Filter out appservices from mau count (#8404)

This is an attempt to fix #8403.

changelog.d/8404.misc

@@ -0,0 +1 @@
+Do not include appservice users when calculating the total MAU for a server.

synapse/storage/databases/main/monthly_active_users.py

@@ -41,7 +41,14 @@ async def get_monthly_active_count(self) -> int:
         """
 
         def _count_users(txn):
-            sql = "SELECT COALESCE(count(*), 0) FROM monthly_active_users"
+            # Exclude app service users
+            sql = """
+                SELECT COALESCE(count(*), 0)
+                FROM monthly_active_users
+                    LEFT JOIN users
+                    ON monthly_active_users.user_id=users.name
+                WHERE (users.appservice_id IS NULL OR users.appservice_id = '');
+            """
             txn.execute(sql)
             (count,) = txn.fetchone()
             return count

tests/storage/test_monthly_active_users.py

@@ -137,6 +137,21 @@ def test_can_insert_and_count_mau(self):
         count = self.get_success(self.store.get_monthly_active_count())
         self.assertEqual(count, 1)
 
+    def test_appservice_user_not_counted_in_mau(self):
+        self.get_success(
+            self.store.register_user(
+                user_id="@appservice_user:server", appservice_id="wibble"
+            )
+        )
+        count = self.get_success(self.store.get_monthly_active_count())
+        self.assertEqual(count, 0)
+
+        d = self.store.upsert_monthly_active_user("@appservice_user:server")
+        self.get_success(d)
+
+        count = self.get_success(self.store.get_monthly_active_count())
+        self.assertEqual(count, 0)
+
     def test_user_last_seen_monthly_active(self):
         user_id1 = "@user1:server"
         user_id2 = "@user2:server"
@@ -383,7 +398,7 @@ def test_get_monthly_active_count_by_service(self):
         self.get_success(self.store.upsert_monthly_active_user(appservice2_user1))
 
         count = self.get_success(self.store.get_monthly_active_count())
-        self.assertEqual(count, 4)
+        self.assertEqual(count, 1)
 
         d = self.store.get_monthly_active_count_by_service()
         result = self.get_success(d)