Merge "Reset the cell cache for database access in Service" into stable/queens
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commit
779e88d5f2
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@ -37,9 +37,6 @@ from nova import policy
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from nova import utils
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LOG = logging.getLogger(__name__)
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# TODO(melwitt): This cache should be cleared whenever WSGIService receives a
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# SIGHUP and periodically based on an expiration time. Currently, none of the
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# cell caches are purged, so neither is this one, for now.
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CELL_CACHE = {}
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# NOTE(melwitt): Used for the scatter-gather utility to indicate we timed out
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# waiting for a result from a cell.
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@ -152,6 +152,20 @@ class Service(service.Service):
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This includes starting an RPC service, initializing
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periodic tasks, etc.
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"""
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# NOTE(melwitt): Clear the cell cache holding database transaction
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# context manager objects. We do this to ensure we create new internal
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# oslo.db locks to avoid a situation where a child process receives an
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# already locked oslo.db lock when it is forked. When a child process
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# inherits a locked oslo.db lock, database accesses through that
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# transaction context manager will never be able to acquire the lock
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# and requests will fail with CellTimeout errors.
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# See https://bugs.python.org/issue6721 for more information.
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# With python 3.7, it would be possible for oslo.db to make use of the
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# os.register_at_fork() method to reinitialize its lock. Until we
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# require python 3.7 as a mininum version, we must handle the situation
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# outside of oslo.db.
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context.CELL_CACHE = {}
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assert_eventlet_uses_monotonic_clock()
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verstr = version.version_string_with_package()
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@ -307,6 +321,8 @@ class Service(service.Service):
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def reset(self):
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"""reset the service."""
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self.manager.reset()
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# Reset the cell cache that holds database transaction context managers
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context.CELL_CACHE = {}
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class WSGIService(service.Service):
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@ -357,13 +373,18 @@ class WSGIService(service.Service):
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setup_profiler(name, self.host)
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def reset(self):
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"""Reset server greenpool size to default and service version cache.
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"""Reset the following:
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* server greenpool size to default
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* service version cache
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* cell cache holding database transaction context managers
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:returns: None
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"""
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self.server.reset()
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service_obj.Service.clear_min_version_cache()
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context.CELL_CACHE = {}
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def _get_manager(self):
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"""Initialize a Manager object appropriate for this service.
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@ -391,6 +412,20 @@ class WSGIService(service.Service):
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:returns: None
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"""
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# NOTE(melwitt): Clear the cell cache holding database transaction
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# context manager objects. We do this to ensure we create new internal
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# oslo.db locks to avoid a situation where a child process receives an
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# already locked oslo.db lock when it is forked. When a child process
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# inherits a locked oslo.db lock, database accesses through that
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# transaction context manager will never be able to acquire the lock
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# and requests will fail with CellTimeout errors.
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# See https://bugs.python.org/issue6721 for more information.
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# With python 3.7, it would be possible for oslo.db to make use of the
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# os.register_at_fork() method to reinitialize its lock. Until we
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# require python 3.7 as a mininum version, we must handle the situation
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# outside of oslo.db.
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context.CELL_CACHE = {}
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ctxt = context.get_admin_context()
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service_ref = objects.Service.get_by_host_and_binary(ctxt, self.host,
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self.binary)
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@ -0,0 +1,103 @@
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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from nova import context as nova_context
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from nova import test
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from nova.tests import fixtures as nova_fixtures
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from nova.tests.functional import integrated_helpers
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from nova.tests.unit import fake_network
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from nova.tests.unit.image import fake as fake_image
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from nova.tests.unit import policy_fixture
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class ServiceTestCase(test.TestCase,
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integrated_helpers.InstanceHelperMixin):
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"""Contains scenarios for testing services.
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"""
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def setUp(self):
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super(ServiceTestCase, self).setUp()
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# Use the standard fixtures.
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self.useFixture(policy_fixture.RealPolicyFixture())
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self.useFixture(nova_fixtures.NeutronFixture(self))
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self.useFixture(nova_fixtures.PlacementFixture())
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fake_image.stub_out_image_service(self)
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self.addCleanup(fake_image.FakeImageService_reset)
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fake_network.set_stub_network_methods(self)
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# Start nova controller services.
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self.api = self.useFixture(nova_fixtures.OSAPIFixture(
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api_version='v2.1')).api
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self.start_service('conductor')
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self.scheduler = self.start_service('scheduler')
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# Our OSAPIFixture does not use a WSGIService, so just use the metadata
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# server fixture (which uses WSGIService) for testing.
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self.metadata = self.useFixture(
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nova_fixtures.OSMetadataServer()).metadata
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# Start one compute service.
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self.start_service('compute')
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def test_service_reset_resets_cell_cache(self):
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"""Tests that the cell cache for database transaction context managers
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is cleared after a service reset (example scenario: SIGHUP).
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"""
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server_req = self._build_minimal_create_server_request(
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self.api, 'test-service-reset')
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server = self.api.post_server({'server': server_req})
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self._wait_for_state_change(self.api, server, 'ACTIVE')
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# Cell cache should be populated after creating a server.
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self.assertTrue(nova_context.CELL_CACHE)
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self.scheduler.reset()
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# Cell cache should be empty after the service reset.
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self.assertEqual({}, nova_context.CELL_CACHE)
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# Now test the WSGI service.
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server = self.api.post_server({'server': server_req})
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self._wait_for_state_change(self.api, server, 'ACTIVE')
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# Cell cache should be populated after creating a server.
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self.assertTrue(nova_context.CELL_CACHE)
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self.metadata.reset()
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# Cell cache should be empty after the service reset.
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self.assertEqual({}, nova_context.CELL_CACHE)
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def test_service_start_resets_cell_cache(self):
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"""Tests that the cell cache for database transaction context managers
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is cleared upon a service start (example scenario: service start after
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a SIGTERM and the parent process forks child process workers).
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"""
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server_req = self._build_minimal_create_server_request(
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self.api, 'test-service-start')
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server = self.api.post_server({'server': server_req})
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self._wait_for_state_change(self.api, server, 'ACTIVE')
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# Cell cache should be populated after creating a server.
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self.assertTrue(nova_context.CELL_CACHE)
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self.scheduler.stop()
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# NOTE(melwitt): Simulate a service starting after being stopped. The
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# scenario we want to handle is one where during start, the parent
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# process forks child process workers while one or more of its cached
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# database transaction context managers is inside a locked code
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# section. If the child processes are forked while the lock is locked,
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# the child processes begin with an already locked lock that can never
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# be acquired again. The result is that requests gets stuck and fail
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# with a CellTimeout error.
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self.scheduler.start()
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# Cell cache should be empty after the service start.
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self.assertEqual({}, nova_context.CELL_CACHE)
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# Now test the WSGI service.
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server = self.api.post_server({'server': server_req})
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self._wait_for_state_change(self.api, server, 'ACTIVE')
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# Cell cache should be populated after creating a server.
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self.assertTrue(nova_context.CELL_CACHE)
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self.metadata.stop()
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self.metadata.start()
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# Cell cache should be empty after the service reset.
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self.assertEqual({}, nova_context.CELL_CACHE)
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