Add a partial index to presence_stream to speed up startups

changelog.d/10748.misc

@@ -0,0 +1 @@
+Add an index to `presence_stream` to hopefully speed up startups a little.

synapse/storage/databases/main/presence.py

@@ -73,6 +73,15 @@ def __init__(
             prefilled_cache=presence_cache_prefill,
         )
 
+        # Used by `_get_active_presence()`
+        self.db_pool.updates.register_background_index_update(
+            "presence_stream_not_offline_index",
+            index_name="presence_stream_state_not_offline_idx",
+            table="presence_stream",
+            columns=["state"],
+            where_clause="state != 'offline'",
+        )
+
     async def update_presence(self, presence_states):
         assert self._can_persist_presence
 
@@ -332,6 +341,8 @@ def _get_active_presence(self, db_conn: Connection):
         the appropriate time outs.
         """
 
+        # The `presence_stream_state_not_offline_idx` index should be used for this
+        # query.
         sql = (
             "SELECT user_id, state, last_active_ts, last_federation_update_ts,"
             " last_user_sync_ts, status_msg, currently_active FROM presence_stream"

synapse/storage/schema/main/delta/63/04add_presence_stream_not_offline_index.sql

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2021 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.
+ */
+
+INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
+  (6304, 'presence_stream_not_offline_index', '{}');