Use receipts `event_stream_ordering` instead of joins (#17032)

Resurrecting https://github.com/matrix-org/synapse/pull/13918.

This should reduce IOPs incurred by joining to the events table to
lookup stream ordering, which happens in many receipt handling code
paths. Like the previous PR I believe sufficient time has passed between
the original migration in DB schema 72 and now to merge this as-is. It's
highly unlikely that both the migration is still ongoing AND (active)
users still have any receipts prior to that date.

In the unlikely event there is a receipt without a populated
`event_stream_ordering` synapse will behave just as it does now when
receipts exist for events that don't (yet): for push action calculation
the receipts are just ignored.

I've removed the validation on event IDs as this is already covered
here:

https://github.com/element-hq/synapse/blob/59ceabcb9798793cd4312fdbcced4e612aeda84d/synapse/handlers/receipts.py#L189-L192

3 files changed, 12 insertions, 19 deletions

diff --git a/changelog.d/17032.misc b/changelog.d/17032.misc
new file mode 100644
index 0000000000..b03f6f42e5
--- /dev/null
+++ b/changelog.d/17032.misc
@@ -0,0 +1 @@
+Use new receipts column to optimise receipt and push action SQL queries. Contributed by Nick @ Beeper (@fizzadar).
diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index 40bf000e9c..bdd0781c48 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -385,7 +385,6 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
             WITH all_receipts AS (
                 SELECT room_id, thread_id, MAX(event_stream_ordering) AS max_receipt_stream_ordering
                 FROM receipts_linearized
-                LEFT JOIN events USING (room_id, event_id)
                 WHERE
                     {receipt_types_clause}
                     AND user_id = ?
@@ -621,13 +620,12 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
                 SELECT notif_count, COALESCE(unread_count, 0), thread_id
                 FROM event_push_summary
                 LEFT JOIN (
-                    SELECT thread_id, MAX(stream_ordering) AS threaded_receipt_stream_ordering
+                    SELECT thread_id, MAX(event_stream_ordering) AS threaded_receipt_stream_ordering
                     FROM receipts_linearized
-                    LEFT JOIN events USING (room_id, event_id)
                     WHERE
                         user_id = ?
                         AND room_id = ?
-                        AND stream_ordering > ?
+                        AND event_stream_ordering > ?
                         AND {receipt_types_clause}
                     GROUP BY thread_id
                 ) AS receipts USING (thread_id)
@@ -659,13 +657,12 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
         sql = f"""
             SELECT COUNT(*), thread_id FROM event_push_actions
             LEFT JOIN (
-                SELECT thread_id, MAX(stream_ordering) AS threaded_receipt_stream_ordering
+                SELECT thread_id, MAX(event_stream_ordering) AS threaded_receipt_stream_ordering
                 FROM receipts_linearized
-                LEFT JOIN events USING (room_id, event_id)
                 WHERE
                     user_id = ?
                     AND room_id = ?
-                    AND stream_ordering > ?
+                    AND event_stream_ordering > ?
                     AND {receipt_types_clause}
                 GROUP BY thread_id
             ) AS receipts USING (thread_id)
@@ -738,13 +735,12 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
                 thread_id
             FROM event_push_actions
             LEFT JOIN (
-                SELECT thread_id, MAX(stream_ordering) AS threaded_receipt_stream_ordering
+                SELECT thread_id, MAX(event_stream_ordering) AS threaded_receipt_stream_ordering
                 FROM receipts_linearized
-                LEFT JOIN events USING (room_id, event_id)
                 WHERE
                     user_id = ?
                     AND room_id = ?
-                    AND stream_ordering > ?
+                    AND event_stream_ordering > ?
                     AND {receipt_types_clause}
                 GROUP BY thread_id
             ) AS receipts USING (thread_id)
@@ -910,9 +906,8 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
         # given this function generally gets called with only one room and
         # thread ID.
         sql = f"""
-            SELECT room_id, thread_id, MAX(stream_ordering)
+            SELECT room_id, thread_id, MAX(event_stream_ordering)
             FROM receipts_linearized
-            INNER JOIN events USING (room_id, event_id)
             WHERE {receipt_types_clause}
                 AND {thread_ids_clause}
                 AND {room_ids_clause}
@@ -1442,9 +1437,8 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
         )
 
         sql = """
-            SELECT r.stream_id, r.room_id, r.user_id, r.thread_id, e.stream_ordering
+            SELECT r.stream_id, r.room_id, r.user_id, r.thread_id, r.event_stream_ordering
             FROM receipts_linearized AS r
-            INNER JOIN events AS e USING (event_id)
             WHERE ? < r.stream_id AND r.stream_id <= ? AND user_id LIKE ?
             ORDER BY r.stream_id ASC
             LIMIT ?
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index d513c42530..9660fc4699 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -178,14 +178,13 @@ class ReceiptsWorkerStore(SQLBaseStore):
         )
 
         sql = f"""
-            SELECT event_id, stream_ordering
+            SELECT event_id, event_stream_ordering
             FROM receipts_linearized
-            INNER JOIN events USING (room_id, event_id)
             WHERE {clause}
             AND user_id = ?
             AND room_id = ?
             AND thread_id IS NULL
-            ORDER BY stream_ordering DESC
+            ORDER BY event_stream_ordering DESC
             LIMIT 1
         """
 
@@ -736,8 +735,7 @@ class ReceiptsWorkerStore(SQLBaseStore):
                 thread_args = (thread_id,)
 
             sql = f"""
-            SELECT stream_ordering, event_id FROM events
-            INNER JOIN receipts_linearized AS r USING (event_id, room_id)
+            SELECT r.event_stream_ordering, r.event_id FROM receipts_linearized AS r
             WHERE r.room_id = ? AND r.receipt_type = ? AND r.user_id = ? AND {thread_clause}
             """
             txn.execute(