sqlalchemy force all connections to close mysql

Question

We use sqlalchemy in some complicated unit tests. At the end of each test, we tear down the database entirely using drop_all. Now and then, someone forgets to close a session embedded deep inside a unit test. We then have to spend a fair amount of time trying to figure out just what is going wrong, and ultimately to close the sqlalchemy session.

We want a want to reliably way to force all the connections to the database to close. We have tried session.close_all(), but this did not do what I describe.

Edit: Below is the mysql processlist we see when the process hangs attempting to drop the database. Presumably Id 285 is the offending process:

+-----+------+-----------------+----------+---------+------+---------------------------------+------------------------------+
| Id  | User | Host            | db       | Command | Time | State                           | Info                         |
+-----+------+-----------------+----------+---------+------+---------------------------------+------------------------------+
| 172 | root | localhost       | mydb     | Query   |    0 | init                            | show processlist             |
| 285 | root | localhost:47147 | mydb     | Sleep   |    6 |                                 | NULL                         |
| 289 | root | localhost:47152 | mydb     | Query   |    5 | Waiting for table metadata lock | DROP TABLE `mytable`         |
+-----+------+-----------------+----------+---------+------+---------------------------------+------------------------------+

Edit: Per request, I am also including the transaction log:

------------
TRANSACTIONS
------------
Trx id counter 1144929
Purge done for trx's n:o < 1144827 undo n:o < 0 state: running but idle
History list length 398
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started
MySQL thread id 37, OS thread handle 0x8f46bb40, query id 776 localhost root init
show engine innodb status
---TRANSACTION 0, not started
MySQL thread id 45, OS thread handle 0x8f2ceb40, query id 774 localhost 127.0.0.1 root Waiting for table metadata lock
DROP TABLE `mytable`
---TRANSACTION 1144823, ACTIVE 12 sec
MySQL thread id 41, OS thread handle 0x8f2ffb40, query id 595 localhost 127.0.0.1 root cleaning up
Trx read view will not see trx with id >= 1144824, sees < 1144824

Answer 1

In flask, this should do the trick:

@app.teardown_appcontext
def teardown_db(exception):
    db.session.commit()
    db.session.close()