diff --git a/synapse/storage/databases/__init__.py b/synapse/storage/databases/__init__.py
new file mode 100644
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+++ b/synapse/storage/databases/__init__.py
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+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+from synapse.storage.database import DatabasePool, make_conn
+from synapse.storage.databases.main.events import PersistEventsStore
+from synapse.storage.databases.state import StateGroupDataStore
+from synapse.storage.engines import create_engine
+from synapse.storage.prepare_database import prepare_database
+
+logger = logging.getLogger(__name__)
+
+
+class Databases(object):
+ """The various databases.
+
+ These are low level interfaces to physical databases.
+
+ Attributes:
+ main (DataStore)
+ """
+
+ def __init__(self, main_store_class, hs):
+ # Note we pass in the main store class here as workers use a different main
+ # store.
+
+ self.databases = []
+ main = None
+ state = None
+ persist_events = None
+
+ for database_config in hs.config.database.databases:
+ db_name = database_config.name
+ engine = create_engine(database_config.config)
+
+ with make_conn(database_config, engine) as db_conn:
+ logger.info("Preparing database %r...", db_name)
+
+ engine.check_database(db_conn)
+ prepare_database(
+ db_conn, engine, hs.config, databases=database_config.databases,
+ )
+
+ database = DatabasePool(hs, database_config, engine)
+
+ if "main" in database_config.databases:
+ logger.info("Starting 'main' data store")
+
+ # Sanity check we don't try and configure the main store on
+ # multiple databases.
+ if main:
+ raise Exception("'main' data store already configured")
+
+ main = main_store_class(database, db_conn, hs)
+
+ # If we're on a process that can persist events also
+ # instantiate a `PersistEventsStore`
+ if hs.config.worker.writers.events == hs.get_instance_name():
+ persist_events = PersistEventsStore(hs, database, main)
+
+ if "state" in database_config.databases:
+ logger.info("Starting 'state' data store")
+
+ # Sanity check we don't try and configure the state store on
+ # multiple databases.
+ if state:
+ raise Exception("'state' data store already configured")
+
+ state = StateGroupDataStore(database, db_conn, hs)
+
+ db_conn.commit()
+
+ self.databases.append(database)
+
+ logger.info("Database %r prepared", db_name)
+
+ # Sanity check that we have actually configured all the required stores.
+ if not main:
+ raise Exception("No 'main' data store configured")
+
+ if not state:
+ raise Exception("No 'main' data store configured")
+
+ # We use local variables here to ensure that the databases do not have
+ # optional types.
+ self.main = main
+ self.state = state
+ self.persist_events = persist_events
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