Cache database and message queue connection objects
Recently in the gate we have seen a trace on some work-in-progress
patches:
OperationalError: (pymysql.err.OperationalError)
(1040, u'Too many connections')
and at least one operator has reported that the number of database
connections increased significantly going from Mitaka to Newton.
It was suspected that the increase was caused by creating new oslo.db
transaction context managers on-the-fly when switching database
connections for cells. Comparing the dstat --tcp output of runs of the
gate-tempest-dsvm-neutron-full-ubuntu-xenial job with and without
caching of the database connections showed a difference of 445 active
TCP connections and 1495 active TCP connections, respectively [1].
This adds caching of the oslo.db transaction context managers and the
oslo.messaging transports to avoid creating a large number of objects
that are not being garbage-collected as expected.
Closes-Bug: #1691545
[1] https://docs.google.com/spreadsheets/d/1DIfFfX3kaA_SRoCM-aO7BN4IBEShChXLztOBFeKryt4/edit?usp=sharing
Conflicts:
nova/context.py
nova/tests/unit/test_context.py
NOTE(melwitt): Conflicts caused by the fact that the set_target_cell
function doesn't exist in Ocata and message queue connections were
not stored on the context in Ocata.
Change-Id: I17e0eb836dd87aac5859f506e7d771d42753d31a
(cherry picked from commit 47fa88d947
)
This commit is contained in:
parent
7ccf8d2e35
commit
f4159d1755
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@ -34,6 +34,10 @@ 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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class _ContextAuthPlugin(plugin.BaseAuthPlugin):
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@ -366,11 +370,27 @@ def target_cell(context, cell_mapping):
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:param context: The RequestContext to add connection information
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:param cell_mapping: A objects.CellMapping object
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"""
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global CELL_CACHE
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original_db_connection = context.db_connection
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# avoid circular import
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from nova import db
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db_connection_string = cell_mapping.database_connection
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context.db_connection = db.create_context_manager(db_connection_string)
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# Synchronize access to the cache by multiple API workers.
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@utils.synchronized(cell_mapping.uuid)
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def get_or_set_cached_cell_and_set_connections():
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try:
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cell_db_conn = CELL_CACHE[cell_mapping.uuid]
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except KeyError:
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db_connection_string = cell_mapping.database_connection
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context.db_connection = db.create_context_manager(
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db_connection_string)
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CELL_CACHE[cell_mapping.uuid] = context.db_connection
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else:
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context.db_connection = cell_db_conn
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get_or_set_cached_cell_and_set_connections()
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try:
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yield context
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finally:
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@ -233,6 +233,7 @@ class TestCase(testtools.TestCase):
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# NOTE(danms): Reset the cached list of cells
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from nova.compute import api
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api.CELLS = []
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context.CELL_CACHE = {}
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self.cell_mappings = {}
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self.host_mappings = {}
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@ -20,6 +20,7 @@ from nova import context
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from nova import exception
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from nova import objects
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from nova import test
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from nova.tests import uuidsentinel as uuids
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class ContextTestCase(test.NoDBTestCase):
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@ -298,7 +299,9 @@ class ContextTestCase(test.NoDBTestCase):
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roles=['admin', 'weasel'])
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# Verify the existing db_connection, if any, is restored
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ctxt.db_connection = mock.sentinel.db_conn
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mapping = objects.CellMapping(database_connection='fake://')
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mapping = objects.CellMapping(database_connection='fake://',
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transport_url='fake://',
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uuid=uuids.cell)
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with context.target_cell(ctxt, mapping):
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self.assertEqual(ctxt.db_connection, mock.sentinel.cm)
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self.assertEqual(mock.sentinel.db_conn, ctxt.db_connection)
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@ -308,3 +311,20 @@ class ContextTestCase(test.NoDBTestCase):
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self.assertIsNone(ctxt.user_id)
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self.assertIsNone(ctxt.project_id)
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self.assertFalse(ctxt.is_admin)
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@mock.patch('nova.db.create_context_manager')
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def test_target_cell_caching(self, mock_create_cm):
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mock_create_cm.return_value = mock.sentinel.db_conn_obj
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ctxt = context.get_context()
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mapping = objects.CellMapping(database_connection='fake://db',
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transport_url='fake://mq',
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uuid=uuids.cell)
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# First call should create new connection objects.
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with context.target_cell(ctxt, mapping):
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self.assertEqual(mock.sentinel.db_conn_obj, ctxt.db_connection)
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mock_create_cm.assert_called_once_with('fake://db')
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# Second call should use cached objects.
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mock_create_cm.reset_mock()
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with context.target_cell(ctxt, mapping):
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self.assertEqual(mock.sentinel.db_conn_obj, ctxt.db_connection)
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mock_create_cm.assert_not_called()
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@ -0,0 +1,10 @@
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---
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fixes:
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- |
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Fixes `bug 1691545`_ in which there was a significant increase in database
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connections because of the way connections to cell databases were being
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established. With this fix, objects related to database connections are
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cached in the API service and reused to prevent new connections being
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established for every communication with cell databases.
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.. _bug 1691545: https://bugs.launchpad.net/nova/+bug/1691545
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