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[Wim De Clercq <wim.de_clercq@xxxxxxxxxxxxxxxxx>]

Public bug reported:

Only seen in Newton
Possibly related bug: https://bugs.launchpad.net/neutron/+bug/1596075

When a retriable database error occurs in a mechanism driver's
subnet_create_postcommit, you get the error saying subnet overlaps with
another subnet.

What's happening is:

1) mech driver's DB error is caught. Subnet that is created previously gets deleted in ml2plugin.
2) retry wrapper retries the create_subnet method
3) in db_base_plugin_v2#_create_subnet(self, context, subnet, subnetpool_id) method the network is fetched:
  
    network = self._get_network(context, s["network_id"])

4) This network contains the subnet that was deleted in step 1.


It is related to the backref present in Newton:
https://github.com/openstack/neutron/blob/stable/newton/neutron/db/models_v2.py#L245

which is not present in Ocata onwards. And more specifically, the
lazy='subquery' is causing it'. Leaving the lazy parameter out avoids
this issue as well.

As it currently is, the DB-retry can't work when DB errors happen in
postcommit.

** Affects: neutron
     Importance: Undecided
         Status: New


** Tags: newton

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https://bugs.launchpad.net/bugs/1699500

Title:
  network fetched from DB has deleted subnets in it during db-retry of
  subnet_create

Status in neutron:
  New

Bug description:
  Only seen in Newton
  Possibly related bug: https://bugs.launchpad.net/neutron/+bug/1596075

  When a retriable database error occurs in a mechanism driver's
  subnet_create_postcommit, you get the error saying subnet overlaps
  with another subnet.

  What's happening is:

  1) mech driver's DB error is caught. Subnet that is created previously gets deleted in ml2plugin.
  2) retry wrapper retries the create_subnet method
  3) in db_base_plugin_v2#_create_subnet(self, context, subnet, subnetpool_id) method the network is fetched:
    
      network = self._get_network(context, s["network_id"])

  4) This network contains the subnet that was deleted in step 1.

  
  It is related to the backref present in Newton:
  https://github.com/openstack/neutron/blob/stable/newton/neutron/db/models_v2.py#L245

  which is not present in Ocata onwards. And more specifically, the
  lazy='subquery' is causing it'. Leaving the lazy parameter out avoids
  this issue as well.

  As it currently is, the DB-retry can't work when DB errors happen in
  postcommit.

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