From 3d8a1109085d41d959a4e5d756b002ab2a1c63fe Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Wed, 3 Apr 2024 09:36:57 -1000
Subject: [PATCH] Dispatch the same ReceiveMessage object if the subscription
 topic is the same (#114769)

---
 homeassistant/components/mqtt/client.py | 20 ++++++++++++++------
 homeassistant/components/mqtt/models.py |  2 +-
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/homeassistant/components/mqtt/client.py b/homeassistant/components/mqtt/client.py
index b2fab355c41..83830de4963 100644
--- a/homeassistant/components/mqtt/client.py
+++ b/homeassistant/components/mqtt/client.py
@@ -835,6 +835,7 @@ class MQTT:
         timestamp = dt_util.utcnow()
 
         subscriptions = self._matching_subscriptions(topic)
+        msg_cache_by_subscription_topic: dict[str, ReceiveMessage] = {}
 
         for subscription in subscriptions:
             if msg.retain:
@@ -858,17 +859,24 @@ class MQTT:
                         subscription.job,
                     )
                     continue
-            self.hass.async_run_hass_job(
-                subscription.job,
-                ReceiveMessage(
+            subscription_topic = subscription.topic
+            if subscription_topic not in msg_cache_by_subscription_topic:
+                # Only make one copy of the message
+                # per topic so we avoid storing a separate
+                # dataclass in memory for each subscriber
+                # to the same topic for retained messages
+                receive_msg = ReceiveMessage(
                     topic,
                     payload,
                     msg.qos,
                     msg.retain,
-                    subscription.topic,
+                    subscription_topic,
                     timestamp,
-                ),
-            )
+                )
+                msg_cache_by_subscription_topic[subscription_topic] = receive_msg
+            else:
+                receive_msg = msg_cache_by_subscription_topic[subscription_topic]
+            self.hass.async_run_hass_job(subscription.job, receive_msg)
         self._mqtt_data.state_write_requests.process_write_state_requests(msg)
 
     def _mqtt_on_callback(
diff --git a/homeassistant/components/mqtt/models.py b/homeassistant/components/mqtt/models.py
index 6e6ae784eec..f53643268e7 100644
--- a/homeassistant/components/mqtt/models.py
+++ b/homeassistant/components/mqtt/models.py
@@ -58,7 +58,7 @@ class PublishMessage:
     retain: bool
 
 
-@dataclass
+@dataclass(slots=True, frozen=True)
 class ReceiveMessage:
     """MQTT Message received."""