Avoid locking for upsert on pushers tables

* replace the upsert into deleted_pushers with an insert
* no need to lock for upsert on pusher_throttle

synapse/storage/pusher.py

@@ -244,11 +244,19 @@ class PusherStore(SQLBaseStore):
                 "pushers",
                 {"app_id": app_id, "pushkey": pushkey, "user_name": user_id}
             )
-            self._simple_upsert_txn(
+
+            # it's possible for us to end up with duplicate rows for
+            # (app_id, pushkey, user_id) at different stream_ids, but that
+            # doesn't really matter.
+            self._simple_insert_txn(
                 txn,
-                "deleted_pushers",
-                {"app_id": app_id, "pushkey": pushkey, "user_id": user_id},
-                {"stream_id": stream_id},
+                table="deleted_pushers",
+                values={
+                    "stream_id": stream_id,
+                    "app_id": app_id,
+                    "pushkey": pushkey,
+                    "user_id": user_id,
+                },
             )
 
         with self._pushers_id_gen.get_next() as stream_id:
@@ -311,9 +319,12 @@ class PusherStore(SQLBaseStore):
 
     @defer.inlineCallbacks
     def set_throttle_params(self, pusher_id, room_id, params):
+        # no need to lock because `pusher_throttle` has a primary key on
+        # (pusher, room_id) so _simple_upsert will retry
         yield self._simple_upsert(
             "pusher_throttle",
             {"pusher": pusher_id, "room_id": room_id},
             params,
-            desc="set_throttle_params"
+            desc="set_throttle_params",
+            lock=False,
         )

synapse/storage/schema/delta/46/drop_unique_deleted_pushers.sql

+/* Copyright 2017 New Vector Ltd
+ *
+ * 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.
+ */
+
+-- drop the unique constraint on deleted_pushers so that we can just insert
+-- into it rather than upserting.
+
+CREATE TABLE deleted_pushers2 (
+    stream_id BIGINT NOT NULL,
+    app_id TEXT NOT NULL,
+    pushkey TEXT NOT NULL,
+    user_id TEXT NOT NULL
+);
+
+INSERT INTO deleted_pushers2 (stream_id, app_id, pushkey, user_id)
+    SELECT stream_id, app_id, pushkey, user_id from deleted_pushers;
+
+DROP TABLE deleted_pushers;
+ALTER TABLE deleted_pushers2 RENAME TO deleted_pushers;
+
+-- create the index after doing the inserts because that's more efficient.
+-- it also means we can give it the same name as the old one without renaming.
+CREATE INDEX deleted_pushers_stream_id ON deleted_pushers (stream_id);
+