[mysql] How do I find which transaction is causing a "Waiting for table metadata lock" state?

I am trying to perform some DDL on a table and SHOW PROCESSLIST results in a " Waiting for table metadata lock " message.

How can I find out which transaction is not yet closed?

I'm using MySQL v5.5.24.

I had a similar issue with Datagrip and none of these solutions worked.

Once I restarted the Datagrip Client it was no longer an issue and I could drop tables again.

mysql 5.7 exposes metadata lock information through the performance_schema.metadata_locks table.

Documentation here

If you cannot find the process locking the table (cause it is alreay dead), it may be a thread still cleaning up like this

section TRANSACTION of

show engine innodb status;

at the end

---TRANSACTION 1135701157, ACTIVE 6768 sec
MySQL thread id 5208136, OS thread handle 0x7f2982e91700, query id 882213399 xxxIPxxx 82.235.36.49 my_user cleaning up

as mentionned in a comment in Clear transaction deadlock?

you can try killing the transaction thread directly, here with

 KILL 5208136;

worked for me.