Metadata Locks

Overview

• Metadata locks (MDLs) are used to ensure consistency between DDL and DML operations. Usually, DDL operations require MDL write locks. Once an MDL lock occurs, it can have a significant impact on your database because all subsequent operations (SELECT, DML, and DDL operations) on the target table will be blocked, causing a backlog of connections.
• The system displays database MDL locks in real time. With these locks, you can quickly locate MDL problems and terminate the sessions holding MDL locks, so that blocked operations can be restored.
  

  • This feature does not support DML locks. You can view and analyze them on the InnoDB Locks page.
  • Currently, this feature is available only for MySQL 5.6 and 5.7.
  • A maximum of 1,000 records can be displayed.

Procedure

1. Log in to the DAS console.
2. On the Overview page, click Go to Intelligent O&M.
3. Select the target instance and click Details.
4. Choose Locks and Transactions > Metadata Locks.
5. Select a lock status and type, and enter a database name, table name, and session ID as needed. Then, click Query.
6. In the query result, check whether there are sessions that hold MDL locks. If yes, select the sessions as required and click Kill Session.