Remove manys calls to cursor_to_dict (#16431)

This avoids calling cursor_to_dict and then immediately
unpacking the values in the dict for other users. By not
creating the intermediate dictionary we can avoid allocating
the dictionary and strings for the keys, which should generally
be more performant.

Additionally this improves type hints by avoid Dict[str, Any]
dictionaries coming out of the database layer.

1 files changed, 7 insertions, 22 deletions

diff --git a/synapse/storage/databases/main/appservice.py b/synapse/storage/databases/main/appservice.py

index 0553a0621a..073a99cd84 100644
--- a/synapse/storage/databases/main/appservice.py
+++ b/synapse/storage/databases/main/appservice.py
@@ -14,17 +14,7 @@
 # limitations under the License.
 import logging
 import re
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Dict,
-    List,
-    Optional,
-    Pattern,
-    Sequence,
-    Tuple,
-    cast,
-)
+from typing import TYPE_CHECKING, List, Optional, Pattern, Sequence, Tuple, cast
 
 from synapse.appservice import (
     ApplicationService,
@@ -353,21 +343,15 @@ class ApplicationServiceTransactionWorkerStore(
 
         def _get_oldest_unsent_txn(
             txn: LoggingTransaction,
-        ) -> Optional[Dict[str, Any]]:
+        ) -> Optional[Tuple[int, str]]:
             # Monotonically increasing txn ids, so just select the smallest
             # one in the txns table (we delete them when they are sent)
             txn.execute(
-                "SELECT * FROM application_services_txns WHERE as_id=?"
+                "SELECT txn_id, event_ids FROM application_services_txns WHERE as_id=?"
                 " ORDER BY txn_id ASC LIMIT 1",
                 (service.id,),
             )
-            rows = self.db_pool.cursor_to_dict(txn)
-            if not rows:
-                return None
-
-            entry = rows[0]
-
-            return entry
+            return cast(Optional[Tuple[int, str]], txn.fetchone())
 
         entry = await self.db_pool.runInteraction(
             "get_oldest_unsent_appservice_txn", _get_oldest_unsent_txn
@@ -376,8 +360,9 @@ class ApplicationServiceTransactionWorkerStore(
         if not entry:
             return None
 
-        event_ids = db_to_json(entry["event_ids"])
+        txn_id, event_ids_str = entry
 
+        event_ids = db_to_json(event_ids_str)
         events = await self.get_events_as_list(event_ids)
 
         # TODO: to-device messages, one-time key counts, device list summaries and unused
@@ -385,7 +370,7 @@ class ApplicationServiceTransactionWorkerStore(
         #       We likely want to populate those for reliability.
         return AppServiceTransaction(
             service=service,
-            id=entry["txn_id"],
+            id=txn_id,
             events=events,
             ephemeral=[],
             to_device_messages=[],