Include user agent in user daily visits table (#8503)

Include user agent in user daily visits table.

changelog.d/8503.misc

@@ -0,0 +1 @@
+Add user agent to user_daily_visits table.

synapse/storage/databases/main/metrics.py

@@ -281,9 +281,14 @@ def _generate_user_daily_visits(txn):
             a_day_in_milliseconds = 24 * 60 * 60 * 1000
             now = self._clock.time_msec()
 
+            # A note on user_agent. Technically a given device can have multiple
+            # user agents, so we need to decide which one to pick. We could have handled this
+            # in number of ways, but given that we don't _that_ much have gone for MAX()
+            # For more details of the other options considered see
+            # https://github.com/matrix-org/synapse/pull/8503#discussion_r502306111
             sql = """
-                INSERT INTO user_daily_visits (user_id, device_id, timestamp)
-                    SELECT u.user_id, u.device_id, ?
+                INSERT INTO user_daily_visits (user_id, device_id, timestamp, user_agent)
+                    SELECT u.user_id, u.device_id, ?, MAX(u.user_agent)
                     FROM user_ips AS u
                     LEFT JOIN (
                       SELECT user_id, device_id, timestamp FROM user_daily_visits
@@ -294,7 +299,7 @@ def _generate_user_daily_visits(txn):
                     WHERE last_seen > ? AND last_seen <= ?
                     AND udv.timestamp IS NULL AND users.is_guest=0
                     AND users.appservice_id IS NULL
-                    GROUP BY u.user_id, u.device_id
+                    GROUP BY u.user_id, u.device_id, u.user_agent
             """
 
             # This means that the day has rolled over but there could still

synapse/storage/databases/main/schema/delta/58/20user_daily_visits.sql

@@ -0,0 +1,18 @@
+/* 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.
+ */
+
+ -- Add new column to user_daily_visits to track user agent
+ALTER TABLE user_daily_visits
+    ADD COLUMN user_agent TEXT;