From d3f01f7ea92e3a3866db4bc4308374fe131630f3 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 9 Jun 2022 17:49:37 -1000
Subject: [PATCH] Reduce memory pressure from history_stats with large data
 sets (#73289)

---
 .../components/history_stats/data.py          | 49 ++++++++++++++-----
 1 file changed, 36 insertions(+), 13 deletions(-)

diff --git a/homeassistant/components/history_stats/data.py b/homeassistant/components/history_stats/data.py
index 3b17c715c97..33f32e72292 100644
--- a/homeassistant/components/history_stats/data.py
+++ b/homeassistant/components/history_stats/data.py
@@ -23,6 +23,14 @@ class HistoryStatsState:
     period: tuple[datetime.datetime, datetime.datetime]
 
 
+@dataclass
+class HistoryState:
+    """A minimal state to avoid holding on to State objects."""
+
+    state: str
+    last_changed: float
+
+
 class HistoryStats:
     """Manage history stats."""
 
@@ -40,7 +48,7 @@ class HistoryStats:
         self.entity_id = entity_id
         self._period = (MIN_TIME_UTC, MIN_TIME_UTC)
         self._state: HistoryStatsState = HistoryStatsState(None, None, self._period)
-        self._history_current_period: list[State] = []
+        self._history_current_period: list[HistoryState] = []
         self._previous_run_before_start = False
         self._entity_states = set(entity_states)
         self._duration = duration
@@ -103,20 +111,18 @@ class HistoryStats:
                     <= floored_timestamp(new_state.last_changed)
                     <= current_period_end_timestamp
                 ):
-                    self._history_current_period.append(new_state)
+                    self._history_current_period.append(
+                        HistoryState(
+                            new_state.state, new_state.last_changed.timestamp()
+                        )
+                    )
                     new_data = True
             if not new_data and current_period_end_timestamp < now_timestamp:
                 # If period has not changed and current time after the period end...
                 # Don't compute anything as the value cannot have changed
                 return self._state
         else:
-            self._history_current_period = await get_instance(
-                self.hass
-            ).async_add_executor_job(
-                self._update_from_database,
-                current_period_start,
-                current_period_end,
-            )
+            await self._async_history_from_db(current_period_start, current_period_end)
             self._previous_run_before_start = False
 
         hours_matched, match_count = self._async_compute_hours_and_changes(
@@ -127,7 +133,24 @@ class HistoryStats:
         self._state = HistoryStatsState(hours_matched, match_count, self._period)
         return self._state
 
-    def _update_from_database(
+    async def _async_history_from_db(
+        self,
+        current_period_start: datetime.datetime,
+        current_period_end: datetime.datetime,
+    ) -> None:
+        """Update history data for the current period from the database."""
+        instance = get_instance(self.hass)
+        states = await instance.async_add_executor_job(
+            self._state_changes_during_period,
+            current_period_start,
+            current_period_end,
+        )
+        self._history_current_period = [
+            HistoryState(state.state, state.last_changed.timestamp())
+            for state in states
+        ]
+
+    def _state_changes_during_period(
         self, start: datetime.datetime, end: datetime.datetime
     ) -> list[State]:
         return history.state_changes_during_period(
@@ -155,9 +178,9 @@ class HistoryStats:
         match_count = 1 if previous_state_matches else 0
 
         # Make calculations
-        for item in self._history_current_period:
-            current_state_matches = item.state in self._entity_states
-            state_change_timestamp = item.last_changed.timestamp()
+        for history_state in self._history_current_period:
+            current_state_matches = history_state.state in self._entity_states
+            state_change_timestamp = history_state.last_changed
 
             if previous_state_matches:
                 elapsed += state_change_timestamp - last_state_change_timestamp