From bf974e103e651a1334493a9594e08d19e51e392b Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Tue, 11 Apr 2023 08:52:38 -1000
Subject: [PATCH] reverse later is faster because the index is in forward order
 and the data size we are reversing is much smaller even if we are in python
 code

---
 .../components/recorder/history/modern.py     | 51 +++++++++----------
 1 file changed, 25 insertions(+), 26 deletions(-)

diff --git a/homeassistant/components/recorder/history/modern.py b/homeassistant/components/recorder/history/modern.py
index d48c7a0de9a..101eb01caa4 100644
--- a/homeassistant/components/recorder/history/modern.py
+++ b/homeassistant/components/recorder/history/modern.py
@@ -321,7 +321,6 @@ def _state_changed_during_period_stmt(
     end_time_ts: float | None,
     single_metadata_id: int,
     no_attributes: bool,
-    descending: bool,
     limit: int | None,
     include_start_time_state: bool,
     run_start_ts: float | None,
@@ -348,32 +347,28 @@ def _state_changed_during_period_stmt(
     if not include_start_time_state or not run_start_ts:
         return stmt.order_by(
             States.metadata_id,
-            States.last_updated_ts.desc() if descending else States.last_updated_ts,
+            States.last_updated_ts,
         )
-
-    union_subquery = union_all(
-        _select_from_subquery(
-            _get_single_entity_start_time_stmt(
-                start_time_ts,
-                single_metadata_id,
+    return _select_from_subquery(
+        union_all(
+            _select_from_subquery(
+                _get_single_entity_start_time_stmt(
+                    start_time_ts,
+                    single_metadata_id,
+                    no_attributes,
+                    False,
+                ).subquery(),
                 no_attributes,
                 False,
-            ).subquery(),
-            no_attributes,
-            False,
-        ),
-        _select_from_subquery(
-            stmt.order_by(States.metadata_id, States.last_updated_ts).subquery(),
-            no_attributes,
-            False,
-        ),
-    ).subquery()
-    stmt = _select_from_subquery(union_subquery, no_attributes, False)
-    if not descending:
-        return stmt
-    # If descending, we need to reverse the results
-    return stmt.order_by(
-        union_subquery.c.metadata_id, union_subquery.c.last_updated_ts.desc()
+            ),
+            _select_from_subquery(
+                stmt.subquery(),
+                no_attributes,
+                False,
+            ),
+        ).subquery(),
+        no_attributes,
+        False,
     )
 
 
@@ -417,7 +412,6 @@ def state_changes_during_period(
                 end_time_ts,
                 single_metadata_id,
                 no_attributes,
-                descending,
                 limit,
                 include_start_time_state,
                 run_start_ts,
@@ -425,7 +419,6 @@ def state_changes_during_period(
             track_on=[
                 bool(end_time_ts),
                 no_attributes,
-                descending,
                 bool(limit),
                 include_start_time_state,
             ],
@@ -437,6 +430,7 @@ def state_changes_during_period(
                 start_time_ts if include_start_time_state else None,
                 entity_ids,
                 entity_id_to_metadata_id,
+                descending=descending,
             ),
         )
 
@@ -654,6 +648,7 @@ def _sorted_states_to_dict(
     entity_id_to_metadata_id: dict[str, int | None],
     minimal_response: bool = False,
     compressed_state_format: bool = False,
+    descending: bool = False,
 ) -> MutableMapping[str, list[State | dict[str, Any]]]:
     """Convert SQL results into JSON friendly data structure.
 
@@ -778,5 +773,9 @@ def _sorted_states_to_dict(
             if (state := row[state_idx]) != prev_state
         )
 
+    if descending:
+        for ent_results in result.values():
+            ent_results.reverse()
+
     # Filter out the empty lists if some states had 0 results.
     return {key: val for key, val in result.items() if val}