DB retry wrapper needs to look for savepoint errors

[Kevin Benton]

If mysql triggers a deadlock error while in a nested transaction, the savepoint can be lost, which will cause a DBError from sqlalchemy that looks like the following:

2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters [req-287a245f-f5da-4126-9625-148e889b3443 tempest-NetworksTestDHCPv6-2134889417 -] DBAPIError exception wrapped from (pymysql.err.InternalError) (1305, u'SAVEPOINT sa_savepoint_1 does not exist') [SQL: u'ROLLBACK TO SAVEPOINT sa_savepoint_1']
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters Traceback (most recent call last):
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1139, in _execute_context
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters context)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 450, in do_execute
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters cursor.execute(statement, parameters)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/cursors.py", line 161, in execute
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters result = self._query(query)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/cursors.py", line 317, in _query
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters conn.query(q)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 835, in query
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters self._affected_rows = self._read_query_result(unbuffered=unbuffered)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 1019, in _read_query_result
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters result.read()
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 1302, in read
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters first_packet = self.connection._read_packet()
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 981, in _read_packet
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters packet.check_error()
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 393, in check_error
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters err.raise_mysql_exception(self._data)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/err.py", line 120, in raise_mysql_exception
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters _check_mysql_exception(errinfo)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/pymysql/err.py", line 115, in _check_mysql_exception
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters raise InternalError(errno, errorvalue)
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters InternalError: (1305, u'SAVEPOINT sa_savepoint_1 does not exist')
2016-06-08 05:15:22.609 18530 ERROR oslo_db.sqlalchemy.exc_filters
/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py:68: SAWarning: An exception has occurred during handling of a previous exception. The previous exception is:
 <class 'oslo_db.exception.DBDeadlock'> (pymysql.err.InternalError) (1213, u'Deadlock found when trying to get lock; try restarting transaction') [SQL: u'INSERT INTO ipallocations (port_id, ip_address, subnet_id, network_id) VALUES (%(port_id)s, %(ip_address)s, %(subnet_id)s, %(network_id)s)'] [parameters: {'network_id': u'bab3d364-8fff-43dd-ac4b-28baf51060e2', 'subnet_id': '0e4d20e8-9f7a-420c-947c-913e8fca99b1', 'port_id': u'856f7fe5-65b4-45f3-a3ea-e99bc2e9c1cb', 'ip_address': '2003::f816:3eff:fe5b:1efb'}]

This is a known issue with how mysql handles the savepoints on errors: https://bitbucket.org/zzzeek/sqlalchemy/issues/2696/misleading-exception-triggered-on

So we need to look for this particular exception in our retry wrapper since the real cause is likely a deadlock error.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/326927

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/326927
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=f21eed3998a793f5c40eb248469dc4245de3415a
Submitter: Jenkins
Branch: master

commit f21eed3998a793f5c40eb248469dc4245de3415a
Author: Kevin Benton <email address hidden>
Date: Tue Jun 7 14:28:59 2016 -0700

    Check for mysql SAVEPOINT error in retry decorator

    Due to lost savepoints in mysql on deadlock errors, we can get
    a non-existent savepoint error that is just masking a deadlock
    error. This patch adjusts the retry decorator to check for these
    savepoint errors as well. See the bug for more details about
    the failure.

    Closes-Bug: #1590298
    Change-Id: I29905817ad7c69986f182ff3f0d58496608cd665

[Doug Hellmann (doug-hellmann)]

This issue was fixed in the openstack/neutron 9.0.0.0b2 development milestone.