diff --git a/changelog.d/6847.misc b/changelog.d/6847.misc
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+++ b/changelog.d/6847.misc
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+Populate `rooms.room_version` database column at startup, rather than in a background update.
diff --git a/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.postgres b/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.postgres
new file mode 100644
index 000000000..c601cff6d
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+++ b/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.postgres
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+/* Copyright 2020 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.
+ */
+
+-- when we first added the room_version column, it was populated via a background
+-- update. We now need it to be populated before synapse starts, so we populate
+-- any remaining rows with a NULL room version now. For servers which have completed
+-- the background update, this will be pretty quick.
+
+-- the following query will set room_version to NULL if no create event is found for
+-- the room in current_state_events, and will set it to '1' if a create event with no
+-- room_version is found.
+
+UPDATE rooms SET room_version=(
+    SELECT COALESCE(json::json->'content'->>'room_version','1')
+    FROM current_state_events cse INNER JOIN event_json ej USING (event_id)
+    WHERE cse.room_id=rooms.room_id AND cse.type='m.room.create' AND cse.state_key=''
+) WHERE rooms.room_version IS NULL;
+
+-- we still allow the background update to complete: it has the useful side-effect of
+-- populating `rooms` with any missing rooms (based on the current_state_events table).
+
+-- see also rooms_version_column_2.sql.sqlite which has a copy of the above query, using
+-- sqlite syntax for the json extraction.
diff --git a/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.sqlite b/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.sqlite
new file mode 100644
index 000000000..335c6f207
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+++ b/synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_2.sql.sqlite
@@ -0,0 +1,22 @@
+/* Copyright 2020 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.
+ */
+
+-- see rooms_version_column_2.sql.postgres for details of what's going on here.
+
+UPDATE rooms SET room_version=(
+    SELECT COALESCE(json_extract(ej.json, '$.content.room_version'), '1')
+    FROM current_state_events cse INNER JOIN event_json ej USING (event_id)
+    WHERE cse.room_id=rooms.room_id AND cse.type='m.room.create' AND cse.state_key=''
+) WHERE rooms.room_version IS NULL;