Convert simple_select_list_paginate_txn to return tuples. (#16433)

7 files changed, 67 insertions, 39 deletions

diff --git a/changelog.d/16433.misc b/changelog.d/16433.misc
new file mode 100644
index 0000000000..bd7cdd42af
--- /dev/null
+++ b/changelog.d/16433.misc
@@ -0,0 +1 @@
+Reduce memory allocations.
diff --git a/synapse/api/presence.py b/synapse/api/presence.py
index b78f419994..afef6712e1 100644
--- a/synapse/api/presence.py
+++ b/synapse/api/presence.py
@@ -80,10 +80,6 @@ class UserPresenceState:
     def as_dict(self) -> JsonDict:
         return attr.asdict(self)
 
-    @staticmethod
-    def from_dict(d: JsonDict) -> "UserPresenceState":
-        return UserPresenceState(**d)
-
     def copy_and_replace(self, **kwargs: Any) -> "UserPresenceState":
         return attr.evolve(self, **kwargs)
 
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index 6520795635..525968bcba 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -395,7 +395,7 @@ class PresenceDestinationsRow(BaseFederationRow):
     @staticmethod
     def from_data(data: JsonDict) -> "PresenceDestinationsRow":
         return PresenceDestinationsRow(
-            state=UserPresenceState.from_dict(data["state"]), destinations=data["dests"]
+            state=UserPresenceState(**data["state"]), destinations=data["dests"]
         )
 
     def to_data(self) -> JsonDict:
diff --git a/synapse/rest/admin/federation.py b/synapse/rest/admin/federation.py
index e0ee55bd0e..8a617af599 100644
--- a/synapse/rest/admin/federation.py
+++ b/synapse/rest/admin/federation.py
@@ -198,7 +198,13 @@ class DestinationMembershipRestServlet(RestServlet):
         rooms, total = await self._store.get_destination_rooms_paginate(
             destination, start, limit, direction
         )
-        response = {"rooms": rooms, "total": total}
+        response = {
+            "rooms": [
+                {"room_id": room_id, "stream_ordering": stream_ordering}
+                for room_id, stream_ordering in rooms
+            ],
+            "total": total,
+        }
         if (start + limit) < total:
             response["next_token"] = str(start + len(rooms))
 
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index ca894edd5a..7d8af5c610 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -2418,7 +2418,7 @@ class DatabasePool:
         keyvalues: Optional[Dict[str, Any]] = None,
         exclude_keyvalues: Optional[Dict[str, Any]] = None,
         order_direction: str = "ASC",
-    ) -> List[Dict[str, Any]]:
+    ) -> List[Tuple[Any, ...]]:
         """
         Executes a SELECT query on the named table with start and limit,
         of row numbers, which may return zero or number of rows from start to limit,
@@ -2447,7 +2447,7 @@ class DatabasePool:
             order_direction: Whether the results should be ordered "ASC" or "DESC".
 
         Returns:
-            The result as a list of dictionaries.
+            The result as a list of tuples.
         """
         if order_direction not in ["ASC", "DESC"]:
             raise ValueError("order_direction must be one of 'ASC' or 'DESC'.")
@@ -2474,7 +2474,7 @@ class DatabasePool:
         )
         txn.execute(sql, arg_list + [limit, start])
 
-        return cls.cursor_to_dict(txn)
+        return txn.fetchall()
 
     async def simple_search_list(
         self,
diff --git a/synapse/storage/databases/main/presence.py b/synapse/storage/databases/main/presence.py
index 805c23f89f..519f05fb60 100644
--- a/synapse/storage/databases/main/presence.py
+++ b/synapse/storage/databases/main/presence.py
@@ -20,6 +20,7 @@ from typing import (
     Mapping,
     Optional,
     Tuple,
+    Union,
     cast,
 )
 
@@ -385,28 +386,47 @@ class PresenceStore(PresenceBackgroundUpdateStore, CacheInvalidationWorkerStore)
         limit = 100
         offset = 0
         while True:
-            rows = await self.db_pool.runInteraction(
-                "get_presence_for_all_users",
-                self.db_pool.simple_select_list_paginate_txn,
-                "presence_stream",
-                orderby="stream_id",
-                start=offset,
-                limit=limit,
-                exclude_keyvalues=exclude_keyvalues,
-                retcols=(
-                    "user_id",
-                    "state",
-                    "last_active_ts",
-                    "last_federation_update_ts",
-                    "last_user_sync_ts",
-                    "status_msg",
-                    "currently_active",
+            rows = cast(
+                List[Tuple[str, str, int, int, int, Optional[str], Union[int, bool]]],
+                await self.db_pool.runInteraction(
+                    "get_presence_for_all_users",
+                    self.db_pool.simple_select_list_paginate_txn,
+                    "presence_stream",
+                    orderby="stream_id",
+                    start=offset,
+                    limit=limit,
+                    exclude_keyvalues=exclude_keyvalues,
+                    retcols=(
+                        "user_id",
+                        "state",
+                        "last_active_ts",
+                        "last_federation_update_ts",
+                        "last_user_sync_ts",
+                        "status_msg",
+                        "currently_active",
+                    ),
+                    order_direction="ASC",
                 ),
-                order_direction="ASC",
             )
 
-            for row in rows:
-                users_to_state[row["user_id"]] = UserPresenceState(**row)
+            for (
+                user_id,
+                state,
+                last_active_ts,
+                last_federation_update_ts,
+                last_user_sync_ts,
+                status_msg,
+                currently_active,
+            ) in rows:
+                users_to_state[user_id] = UserPresenceState(
+                    user_id=user_id,
+                    state=state,
+                    last_active_ts=last_active_ts,
+                    last_federation_update_ts=last_federation_update_ts,
+                    last_user_sync_ts=last_user_sync_ts,
+                    status_msg=status_msg,
+                    currently_active=bool(currently_active),
+                )
 
             # We've run out of updates to query
             if len(rows) < limit:
diff --git a/synapse/storage/databases/main/transactions.py b/synapse/storage/databases/main/transactions.py
index 8f70eff809..f35757280d 100644
--- a/synapse/storage/databases/main/transactions.py
+++ b/synapse/storage/databases/main/transactions.py
@@ -526,7 +526,7 @@ class TransactionWorkerStore(CacheInvalidationWorkerStore):
         start: int,
         limit: int,
         direction: Direction = Direction.FORWARDS,
-    ) -> Tuple[List[JsonDict], int]:
+    ) -> Tuple[List[Tuple[str, int]], int]:
         """Function to retrieve a paginated list of destination's rooms.
         This will return a json list of rooms and the
         total number of rooms.
@@ -537,12 +537,14 @@ class TransactionWorkerStore(CacheInvalidationWorkerStore):
             limit: number of rows to retrieve
             direction: sort ascending or descending by room_id
         Returns:
-            A tuple of a dict of rooms and a count of total rooms.
+            A tuple of a list of room tuples and a count of total rooms.
+
+            Each room tuple is room_id, stream_ordering.
         """
 
         def get_destination_rooms_paginate_txn(
             txn: LoggingTransaction,
-        ) -> Tuple[List[JsonDict], int]:
+        ) -> Tuple[List[Tuple[str, int]], int]:
             if direction == Direction.BACKWARDS:
                 order = "DESC"
             else:
@@ -556,14 +558,17 @@ class TransactionWorkerStore(CacheInvalidationWorkerStore):
             txn.execute(sql, [destination])
             count = cast(Tuple[int], txn.fetchone())[0]
 
-            rooms = self.db_pool.simple_select_list_paginate_txn(
-                txn=txn,
-                table="destination_rooms",
-                orderby="room_id",
-                start=start,
-                limit=limit,
-                retcols=("room_id", "stream_ordering"),
-                order_direction=order,
+            rooms = cast(
+                List[Tuple[str, int]],
+                self.db_pool.simple_select_list_paginate_txn(
+                    txn=txn,
+                    table="destination_rooms",
+                    orderby="room_id",
+                    start=start,
+                    limit=limit,
+                    retcols=("room_id", "stream_ordering"),
+                    order_direction=order,
+                ),
             )
             return rooms, count