Reintroduce membership tables event stream ordering (#15128)

* Add `event_stream_ordering` column to membership state tables

Specifically this adds the column to `current_state_events`,
`local_current_membership` and `room_memberships`. Each of these tables
is regularly joined with the `events` table to get the stream ordering
and denormalising this into each table will yield significant query
performance improvements once used.

* Make denormalised `event_stream_ordering` columns foreign keys
* Add comment in schema file explaining new denormalised columns
* Add triggers to enforce consistency of `event_stream_ordering` columns
* Re-order purge room tables to account for foreign keys
* Bump schema version to 75

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

6 files changed, 131 insertions, 12 deletions

diff --git a/changelog.d/15128.misc b/changelog.d/15128.misc
new file mode 100644
index 0000000000..c09911e48d
--- /dev/null
+++ b/changelog.d/15128.misc
@@ -0,0 +1 @@
+Add denormalised event stream ordering column to membership state tables for future use. Contributed by Nick @ Beeper (@fizzadar).
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index a8a4ed4436..193959b250 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -1126,11 +1126,15 @@ class PersistEventsStore:
                 # been inserted into room_memberships.
                 txn.execute_batch(
                     """INSERT INTO current_state_events
-                        (room_id, type, state_key, event_id, membership)
-                    VALUES (?, ?, ?, ?, (SELECT membership FROM room_memberships WHERE event_id = ?))
+                        (room_id, type, state_key, event_id, membership, event_stream_ordering)
+                    VALUES (
+                        ?, ?, ?, ?,
+                        (SELECT membership FROM room_memberships WHERE event_id = ?),
+                        (SELECT stream_ordering FROM events WHERE event_id = ?)
+                    )
                     """,
                     [
-                        (room_id, key[0], key[1], ev_id, ev_id)
+                        (room_id, key[0], key[1], ev_id, ev_id, ev_id)
                         for key, ev_id in to_insert.items()
                     ],
                 )
@@ -1157,11 +1161,15 @@ class PersistEventsStore:
             if to_insert:
                 txn.execute_batch(
                     """INSERT INTO local_current_membership
-                        (room_id, user_id, event_id, membership)
-                    VALUES (?, ?, ?, (SELECT membership FROM room_memberships WHERE event_id = ?))
+                        (room_id, user_id, event_id, membership, event_stream_ordering)
+                    VALUES (
+                        ?, ?, ?,
+                        (SELECT membership FROM room_memberships WHERE event_id = ?),
+                        (SELECT stream_ordering FROM events WHERE event_id = ?)
+                    )
                     """,
                     [
-                        (room_id, key[1], ev_id, ev_id)
+                        (room_id, key[1], ev_id, ev_id, ev_id)
                         for key, ev_id in to_insert.items()
                         if key[0] == EventTypes.Member and self.is_mine_id(key[1])
                     ],
@@ -1769,6 +1777,7 @@ class PersistEventsStore:
             table="room_memberships",
             keys=(
                 "event_id",
+                "event_stream_ordering",
                 "user_id",
                 "sender",
                 "room_id",
@@ -1779,6 +1788,7 @@ class PersistEventsStore:
             values=[
                 (
                     event.event_id,
+                    event.internal_metadata.stream_ordering,
                     event.state_key,
                     event.user_id,
                     event.room_id,
@@ -1811,6 +1821,7 @@ class PersistEventsStore:
                     keyvalues={"room_id": event.room_id, "user_id": event.state_key},
                     values={
                         "event_id": event.event_id,
+                        "event_stream_ordering": event.internal_metadata.stream_ordering,
                         "membership": event.membership,
                     },
                 )
diff --git a/synapse/storage/databases/main/purge_events.py b/synapse/storage/databases/main/purge_events.py
index 7a7c0d9c75..efbd3e75d9 100644
--- a/synapse/storage/databases/main/purge_events.py
+++ b/synapse/storage/databases/main/purge_events.py
@@ -428,14 +428,16 @@ class PurgeEventsStore(StateGroupWorkerStore, CacheInvalidationWorkerStore):
             "partial_state_events",
             "partial_state_rooms_servers",
             "partial_state_rooms",
+            # Note: the _membership(s) tables have foreign keys to the `events` table
+            # so must be deleted first.
+            "local_current_membership",
+            "room_memberships",
             "events",
             "federation_inbound_events_staging",
-            "local_current_membership",
             "receipts_graph",
             "receipts_linearized",
             "room_aliases",
             "room_depth",
-            "room_memberships",
             "room_stats_state",
             "room_stats_current",
             "room_stats_earliest_token",
diff --git a/synapse/storage/schema/__init__.py b/synapse/storage/schema/__init__.py
index d3103a6c7a..a28f2b997c 100644
--- a/synapse/storage/schema/__init__.py
+++ b/synapse/storage/schema/__init__.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-SCHEMA_VERSION = 74  # remember to update the list below when updating
+SCHEMA_VERSION = 75  # remember to update the list below when updating
 """Represents the expectations made by the codebase about the database schema
 
 This should be incremented whenever the codebase changes its requirements on the
@@ -91,13 +91,19 @@ Changes in SCHEMA_VERSION = 74:
     - A query on `event_stream_ordering` column has now been disambiguated (i.e. the
       codebase can handle the `current_state_events`, `local_current_memberships` and
       `room_memberships` tables having an `event_stream_ordering` column).
+
+Changes in SCHEMA_VERSION = 75:
+    - The `event_stream_ordering` column in membership tables (`current_state_events`,
+      `local_current_membership` & `room_memberships`) is now being populated for new
+      rows. When the background job to populate historical rows lands this will
+      become the compat schema version.
 """
 
 
 SCHEMA_COMPAT_VERSION = (
-    # The threads_id column must exist for event_push_actions, event_push_summary,
-    # receipts_linearized, and receipts_graph.
-    73
+    # Queries against `event_stream_ordering` columns in membership tables must
+    # be disambiguated.
+    74
 )
 """Limit on how far the synapse codebase can be rolled back without breaking db compat
 
diff --git a/synapse/storage/schema/main/delta/74/01membership_tables_event_stream_ordering.sql b/synapse/storage/schema/main/delta/74/01membership_tables_event_stream_ordering.sql
new file mode 100644
index 0000000000..e2608f3a2e
--- /dev/null
+++ b/synapse/storage/schema/main/delta/74/01membership_tables_event_stream_ordering.sql
@@ -0,0 +1,20 @@
+/* Copyright 2022 Beeper
+ *
+ * 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.
+ */
+
+-- Each of these are denormalised copies of `stream_ordering` from the corresponding row in` events` which
+-- we use to improve database performance by reduring JOINs.
+ALTER TABLE current_state_events ADD COLUMN event_stream_ordering BIGINT REFERENCES events(stream_ordering);
+ALTER TABLE local_current_membership ADD COLUMN event_stream_ordering BIGINT REFERENCES events(stream_ordering);
+ALTER TABLE room_memberships ADD COLUMN event_stream_ordering BIGINT REFERENCES events(stream_ordering);
diff --git a/synapse/storage/schema/main/delta/74/02membership_tables_event_stream_ordering_triggers.py b/synapse/storage/schema/main/delta/74/02membership_tables_event_stream_ordering_triggers.py
new file mode 100644
index 0000000000..e32e9083b3
--- /dev/null
+++ b/synapse/storage/schema/main/delta/74/02membership_tables_event_stream_ordering_triggers.py
@@ -0,0 +1,79 @@
+# Copyright 2022 Beeper
+#
+# 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.
+
+
+"""
+This migration adds triggers to the room membership tables to enforce consistency.
+Triggers cannot be expressed in .sql files, so we have to use a separate file.
+"""
+from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine, Sqlite3Engine
+from synapse.storage.types import Cursor
+
+
+def run_create(cur: Cursor, database_engine: BaseDatabaseEngine, *args, **kwargs):
+    # Complain if the `event_stream_ordering` in membership tables doesn't match
+    # the `stream_ordering` row with the same `event_id` in `events`.
+    if isinstance(database_engine, Sqlite3Engine):
+        for table in (
+            "current_state_events",
+            "local_current_membership",
+            "room_memberships",
+        ):
+            cur.execute(
+                f"""
+                CREATE TRIGGER IF NOT EXISTS {table}_bad_event_stream_ordering
+                BEFORE INSERT ON {table}
+                FOR EACH ROW
+                BEGIN
+                    SELECT RAISE(ABORT, 'Incorrect event_stream_ordering in {table}')
+                    WHERE EXISTS (
+                        SELECT 1 FROM events
+                        WHERE events.event_id = NEW.event_id
+                           AND events.stream_ordering != NEW.event_stream_ordering
+                    );
+                END;
+                """
+            )
+    elif isinstance(database_engine, PostgresEngine):
+        cur.execute(
+            """
+            CREATE OR REPLACE FUNCTION check_event_stream_ordering() RETURNS trigger AS $BODY$
+            BEGIN
+                IF EXISTS (
+                    SELECT 1 FROM events
+                    WHERE events.event_id = NEW.event_id
+                       AND events.stream_ordering != NEW.event_stream_ordering
+                ) THEN
+                    RAISE EXCEPTION 'Incorrect event_stream_ordering';
+                END IF;
+                RETURN NEW;
+            END;
+            $BODY$ LANGUAGE plpgsql;
+            """
+        )
+
+        for table in (
+            "current_state_events",
+            "local_current_membership",
+            "room_memberships",
+        ):
+            cur.execute(
+                f"""
+                CREATE TRIGGER check_event_stream_ordering BEFORE INSERT OR UPDATE ON {table}
+                FOR EACH ROW
+                EXECUTE PROCEDURE check_event_stream_ordering()
+                """
+            )
+    else:
+        raise NotImplementedError("Unknown database engine")