From 35dc21f981bea00ae84872cd6347655e168b3481 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Mon, 17 Jan 2022 17:10:36 +0000
Subject: [PATCH] Create singletons for `StateFilter.{all,none}()`

No point recreating these for each call, since they are frozen
---
 changelog.d/11836.misc   |  1 +
 synapse/storage/state.py | 14 +++++++++-----
 2 files changed, 10 insertions(+), 5 deletions(-)
 create mode 100644 changelog.d/11836.misc

diff --git a/changelog.d/11836.misc b/changelog.d/11836.misc
new file mode 100644
index 000000000000..be7e331c639c
--- /dev/null
+++ b/changelog.d/11836.misc
@@ -0,0 +1 @@
+Minor performance improvement in room state lookup.
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index df8b2f108877..913448f0f95e 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -74,21 +74,21 @@ def __attrs_post_init__(self):
 
     @staticmethod
     def all() -> "StateFilter":
-        """Creates a filter that fetches everything.
+        """Returns a filter that fetches everything.
 
         Returns:
-            The new state filter.
+            The state filter.
         """
-        return StateFilter(types=frozendict(), include_others=True)
+        return _ALL_STATE_FILTER
 
     @staticmethod
     def none() -> "StateFilter":
-        """Creates a filter that fetches nothing.
+        """Returns a filter that fetches nothing.
 
         Returns:
             The new state filter.
         """
-        return StateFilter(types=frozendict(), include_others=False)
+        return _NONE_STATE_FILTER
 
     @staticmethod
     def from_types(types: Iterable[Tuple[str, Optional[str]]]) -> "StateFilter":
@@ -527,6 +527,10 @@ def approx_difference(self, other: "StateFilter") -> "StateFilter":
         )
 
 
+_ALL_STATE_FILTER = StateFilter(types=frozendict(), include_others=True)
+_NONE_STATE_FILTER = StateFilter(types=frozendict(), include_others=False)
+
+
 class StateGroupStorage:
     """High level interface to fetching state for event."""