Don't override default values for oslo.db options

This change will make neutron-server use default values from oslo.db if
any of them are not overridden in config files, instead of applying its
own unique values that may be unexpected to users and operators.

It also makes our config files correct since now we don't claim wrong
values being default. (Remember the config generator was never aware of
our snowflake behaviour.)

If you wonder why we were overriding it in the first place, it was
needed back in the times when we were using db module from
oslo-incubator that has not provided proper defaults. Those times are
long gone.

Of course the change is not impact free, and operators who for some
reason want to keep the old values may need to adjust their
configuration files. Still, I believe using default values from oslo.db
is the correct thing to do long term.

We still need to set connection string for unit tests to sqlite:// since
oslo.db doesn't provide any default value for the option. It should be
fine to effectively unset default value for the option for
neutron-server since no one in production can use sqlite anyway.

This change also drops set_db_defaults function from
neutron.common.config. I have checked that there are no consumers for
the function outside the tree.

NeutronLibImpact
UpgradeImpact

Co-Authored-By: Ihar Hrachyshka <ihrachys@redhat.com>
Change-Id: Ia97d6cf24e554f7b3878dd301ae4e7e10a1c9998
Closes-Bug: #1682307

neutron/common/config.py

@@ -22,7 +22,6 @@ import sys
 from keystoneauth1 import loading as ks_loading
 from neutron_lib.api import validators
 from oslo_config import cfg
-from oslo_db import options as db_options
 from oslo_log import log as logging
 import oslo_messaging
 from oslo_middleware import cors
@@ -52,17 +51,6 @@ common_config.register_core_common_config_opts()
 oslo_messaging.set_transport_defaults(control_exchange='neutron')
 
 
-def set_db_defaults():
-    # Update the default QueuePool parameters. These can be tweaked by the
-    # conf variables - max_pool_size, max_overflow and pool_timeout
-    db_options.set_defaults(
-        cfg.CONF,
-        connection='sqlite://',
-        max_pool_size=10,
-        max_overflow=20, pool_timeout=10)
-
-set_db_defaults()
-
 NOVA_CONF_SECTION = 'nova'
 
 ks_loading.register_auth_conf_options(cfg.CONF, NOVA_CONF_SECTION)

neutron/tests/base.py

@@ -31,6 +31,7 @@ import mock
 from neutron_lib import fixture
 from oslo_concurrency.fixture import lockutils
 from oslo_config import cfg
+from oslo_db import options as db_options
 from oslo_messaging import conffixture as messaging_conffixture
 from oslo_utils import excutils
 from oslo_utils import fileutils
@@ -147,9 +148,9 @@ class DietTestCase(base.BaseTestCase):
         super(DietTestCase, self).setUp()
 
         # FIXME(amuller): this must be called in the Neutron unit tests base
-        # class to initialize the DB connection string. Moving this may cause
-        # non-deterministic failures. Bug #1489098 for more info.
-        config.set_db_defaults()
+        # class. Moving this may cause non-deterministic failures. Bug #1489098
+        # for more info.
+        db_options.set_defaults(cfg.CONF, connection='sqlite://')
 
         # Configure this first to ensure pm debugging support for setUp()
         debugger = os.environ.get('OS_POST_MORTEM_DEBUGGER')

releasenotes/notes/change-oslo-db-defaults-f94df09c30767f95.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - |
+    Previously, ``neutron-server`` was using configuration values
+    for ``oslo.db`` that were different from library defaults. Specifically, it
+    used the following values when they were not overridden in configuration
+    files: ``max_pool_size`` = 10, ``max_overflow`` = 20, ``pool_timeout`` =
+    10. In this release, ``neutron-server`` instead relies on default values
+    defined by the library itself. If you rely on old default values, you may
+    need to adjust your configuration files to explicitly set the new values.