WHERE LOCK_TRX_ID IN (SELECT BLOCKING_TRX_ID FROM INNODB_LOCK_WAITS): Identifies blocking transactions.
• SELECT * FROM INNODB_LOCKS INNER JOIN INNODB_LOCK_WAITS ON (INNODB_LOCKS.LOCK_TRX_ID = INNODB_LOCK_WAITS.BLOCKING_TRX_ID): Lists the same information as the previous query.
• SELECT * FROM INNODB_LOCKS WHERE LOCK_TABLE = db_name.table_name: Locates locks on a specific table.
• SELECT TRX_ID, TRX_REQUESTED_LOCK_ID, TRX_MYSQL_THREAD_ID, TRX_QUERY FROM INNODB_TRX WHERE TRX_STATE = 'LOCK WAIT': Lists transactions waiting for locks.

Reference:

• MySQL Troubleshooting: What To Do When Queries Don't Work, Chapter 6 - Page 96

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