Fix N+1 issue on alert group list page (#4738)

# What this PR does

Before:

<img width="267" alt="Screenshot 2024-07-25 at 17 35 28"
src="https://github.com/user-attachments/assets/b0cdcb9d-f658-41cf-9fbb-b61819364dec">

After:
<img width="267" alt="Screenshot 2024-07-25 at 18 11 53"
src="https://github.com/user-attachments/assets/f88c574d-ec9b-4e16-a413-62aa00de6c9a">


## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/apps/alerts/models/alert_group.py

@@ -515,9 +515,15 @@ def slack_app_link(self) -> typing.Optional[str]:
     def telegram_permalink(self) -> typing.Optional[str]:
         from apps.telegram.models.message import TelegramMessage
 
-        main_telegram_message = self.telegram_messages.filter(
-            chat_id__startswith="-", message_type=TelegramMessage.ALERT_GROUP_MESSAGE
-        ).first()
+        try:
+            # prefetched_telegram_messages could be set in apps.api.serializers.alert_group.AlertGroupListSerializer
+            main_telegram_message = self.prefetched_telegram_messages[0] if self.prefetched_telegram_messages else None
+        except AttributeError:
+            main_telegram_message = (
+                self.telegram_messages.filter(chat_id__startswith="-", message_type=TelegramMessage.ALERT_GROUP_MESSAGE)
+                .order_by("id")
+                .first()
+            )
 
         return main_telegram_message.link if main_telegram_message else None
 
@@ -1971,7 +1977,11 @@ def slack_channel_id(self) -> str | None:
 
     @property
     def slack_message(self) -> typing.Optional["SlackMessage"]:
-        return self.slack_messages.order_by("created_at").first()
+        try:
+            # prefetched_slack_messages could be set in apps.api.serializers.alert_group.AlertGroupListSerializer
+            return self.prefetched_slack_messages[0] if self.prefetched_slack_messages else None
+        except AttributeError:
+            return self.slack_messages.order_by("created_at").first()
 
     @cached_property
     def last_stop_escalation_log(self):

engine/apps/api/serializers/alert_group.py

@@ -2,14 +2,18 @@
 import logging
 import typing
 
+from django.conf import settings
 from django.core.cache import cache
+from django.db.models import Prefetch
 from django.utils import timezone
 from drf_spectacular.utils import extend_schema_field
 from rest_framework import serializers
 
 from apps.alerts.incident_appearance.renderers.web_renderer import AlertGroupWebRenderer
 from apps.alerts.models import AlertGroup
 from apps.alerts.models.alert_group import PagedUser
+from apps.slack.models import SlackMessage
+from apps.telegram.models import TelegramMessage
 from common.api_helpers.custom_fields import TeamPrimaryKeyRelatedField
 from common.api_helpers.mixins import EagerLoadingMixin
 
@@ -129,11 +133,26 @@ class AlertGroupListSerializer(
 
     labels = AlertGroupLabelSerializer(many=True, read_only=True)
 
-    PREFETCH_RELATED = [
+    PREFETCH_RELATED: list[str | Prefetch] = [
         "dependent_alert_groups",
         "log_records__author",
         "labels",
     ]
+    if settings.ALERT_GROUP_LIST_TRY_PREFETCH:
+        PREFETCH_RELATED += [
+            Prefetch(
+                "slack_messages",
+                queryset=SlackMessage.objects.select_related("_slack_team_identity").order_by("created_at")[:1],
+                to_attr="prefetched_slack_messages",
+            ),
+            Prefetch(
+                "telegram_messages",
+                queryset=TelegramMessage.objects.filter(
+                    chat_id__startswith="-", message_type=TelegramMessage.ALERT_GROUP_MESSAGE
+                ).order_by("id")[:1],
+                to_attr="prefetched_telegram_messages",
+            ),
+        ]
 
     SELECT_RELATED = [
         "channel__organization",

engine/settings/base.py

@@ -194,6 +194,7 @@ class DatabaseTypes:
 ALERT_GROUPS_DISABLE_PREFER_ORDERING_INDEX = DATABASE_TYPE == DatabaseTypes.MYSQL and getenv_boolean(
     "ALERT_GROUPS_DISABLE_PREFER_ORDERING_INDEX", default=False
 )
+ALERT_GROUP_LIST_TRY_PREFETCH = getenv_boolean("ALERT_GROUP_LIST_TRY_PREFETCH", default=False)
 
 # Redis
 REDIS_USERNAME = os.getenv("REDIS_USERNAME", "")