Add deadlock retry wrapper for inital quota create

Since the initial quota record creation is using the autocommit session and
since it is creating the initial record, it will lock at the table(index)
level instead of at the record level. This can lead to a recoverable DB
Deadlock situation.
This was observed running the neutron-lbaas API tempest tests with concurrency
greater than 1.

This patch adds the oslo DB deadlock retry wrapper to this initial record
creation to allow deadlock recovery.

Change-Id: Ibbfa77f548fead3203cf081e203c5e70fe514111

octavia/db/repositories.py

@@ -21,6 +21,7 @@ reference
 import datetime
 
 from oslo_config import cfg
+from oslo_db import api as oslo_db_api
 from oslo_db import exception as db_exception
 from oslo_log import log as logging
 from oslo_utils import excutils
@@ -1307,6 +1308,12 @@ class L7PolicyRepository(BaseRepository):
 class QuotasRepository(BaseRepository):
     model_class = models.Quotas
 
+    # This is used with an autocommit session (non-lock_session)
+    # Since this is for the initial quota record creation it locks the table
+    # which can lead to recoverable deadlocks. Thus we use the deadlock
+    # retry wrapper here. This may not be appropriate for other sessions
+    # and or queries. Use with caution.
+    @oslo_db_api.wrap_db_retry(max_retries=5, retry_on_deadlock=True)
     def update(self, session, project_id, **model_kwargs):
         with session.begin(subtransactions=True):
             kwargs_quota = model_kwargs['quota']