Fixed removal of new presence stream states (#10014)

Fixes: https://github.com/matrix-org/synapse/issues/9962

This is a fix for above problem.

I fixed it by swaping the order of insertion of new records and deletion of old ones. This ensures that we don't delete fresh database records as we do deletes before inserts.

Signed-off-by: Marek Matys <themarcq@gmail.com>

changelog.d/10014.bugfix

@@ -0,0 +1 @@
+Fixed deletion of new presence stream states from database. 

synapse/storage/databases/main/presence.py

@@ -97,6 +97,15 @@ class PresenceStore(SQLBaseStore):
             )
             txn.call_after(self._get_presence_for_user.invalidate, (state.user_id,))
 
+        # Delete old rows to stop database from getting really big
+        sql = "DELETE FROM presence_stream WHERE stream_id < ? AND "
+
+        for states in batch_iter(presence_states, 50):
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "user_id", [s.user_id for s in states]
+            )
+            txn.execute(sql + clause, [stream_id] + list(args))
+
         # Actually insert new rows
         self.db_pool.simple_insert_many_txn(
             txn,
@@ -117,15 +126,6 @@ class PresenceStore(SQLBaseStore):
             ],
         )
 
-        # Delete old rows to stop database from getting really big
-        sql = "DELETE FROM presence_stream WHERE stream_id < ? AND "
-
-        for states in batch_iter(presence_states, 50):
-            clause, args = make_in_list_sql_clause(
-                self.database_engine, "user_id", [s.user_id for s in states]
-            )
-            txn.execute(sql + clause, [stream_id] + list(args))
-
     async def get_all_presence_updates(
         self, instance_name: str, last_id: int, current_id: int, limit: int
     ) -> Tuple[List[Tuple[int, list]], int, bool]: