From 1429760d657edf28145d8cda63bb867df3c60bde Mon Sep 17 00:00:00 2001
From: Chris Dent <cdent@anticdent.org>
Date: Tue, 30 Aug 2016 10:22:36 +0000
Subject: [PATCH] Optional separate database for placement API

If 'connection' is set in the 'placement_database' conf group use
that as the connection URL for the placement database. Otherwise if
it is None, the default, then use the entire api_database conf group
to configure a database connection.

When placement_database.connection is not None a replica of the
structure of the API database is used, using the same migrations
used for the API database.

A placement_context_manager is added and used by the OVO objects in
nova.api.openstack.placement.objects.*. If there is no separate
placement database, this is still used, but points to the API
database.

nova.test and nova.test.fixtures are adjusted to add awareness of
the placement database.

This functionality is being provided to allow deployers to choose
between establishing a new database now or requiring a migration
later. The default is migration later. A reno is added to explain
the existence of the configuration setting.

This change returns the behavior removed by the revert in commit
39fb302fd9c8fc57d3e4bea1c60a02ad5067163f but done in a more
appropriate way.

Note that with the advent of the nova-status command, which checks
to see if placement is "ready" the tests here had to be adjusted.
If we do allow a separate database the code will now check the
separate database (if configured), but nothing is done with regard
to migrating from the api to placement database or checking that.

blueprint placement-extract

Change-Id: I7e1e89cd66397883453935dcf7172d977bf82e84
Implements: blueprint optional-placement-database
Co-Authored-By: Roman Podoliaka <rpodolyaka@mirantis.com>
---
 .../openstack/placement/objects/consumer.py   |   6 +-
 .../openstack/placement/objects/project.py    |   6 +-
 .../placement/objects/resource_provider.py    | 106 +++++++++---------
 nova/api/openstack/placement/objects/user.py  |   6 +-
 nova/conf/database.py                         |  55 ++++++++-
 nova/db/sqlalchemy/api.py                     |  11 ++
 nova/db/sqlalchemy/migration.py               |   8 +-
 nova/test.py                                  |   1 +
 nova/tests/fixtures.py                        |  10 +-
 .../db/test_allocation_candidates.py          |   2 +-
 .../api/openstack/placement/db/test_base.py   |   3 +-
 .../openstack/placement/db/test_consumer.py   |   8 +-
 .../placement/db/test_resource_class_cache.py |   2 +-
 .../placement/db/test_resource_provider.py    |   8 +-
 .../openstack/placement/fixtures/gabbits.py   |   9 +-
 .../api/openstack/placement/test_direct.py    |   2 +-
 .../placement-database-2e087f379273535d.yaml  |  23 ++++
 17 files changed, 185 insertions(+), 81 deletions(-)
 create mode 100644 releasenotes/notes/placement-database-2e087f379273535d.yaml

diff --git a/nova/api/openstack/placement/objects/consumer.py b/nova/api/openstack/placement/objects/consumer.py
index 2e2697f8a..e4669a6cf 100644
--- a/nova/api/openstack/placement/objects/consumer.py
+++ b/nova/api/openstack/placement/objects/consumer.py
@@ -25,7 +25,7 @@ CONSUMER_TBL = models.Consumer.__table__
 _ALLOC_TBL = models.Allocation.__table__
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def create_incomplete_consumers(ctx, batch_size):
     """Finds all the consumer records that are missing for allocations and
     creates consumer records for them, using the "incomplete consumer" project
@@ -62,7 +62,7 @@ def create_incomplete_consumers(ctx, batch_size):
     return res.rowcount, res.rowcount
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_consumer_by_uuid(ctx, uuid):
     # The SQL for this looks like the following:
     # SELECT
@@ -136,7 +136,7 @@ class Consumer(base.VersionedObject, base.TimestampedObject):
         return cls._from_db_object(ctx, cls(ctx), res)
 
     def create(self):
-        @db_api.api_context_manager.writer
+        @db_api.placement_context_manager.writer
         def _create_in_db(ctx):
             db_obj = models.Consumer(
                 uuid=self.uuid, project_id=self.project.id,
diff --git a/nova/api/openstack/placement/objects/project.py b/nova/api/openstack/placement/objects/project.py
index eac3c7ff3..d26f2c486 100644
--- a/nova/api/openstack/placement/objects/project.py
+++ b/nova/api/openstack/placement/objects/project.py
@@ -24,7 +24,7 @@ CONF = cfg.CONF
 PROJECT_TBL = models.Project.__table__
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def ensure_incomplete_project(ctx):
     """Ensures that a project record is created for the "incomplete consumer
     project". Returns the internal ID of that record.
@@ -40,7 +40,7 @@ def ensure_incomplete_project(ctx):
     return res.inserted_primary_key[0]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_project_by_external_id(ctx, external_id):
     projects = sa.alias(PROJECT_TBL, name="p")
     cols = [
@@ -81,7 +81,7 @@ class Project(base.VersionedObject):
         return cls._from_db_object(ctx, cls(ctx), res)
 
     def create(self):
-        @db_api.api_context_manager.writer
+        @db_api.placement_context_manager.writer
         def _create_in_db(ctx):
             db_obj = models.Project(external_id=self.external_id)
             try:
diff --git a/nova/api/openstack/placement/objects/resource_provider.py b/nova/api/openstack/placement/objects/resource_provider.py
index dad0ca10b..67c0858a3 100644
--- a/nova/api/openstack/placement/objects/resource_provider.py
+++ b/nova/api/openstack/placement/objects/resource_provider.py
@@ -67,7 +67,7 @@ CONF = cfg.CONF
 LOG = logging.getLogger(__name__)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _ensure_rc_cache(ctx):
     """Ensures that a singleton resource class cache has been created in the
     module's scope.
@@ -84,7 +84,7 @@ def _ensure_rc_cache(ctx):
 @oslo_db_api.wrap_db_retry(max_retries=5, retry_on_deadlock=True)
 # Bug #1760322: If the caller raises an exception, we don't want the trait
 # sync rolled back; so use an .independent transaction
-@db_api.api_context_manager.writer.independent
+@db_api.placement_context_manager.writer.independent
 def _trait_sync(ctx):
     """Sync the os_traits symbols to the database.
 
@@ -282,7 +282,7 @@ def _increment_provider_generation(ctx, rp):
     return new_generation
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _add_inventory(context, rp, inventory):
     """Add one Inventory that wasn't already on the provider.
 
@@ -297,7 +297,7 @@ def _add_inventory(context, rp, inventory):
     rp.generation = _increment_provider_generation(context, rp)
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _update_inventory(context, rp, inventory):
     """Update an inventory already on the provider.
 
@@ -313,7 +313,7 @@ def _update_inventory(context, rp, inventory):
     return exceeded
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _delete_inventory(context, rp, resource_class):
     """Delete up to one Inventory of the given resource_class string.
 
@@ -329,7 +329,7 @@ def _delete_inventory(context, rp, resource_class):
     rp.generation = _increment_provider_generation(context, rp)
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _set_inventory(context, rp, inv_list):
     """Given an InventoryList object, replaces the inventory of the
     resource provider in a safe, atomic fashion using the resource
@@ -385,7 +385,7 @@ def _set_inventory(context, rp, inv_list):
     return exceeded
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_provider_by_uuid(context, uuid):
     """Given a UUID, return a dict of information about the resource provider
     from the database.
@@ -419,7 +419,7 @@ def _get_provider_by_uuid(context, uuid):
     return dict(res)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_aggregates_by_provider_id(context, rp_id):
     join_statement = sa.join(
         _AGG_TBL, _RP_AGG_TBL, sa.and_(
@@ -429,7 +429,7 @@ def _get_aggregates_by_provider_id(context, rp_id):
     return [r[0] for r in context.session.execute(sel).fetchall()]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _anchors_for_sharing_providers(context, rp_ids, get_id=False):
     """Given a list of internal IDs of sharing providers, returns a set of
     tuples of (sharing provider UUID, anchor provider UUID), where each of
@@ -485,7 +485,7 @@ def _anchors_for_sharing_providers(context, rp_ids, get_id=False):
     return set([(r[0], r[1]) for r in context.session.execute(sel).fetchall()])
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _set_aggregates(context, resource_provider, provided_aggregates,
                     increment_generation=False):
     rp_id = resource_provider.id
@@ -550,7 +550,7 @@ def _set_aggregates(context, resource_provider, provided_aggregates,
             context, resource_provider)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_traits_by_provider_id(context, rp_id):
     t = sa.alias(_TRAIT_TBL, name='t')
     rpt = sa.alias(_RP_TRAIT_TBL, name='rpt')
@@ -602,7 +602,7 @@ def _delete_traits_from_provider(ctx, rp_id, to_delete):
     ctx.session.execute(del_stmt)
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _set_traits(context, rp, traits):
     """Given a ResourceProvider object and a TraitList object, replaces the set
     of traits associated with the resource provider.
@@ -632,7 +632,7 @@ def _set_traits(context, rp, traits):
     rp.generation = _increment_provider_generation(context, rp)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _has_child_providers(context, rp_id):
     """Returns True if the supplied resource provider has any child providers,
     False otherwise
@@ -645,7 +645,7 @@ def _has_child_providers(context, rp_id):
     return False
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _set_root_provider_id(context, rp_id, root_id):
     """Simply sets the root_provider_id value for a provider identified by
     rp_id. Used in online data migration.
@@ -783,7 +783,7 @@ def _provider_ids_matching_aggregates(context, member_of):
     return [r[0] for r in context.session.execute(sel).fetchall()]
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _delete_rp_record(context, _id):
     return context.session.query(models.ResourceProvider).\
         filter(models.ResourceProvider.id == _id).\
@@ -917,7 +917,7 @@ class ResourceProvider(base.VersionedObject, base.TimestampedObject):
         _set_traits(self._context, self, traits)
         self.obj_reset_changes()
 
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _create_in_db(self, context, updates):
         parent_id = None
         root_id = None
@@ -962,7 +962,7 @@ class ResourceProvider(base.VersionedObject, base.TimestampedObject):
             self.root_provider_uuid = self.uuid
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _delete(context, _id):
         # Do a quick check to see if the provider is a parent. If it is, don't
         # allow deleting the provider. Note that the foreign key constraint on
@@ -1007,7 +1007,7 @@ class ResourceProvider(base.VersionedObject, base.TimestampedObject):
         if not result:
             raise exception.NotFound()
 
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _update_in_db(self, context, id, updates):
         if 'parent_provider_uuid' in updates:
             # TODO(jaypipes): For now, "re-parenting" and "un-parenting" are
@@ -1060,7 +1060,7 @@ class ResourceProvider(base.VersionedObject, base.TimestampedObject):
                     reason=_('parent provider UUID does not exist.'))
 
     @staticmethod
-    @db_api.api_context_manager.writer  # Needed for online data migration
+    @db_api.placement_context_manager.writer  # For online data migration
     def _from_db_object(context, resource_provider, db_resource_provider):
         # Online data migration to populate root_provider_id
         # TODO(jaypipes): Remove when all root_provider_id values are NOT NULL
@@ -1076,7 +1076,7 @@ class ResourceProvider(base.VersionedObject, base.TimestampedObject):
         return resource_provider
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_providers_with_shared_capacity(ctx, rc_id, amount, member_of=None):
     """Returns a list of resource provider IDs (internal IDs, not UUIDs)
     that have capacity for a requested amount of a resource and indicate that
@@ -1220,7 +1220,7 @@ class ResourceProviderList(base.ObjectListBase, base.VersionedObject):
     }
 
     @staticmethod
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _get_all_by_filters_from_db(context, filters):
         # Eg. filters can be:
         #  filters = {
@@ -1469,7 +1469,7 @@ class Inventory(base.VersionedObject, base.TimestampedObject):
         return int((self.total - self.reserved) * self.allocation_ratio)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_inventory_by_provider_id(ctx, rp_id):
     inv = sa.alias(_INV_TBL, name="i")
     cols = [
@@ -1545,7 +1545,7 @@ class Allocation(base.VersionedObject, base.TimestampedObject):
     }
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def _delete_allocations_for_consumer(ctx, consumer_id):
     """Deletes any existing allocations that correspond to the allocations to
     be written. This is wrapped in a transaction, so if the write subsequently
@@ -1715,7 +1715,7 @@ def _check_capacity_exceeded(ctx, allocs):
     return res_providers
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_allocations_by_provider_id(ctx, rp_id):
     allocs = sa.alias(_ALLOC_TBL, name="a")
     consumers = sa.alias(_CONSUMER_TBL, name="c")
@@ -1748,7 +1748,7 @@ def _get_allocations_by_provider_id(ctx, rp_id):
     return [dict(r) for r in ctx.session.execute(sel)]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_allocations_by_consumer_uuid(ctx, consumer_uuid):
     allocs = sa.alias(_ALLOC_TBL, name="a")
     rp = sa.alias(_RP_TBL, name="rp")
@@ -1786,7 +1786,7 @@ def _get_allocations_by_consumer_uuid(ctx, consumer_uuid):
     return [dict(r) for r in ctx.session.execute(sel)]
 
 
-@db_api.api_context_manager.writer.independent
+@db_api.placement_context_manager.writer.independent
 def _create_incomplete_consumers_for_provider(ctx, rp_id):
     # TODO(jaypipes): Remove in Stein after a blocker migration is added.
     """Creates consumer record if consumer relationship between allocations ->
@@ -1831,7 +1831,7 @@ def _create_incomplete_consumers_for_provider(ctx, rp_id):
                      res.rowcount)
 
 
-@db_api.api_context_manager.writer.independent
+@db_api.placement_context_manager.writer.independent
 def _create_incomplete_consumer(ctx, consumer_id):
     # TODO(jaypipes): Remove in Stein after a blocker migration is added.
     """Creates consumer record if consumer relationship between allocations ->
@@ -1870,7 +1870,7 @@ class AllocationList(base.ObjectListBase, base.VersionedObject):
     }
 
     @oslo_db_api.wrap_db_retry(max_retries=5, retry_on_deadlock=True)
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _set_allocations(self, context, allocs):
         """Write a set of allocations.
 
@@ -2082,7 +2082,7 @@ class UsageList(base.ObjectListBase, base.VersionedObject):
     }
 
     @staticmethod
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _get_all_by_resource_provider_uuid(context, rp_uuid):
         query = (context.session.query(models.Inventory.resource_class_id,
                  func.coalesce(func.sum(models.Allocation.used), 0))
@@ -2101,7 +2101,7 @@ class UsageList(base.ObjectListBase, base.VersionedObject):
         return result
 
     @staticmethod
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _get_all_by_project_user(context, project_id, user_id=None):
         query = (context.session.query(models.Allocation.resource_class_id,
                  func.coalesce(func.sum(models.Allocation.used), 0))
@@ -2181,7 +2181,7 @@ class ResourceClass(base.VersionedObject, base.TimestampedObject):
         return obj
 
     @staticmethod
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _get_next_id(context):
         """Utility method to grab the next resource class identifier to use for
          user-defined resource classes.
@@ -2240,7 +2240,7 @@ class ResourceClass(base.VersionedObject, base.TimestampedObject):
             raise exception.MaxDBRetriesExceeded(action=msg)
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _create_in_db(context, updates):
         next_id = ResourceClass._get_next_id(context)
         rc = models.ResourceClass()
@@ -2264,7 +2264,7 @@ class ResourceClass(base.VersionedObject, base.TimestampedObject):
         _RC_CACHE.clear()
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _destroy(context, _id, name):
         # Don't delete the resource class if it is referred to in the
         # inventories table.
@@ -2293,7 +2293,7 @@ class ResourceClass(base.VersionedObject, base.TimestampedObject):
         _RC_CACHE.clear()
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _save(context, id, name, updates):
         db_rc = context.session.query(models.ResourceClass).filter_by(
             id=id).first()
@@ -2312,7 +2312,7 @@ class ResourceClassList(base.ObjectListBase, base.VersionedObject):
     }
 
     @staticmethod
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _get_all(context):
         _ensure_rc_cache(context)
         customs = list(context.session.query(models.ResourceClass).all())
@@ -2349,7 +2349,7 @@ class Trait(base.VersionedObject, base.TimestampedObject):
         return trait
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _create_in_db(context, updates):
         trait = models.Trait()
         trait.update(updates)
@@ -2374,7 +2374,7 @@ class Trait(base.VersionedObject, base.TimestampedObject):
         self._from_db_object(self._context, self, db_trait)
 
     @staticmethod
-    @db_api.api_context_manager.writer  # trait sync can cause a write
+    @db_api.placement_context_manager.writer  # trait sync can cause a write
     def _get_by_name_from_db(context, name):
         _ensure_trait_sync(context)
         result = context.session.query(models.Trait).filter_by(
@@ -2389,7 +2389,7 @@ class Trait(base.VersionedObject, base.TimestampedObject):
         return cls._from_db_object(context, cls(), db_trait)
 
     @staticmethod
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _destroy_in_db(context, _id, name):
         num = context.session.query(models.ResourceProviderTrait).filter(
             models.ResourceProviderTrait.trait_id == _id).count()
@@ -2424,7 +2424,7 @@ class TraitList(base.ObjectListBase, base.VersionedObject):
     }
 
     @staticmethod
-    @db_api.api_context_manager.writer  # trait sync can cause a write
+    @db_api.placement_context_manager.writer  # trait sync can cause a write
     def _get_all_from_db(context, filters):
         _ensure_trait_sync(context)
         if not filters:
@@ -2535,7 +2535,7 @@ class ProviderSummary(base.VersionedObject):
         return set(res.resource_class for res in self.resources)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_usages_by_provider(ctx, rp_ids):
     """Returns a row iterator of usage records grouped by resource provider ID
     and resource class ID for all resource providers
@@ -2606,7 +2606,7 @@ def _get_usages_by_provider(ctx, rp_ids):
     return ctx.session.execute(query).fetchall()
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_provider_ids_having_any_trait(ctx, traits):
     """Returns a list of resource provider internal IDs that have ANY of the
     supplied traits.
@@ -2627,7 +2627,7 @@ def _get_provider_ids_having_any_trait(ctx, traits):
     return [r[0] for r in ctx.session.execute(sel)]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_provider_ids_having_all_traits(ctx, required_traits):
     """Returns a list of resource provider internal IDs that have ALL of the
     required traits.
@@ -2656,7 +2656,7 @@ def _get_provider_ids_having_all_traits(ctx, required_traits):
     return [r[0] for r in ctx.session.execute(sel)]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _has_provider_trees(ctx):
     """Simple method that returns whether provider trees (i.e. nested resource
     providers) are in use in the deployment at all. This information is used to
@@ -2673,7 +2673,7 @@ def _has_provider_trees(ctx):
     return len(res) > 0
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_provider_ids_matching(ctx, resources, required_traits,
         forbidden_traits, member_of=None):
     """Returns a list of tuples of (internal provider ID, root provider ID)
@@ -2805,7 +2805,7 @@ def _get_provider_ids_matching(ctx, resources, required_traits,
     return [(r[0], r[1]) for r in ctx.session.execute(sel)]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _provider_aggregates(ctx, rp_ids):
     """Given a list of resource provider internal IDs, returns a dict,
     keyed by those provider IDs, of sets of aggregate ids associated
@@ -2830,7 +2830,7 @@ def _provider_aggregates(ctx, rp_ids):
     return res
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_providers_with_resource(ctx, rc_id, amount):
     """Returns a set of tuples of (provider ID, root provider ID) of providers
     that satisfy the request for a single resource class.
@@ -2889,7 +2889,7 @@ def _get_providers_with_resource(ctx, rc_id, amount):
     return res
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_trees_with_traits(ctx, rp_ids, required_traits, forbidden_traits):
     """Given a list of provider IDs, filter them to return a set of tuples of
     (provider ID, root provider ID) of providers which belong to a tree that
@@ -2978,7 +2978,7 @@ def _get_trees_with_traits(ctx, rp_ids, required_traits, forbidden_traits):
     return [(rp_id, root_id) for rp_id, root_id in res]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_trees_matching_all(ctx, resources, required_traits, forbidden_traits,
                             sharing, member_of):
     """Returns a list of two-tuples (provider internal ID, root provider
@@ -3458,7 +3458,7 @@ def _alloc_candidates_multiple_providers(ctx, requested_resources,
     return alloc_requests, list(summaries.values())
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _provider_traits(ctx, rp_ids):
     """Given a list of resource provider internal IDs, returns a dict, keyed by
     those provider IDs, of string trait names associated with that provider.
@@ -3483,7 +3483,7 @@ def _provider_traits(ctx, rp_ids):
     return res
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _trait_ids_from_names(ctx, names):
     """Given a list of string trait names, returns a dict, keyed by those
     string names, of the corresponding internal integer trait ID.
@@ -3813,8 +3813,8 @@ class AllocationCandidates(base.VersionedObject):
     def _get_by_one_request(context, request):
         """Get allocation candidates for one RequestGroup.
 
-        Must be called from within an api_context_manager.reader (or writer)
-        context.
+        Must be called from within an placement_context_manager.reader
+        (or writer) context.
 
         :param context: Nova RequestContext.
         :param request: One nova.api.openstack.placement.util.RequestGroup
@@ -3895,7 +3895,7 @@ class AllocationCandidates(base.VersionedObject):
     # resource_providers table via ResourceProvider.get_by_uuid, which does
     # data migration to populate the root_provider_uuid.  Change this back to a
     # reader when that migration is no longer happening.
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _get_by_requests(cls, context, requests, limit=None,
                          group_policy=None):
         candidates = {}
diff --git a/nova/api/openstack/placement/objects/user.py b/nova/api/openstack/placement/objects/user.py
index 4a12ee2a3..412559636 100644
--- a/nova/api/openstack/placement/objects/user.py
+++ b/nova/api/openstack/placement/objects/user.py
@@ -24,7 +24,7 @@ CONF = cfg.CONF
 USER_TBL = models.User.__table__
 
 
-@db_api.api_context_manager.writer
+@db_api.placement_context_manager.writer
 def ensure_incomplete_user(ctx):
     """Ensures that a user record is created for the "incomplete consumer
     user". Returns the internal ID of that record.
@@ -40,7 +40,7 @@ def ensure_incomplete_user(ctx):
     return res.inserted_primary_key[0]
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_user_by_external_id(ctx, external_id):
     users = sa.alias(USER_TBL, name="u")
     cols = [
@@ -81,7 +81,7 @@ class User(base.VersionedObject):
         return cls._from_db_object(ctx, cls(ctx), res)
 
     def create(self):
-        @db_api.api_context_manager.writer
+        @db_api.placement_context_manager.writer
         def _create_in_db(ctx):
             db_obj = models.User(external_id=self.external_id)
             try:
diff --git a/nova/conf/database.py b/nova/conf/database.py
index 78d881b8a..0b6164946 100644
--- a/nova/conf/database.py
+++ b/nova/conf/database.py
@@ -104,10 +104,61 @@ def enrich_help_text(alt_db_opts):
                 # texts here if needed.
                 alt_db_opt.help = db_opt.help + alt_db_opt.help
 
+# NOTE(cdent): See the note above on api_db_group. The same issues
+# apply here.
+
+placement_db_group = cfg.OptGroup('placement_database',
+                                  title='Placement API database options',
+                                  help="""
+The *Placement API Database* is a separate database which can be used with the
+placement service. This database is optional: if the connection option is not
+set, the nova api database will be used instead.
+""")
+
+placement_db_opts = [
+    cfg.StrOpt('connection',
+        help='',
+        secret=True),
+    cfg.StrOpt('connection_parameters',
+        default='',
+        help=''),
+    cfg.BoolOpt('sqlite_synchronous',
+        default=True,
+        help=''),
+    cfg.StrOpt('slave_connection',
+        secret=True,
+        help=''),
+    cfg.StrOpt('mysql_sql_mode',
+        default='TRADITIONAL',
+        help=''),
+    cfg.IntOpt('connection_recycle_time',
+        default=3600,
+        help=''),
+    cfg.IntOpt('max_pool_size',
+        help=''),
+    cfg.IntOpt('max_retries',
+        default=10,
+        help=''),
+    cfg.IntOpt('retry_interval',
+        default=10,
+        help=''),
+    cfg.IntOpt('max_overflow',
+        help=''),
+    cfg.IntOpt('connection_debug',
+        default=0,
+        help=''),
+    cfg.BoolOpt('connection_trace',
+        default=False,
+        help=''),
+    cfg.IntOpt('pool_timeout',
+        help=''),
+]  # noqa
+
 
 def register_opts(conf):
     oslo_db_options.set_defaults(conf, connection=_DEFAULT_SQL_CONNECTION)
     conf.register_opts(api_db_opts, group=api_db_group)
+    conf.register_opts(placement_db_opts, group=placement_db_group)
 
 
 def list_opts():
@@ -119,6 +170,8 @@ def list_opts():
     # in the "sample.conf" file, I omit the listing of the "oslo_db_options"
     # here.
     enrich_help_text(api_db_opts)
+    enrich_help_text(placement_db_opts)
     return {
-        api_db_group: api_db_opts
+        api_db_group: api_db_opts,
+        placement_db_group: placement_db_opts,
     }
diff --git a/nova/db/sqlalchemy/api.py b/nova/db/sqlalchemy/api.py
index f7e01ec2c..8afd05304 100644
--- a/nova/db/sqlalchemy/api.py
+++ b/nova/db/sqlalchemy/api.py
@@ -79,6 +79,7 @@ LOG = logging.getLogger(__name__)
 
 main_context_manager = enginefacade.transaction_context()
 api_context_manager = enginefacade.transaction_context()
+placement_context_manager = enginefacade.transaction_context()
 
 
 def _get_db_conf(conf_group, connection=None):
@@ -99,6 +100,12 @@ def _context_manager_from_context(context):
 def configure(conf):
     main_context_manager.configure(**_get_db_conf(conf.database))
     api_context_manager.configure(**_get_db_conf(conf.api_database))
+    if conf.placement_database.connection is None:
+        placement_context_manager.configure(
+            **_get_db_conf(conf.api_database))
+    else:
+        placement_context_manager.configure(
+            **_get_db_conf(conf.placement_database))
 
     if profiler_sqlalchemy and CONF.profiler.enabled \
             and CONF.profiler.trace_sqlalchemy:
@@ -141,6 +148,10 @@ def get_api_engine():
     return api_context_manager.get_legacy_facade().get_engine()
 
 
+def get_placement_engine():
+    return placement_context_manager.get_legacy_facade().get_engine()
+
+
 _SHADOW_TABLE_PREFIX = 'shadow_'
 _DEFAULT_QUOTA_NAME = 'default'
 PER_PROJECT_QUOTAS = ['fixed_ips', 'floating_ips', 'networks']
diff --git a/nova/db/sqlalchemy/migration.py b/nova/db/sqlalchemy/migration.py
index a8a544999..a61748b1d 100644
--- a/nova/db/sqlalchemy/migration.py
+++ b/nova/db/sqlalchemy/migration.py
@@ -31,6 +31,7 @@ from nova.i18n import _
 INIT_VERSION = {}
 INIT_VERSION['main'] = 215
 INIT_VERSION['api'] = 0
+INIT_VERSION['placement'] = 0
 _REPOSITORY = {}
 
 LOG = logging.getLogger(__name__)
@@ -41,6 +42,8 @@ def get_engine(database='main', context=None):
         return db_session.get_engine(context=context)
     if database == 'api':
         return db_session.get_api_engine()
+    if database == 'placement':
+        return db_session.get_placement_engine()
 
 
 def db_sync(version=None, database='main', context=None):
@@ -169,7 +172,10 @@ def _find_migrate_repo(database='main'):
     """Get the path for the migrate repository."""
     global _REPOSITORY
     rel_path = 'migrate_repo'
-    if database == 'api':
+    if database == 'api' or database == 'placement':
+        # NOTE(cdent): For the time being the placement database (if
+        # it is being used) is a replica (in structure) of the api
+        # database.
         rel_path = os.path.join('api_migrations', 'migrate_repo')
     path = os.path.join(os.path.abspath(os.path.dirname(__file__)),
                         rel_path)
diff --git a/nova/test.py b/nova/test.py
index 7a6283247..1c93a3ae1 100644
--- a/nova/test.py
+++ b/nova/test.py
@@ -290,6 +290,7 @@ class TestCase(testtools.TestCase):
             # NOTE(danms): Full database setup involves a cell0, cell1,
             # and the relevant mappings.
             self.useFixture(nova_fixtures.Database(database='api'))
+            self.useFixture(nova_fixtures.Database(database='placement'))
             self._setup_cells()
             self.useFixture(nova_fixtures.DefaultFlavorsFixture())
         elif not self.USES_DB_SELF:
diff --git a/nova/tests/fixtures.py b/nova/tests/fixtures.py
index 23d2f026c..28f757adb 100644
--- a/nova/tests/fixtures.py
+++ b/nova/tests/fixtures.py
@@ -58,7 +58,7 @@ from nova.tests import uuidsentinel
 _TRUE_VALUES = ('True', 'true', '1', 'yes')
 
 CONF = cfg.CONF
-DB_SCHEMA = {'main': "", 'api': ""}
+DB_SCHEMA = {'main': "", 'api': "", 'placement': ""}
 SESSION_CONFIGURED = False
 
 
@@ -571,7 +571,7 @@ class Database(fixtures.Fixture):
     def __init__(self, database='main', connection=None):
         """Create a database fixture.
 
-        :param database: The type of database, 'main' or 'api'
+        :param database: The type of database, 'main', 'api' or 'placement'
         :param connection: The connection string to use
         """
         super(Database, self).__init__()
@@ -592,6 +592,8 @@ class Database(fixtures.Fixture):
                 self.get_engine = session.get_engine
         elif database == 'api':
             self.get_engine = session.get_api_engine
+        elif database == 'placement':
+            self.get_engine = session.get_placement_engine
 
     def _cache_schema(self):
         global DB_SCHEMA
@@ -625,7 +627,7 @@ class DatabaseAtVersion(fixtures.Fixture):
         """Create a database fixture.
 
         :param version: Max version to sync to (or None for current)
-        :param database: The type of database, 'main' or 'api'
+        :param database: The type of database, 'main', 'api', 'placement'
         """
         super(DatabaseAtVersion, self).__init__()
         self.database = database
@@ -634,6 +636,8 @@ class DatabaseAtVersion(fixtures.Fixture):
             self.get_engine = session.get_engine
         elif database == 'api':
             self.get_engine = session.get_api_engine
+        elif database == 'placement':
+            self.get_engine = session.get_placement_engine
 
     def cleanup(self):
         engine = self.get_engine()
diff --git a/nova/tests/functional/api/openstack/placement/db/test_allocation_candidates.py b/nova/tests/functional/api/openstack/placement/db/test_allocation_candidates.py
index f91b6abf2..f1711b57d 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_allocation_candidates.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_allocation_candidates.py
@@ -1954,7 +1954,7 @@ class AllocationCandidatesTestCase(tb.PlacementDbBaseTestCase):
         names = map(six.text_type, names)
         sel = sa.select([rp_obj._RP_TBL.c.id])
         sel = sel.where(rp_obj._RP_TBL.c.name.in_(names))
-        with self.api_db.get_engine().connect() as conn:
+        with self.placement_db.get_engine().connect() as conn:
             rp_ids = set([r[0] for r in conn.execute(sel)])
         return rp_ids
 
diff --git a/nova/tests/functional/api/openstack/placement/db/test_base.py b/nova/tests/functional/api/openstack/placement/db/test_base.py
index da2361860..bcf62b8c3 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_base.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_base.py
@@ -53,7 +53,8 @@ class PlacementDbBaseTestCase(test.NoDBTestCase):
     def setUp(self):
         super(PlacementDbBaseTestCase, self).setUp()
         self.useFixture(fixtures.Database())
-        self.api_db = self.useFixture(fixtures.Database(database='api'))
+        self.placement_db = self.useFixture(
+                fixtures.Database(database='placement'))
         # Reset the _TRAITS_SYNCED global before we start and after
         # we are done since other tests (notably the gabbi tests)
         # may have caused it to change.
diff --git a/nova/tests/functional/api/openstack/placement/db/test_consumer.py b/nova/tests/functional/api/openstack/placement/db/test_consumer.py
index e0587d84c..67120270c 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_consumer.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_consumer.py
@@ -55,7 +55,7 @@ class ConsumerTestCase(tb.PlacementDbBaseTestCase):
         self.assertRaises(exception.ConsumerExists, c.create)
 
 
-@db_api.api_context_manager.reader
+@db_api.placement_context_manager.reader
 def _get_allocs_with_no_consumer_relationship(ctx):
     alloc_to_consumer = sa.outerjoin(
         ALLOC_TBL, CONSUMER_TBL,
@@ -75,10 +75,10 @@ class CreateIncompleteConsumersTestCase(test.NoDBTestCase):
     def setUp(self):
         super(CreateIncompleteConsumersTestCase, self).setUp()
         self.useFixture(fixtures.Database())
-        self.api_db = self.useFixture(fixtures.Database(database='api'))
+        self.api_db = self.useFixture(fixtures.Database(database='placement'))
         self.ctx = context.RequestContext('fake-user', 'fake-project')
 
-    @db_api.api_context_manager.writer
+    @db_api.placement_context_manager.writer
     def _create_incomplete_allocations(self, ctx):
         # Create some allocations with consumers that don't exist in the
         # consumers table to represent old allocations that we expect to be
@@ -105,7 +105,7 @@ class CreateIncompleteConsumersTestCase(test.NoDBTestCase):
         res = ctx.session.execute(sel).fetchall()
         self.assertEqual(0, len(res))
 
-    @db_api.api_context_manager.reader
+    @db_api.placement_context_manager.reader
     def _check_incomplete_consumers(self, ctx):
         incomplete_external_id = CONF.placement.incomplete_consumer_project_id
 
diff --git a/nova/tests/functional/api/openstack/placement/db/test_resource_class_cache.py b/nova/tests/functional/api/openstack/placement/db/test_resource_class_cache.py
index 8ab48a1db..414f6cdef 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_resource_class_cache.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_resource_class_cache.py
@@ -26,7 +26,7 @@ class TestResourceClassCache(test.TestCase):
 
     def setUp(self):
         super(TestResourceClassCache, self).setUp()
-        self.db = self.useFixture(fixtures.Database(database='api'))
+        self.db = self.useFixture(fixtures.Database(database='placement'))
         self.context = mock.Mock()
         sess_mock = mock.Mock()
         sess_mock.connection.side_effect = self.db.get_engine().connect
diff --git a/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py b/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
index e77d619b6..ca768b033 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
@@ -120,7 +120,7 @@ class ResourceProviderTestCase(tb.PlacementDbBaseTestCase):
         the provider's UUID.
         """
         rp_tbl = rp_obj._RP_TBL
-        conn = self.api_db.get_engine().connect()
+        conn = self.placement_db.get_engine().connect()
 
         # First, set up a record for an "old-style" resource provider with no
         # root provider UUID.
@@ -396,7 +396,7 @@ class ResourceProviderTestCase(tb.PlacementDbBaseTestCase):
         self.assertEqual([], rps.objects)
 
         rp_tbl = rp_obj._RP_TBL
-        conn = self.api_db.get_engine().connect()
+        conn = self.placement_db.get_engine().connect()
 
         # First, set up a record for an "old-style" resource provider with no
         # root provider UUID.
@@ -1736,7 +1736,7 @@ class ResourceClassListTestCase(tb.PlacementDbBaseTestCase):
             ('CUSTOM_IRON_NFV', 10001),
             ('CUSTOM_IRON_ENTERPRISE', 10002),
         ]
-        with self.api_db.get_engine().connect() as conn:
+        with self.placement_db.get_engine().connect() as conn:
             for custom in customs:
                 c_name, c_id = custom
                 ins = rp_obj._RC_TBL.insert().values(id=c_id, name=c_name)
@@ -2198,7 +2198,7 @@ class ResourceProviderTraitTestCase(tb.PlacementDbBaseTestCase):
         list all traits, os_traits have been synchronized.
         """
         std_traits = os_traits.get_traits()
-        conn = self.api_db.get_engine().connect()
+        conn = self.placement_db.get_engine().connect()
 
         def _db_traits(conn):
             sel = sa.select([rp_obj._TRAIT_TBL.c.name])
diff --git a/nova/tests/functional/api/openstack/placement/fixtures/gabbits.py b/nova/tests/functional/api/openstack/placement/fixtures/gabbits.py
index 63e574000..5d3a4194d 100644
--- a/nova/tests/functional/api/openstack/placement/fixtures/gabbits.py
+++ b/nova/tests/functional/api/openstack/placement/fixtures/gabbits.py
@@ -61,6 +61,8 @@ class APIFixture(fixture.GabbiFixture):
         self.conf.set_override('connection', "sqlite://", group='database')
         self.conf.set_override('connection', "sqlite://",
                                group='api_database')
+        self.conf.set_override('connection', "sqlite://",
+                               group='placement_database')
 
         # Register CORS opts, but do not set config. This has the
         # effect of exercising the "don't use cors" path in
@@ -73,12 +75,14 @@ class APIFixture(fixture.GabbiFixture):
         config.parse_args([], default_config_files=[], configure_db=False,
                           init_rpc=False)
 
-        # NOTE(cdent): The main database is not used but we still need to
-        # manage it to make the fixtures work correctly and not cause
+        # NOTE(cdent): All three database fixtures need to be
+        # managed for database handling to work and not cause
         # conflicts with other tests in the same process.
         self._reset_db_flags()
+        self.placement_db_fixture = fixtures.Database('placement')
         self.api_db_fixture = fixtures.Database('api')
         self.main_db_fixture = fixtures.Database('main')
+        self.placement_db_fixture.reset()
         self.api_db_fixture.reset()
         self.main_db_fixture.reset()
 
@@ -96,6 +100,7 @@ class APIFixture(fixture.GabbiFixture):
         os.environ['ALT_PARENT_PROVIDER_UUID'] = uuidutils.generate_uuid()
 
     def stop_fixture(self):
+        self.placement_db_fixture.cleanup()
         self.api_db_fixture.cleanup()
         self.main_db_fixture.cleanup()
 
diff --git a/nova/tests/functional/api/openstack/placement/test_direct.py b/nova/tests/functional/api/openstack/placement/test_direct.py
index 1ef0e43fe..fb323a64d 100644
--- a/nova/tests/functional/api/openstack/placement/test_direct.py
+++ b/nova/tests/functional/api/openstack/placement/test_direct.py
@@ -29,7 +29,7 @@ class TestDirect(test.NoDBTestCase):
 
     def setUp(self):
         super(TestDirect, self).setUp()
-        self.api_db = self.useFixture(fixtures.Database(database='api'))
+        self.api_db = self.useFixture(fixtures.Database(database='placement'))
         self._reset_traits_synced()
         self.context = context.get_admin_context()
         self.addCleanup(self._reset_traits_synced)
diff --git a/releasenotes/notes/placement-database-2e087f379273535d.yaml b/releasenotes/notes/placement-database-2e087f379273535d.yaml
new file mode 100644
index 000000000..a3b081a93
--- /dev/null
+++ b/releasenotes/notes/placement-database-2e087f379273535d.yaml
@@ -0,0 +1,23 @@
+---
+features:
+  - |
+    An optional configuration group ``placement_database`` can be used in
+    nova.conf to configure a separate database for use with the placement
+    API.
+
+    If ``placement_database.connection`` has a value then the
+    ``placement_database`` configuration group will be used to configure a
+    separate placement database, including using ``connection`` to identify the
+    target database. That database will have a schema that is a replica of all
+    the tables used in the API database. The new database will be created and
+    synchronized when the ``nova-manage api_db sync`` command is run.
+
+    When the ``placement_database.connection`` setting is omitted the existing
+    settings for the ``api_database`` will be used for hosting placement data.
+
+    Setting ``placement_database.connection`` and calling
+    ``nova-manage api_db sync`` will only create tables. No data will be
+    migrated. In an existing OpenStack deployment, if there is existing
+    placement data in the ``nova_api`` database this will not be copied. It is
+    up to the deployment to manually replicate that data in a fashion that
+    works best for the environment.