Fix slow performance of `/logout` in some cases where refresh tokens are in use. The slowness existed since the initial implementation of refresh tokens. (#12056)

2 files changed, 44 insertions, 2 deletions

diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index 17110bb033..dc6665237a 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -1681,7 +1681,8 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
                 user_id=row[1],
                 device_id=row[2],
                 next_token_id=row[3],
-                has_next_refresh_token_been_refreshed=row[4],
+                # SQLite returns 0 or 1 for false/true, so convert to a bool.
+                has_next_refresh_token_been_refreshed=bool(row[4]),
                 # This column is nullable, ensure it's a boolean
                 has_next_access_token_been_used=(row[5] or False),
                 expiry_ts=row[6],
@@ -1697,12 +1698,15 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
         Set the successor of a refresh token, removing the existing successor
         if any.
 
+        This also deletes the predecessor refresh and access tokens,
+        since they cannot be valid anymore.
+
         Args:
             token_id: ID of the refresh token to update.
             next_token_id: ID of its successor.
         """
 
-        def _replace_refresh_token_txn(txn) -> None:
+        def _replace_refresh_token_txn(txn: LoggingTransaction) -> None:
             # First check if there was an existing refresh token
             old_next_token_id = self.db_pool.simple_select_one_onecol_txn(
                 txn,
@@ -1728,6 +1732,16 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
                     {"id": old_next_token_id},
                 )
 
+            # Delete the previous refresh token, since we only want to keep the
+            # last 2 refresh tokens in the database.
+            # (The predecessor of the latest refresh token is still useful in
+            # case the refresh was interrupted and the client re-uses the old
+            # one.)
+            # This cascades to delete the associated access token.
+            self.db_pool.simple_delete_txn(
+                txn, "refresh_tokens", {"next_token_id": token_id}
+            )
+
         await self.db_pool.runInteraction(
             "replace_refresh_token", _replace_refresh_token_txn
         )
diff --git a/synapse/storage/schema/main/delta/68/04_refresh_tokens_index_next_token_id.sql b/synapse/storage/schema/main/delta/68/04_refresh_tokens_index_next_token_id.sql
new file mode 100644
index 0000000000..09305638ea
--- /dev/null
+++ b/synapse/storage/schema/main/delta/68/04_refresh_tokens_index_next_token_id.sql
@@ -0,0 +1,28 @@
+/* Copyright 2022 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.
+ */
+
+-- next_token_id is a foreign key reference, so previously required a table scan
+-- when a row in the referenced table was deleted.
+-- As it was self-referential and cascaded deletes, this led to O(t*n) time to
+-- delete a row, where t: number of rows in the table and n: number of rows in
+-- the ancestral 'chain' of access tokens.
+--
+-- This index is partial since we only require it for rows which reference
+-- another.
+-- Performance was tested to be the same regardless of whether the index was
+-- full or partial, but a partial index can be smaller.
+CREATE INDEX refresh_tokens_next_token_id
+    ON refresh_tokens(next_token_id)
+    WHERE next_token_id IS NOT NULL;