user_topics: Handle IntegrityError during bulk insertion.

When there was a race during bulk insertion of UserTopic
rows, it resulted in Integrity error.

We update the 'last_updated' and 'visibility_policy'
columns for conflicting rows.

We also removed the separate update query to update
visibility_policy because now the new SQL query can
handle the updates too. This leads to have fewer round
trips to the database.

zerver/lib/user_topics.py

@@ -3,9 +3,10 @@ from collections import defaultdict
 from datetime import datetime
 from typing import Callable, Dict, List, Optional, Tuple, TypedDict
 
-from django.db import transaction
+from django.db import connection, transaction
 from django.db.models import QuerySet
 from django.utils.timezone import now as timezone_now
+from psycopg2.sql import SQL, Literal
 from sqlalchemy.sql import ClauseElement, and_, column, not_, or_
 from sqlalchemy.types import Integer
 
@@ -162,7 +163,9 @@ def bulk_set_user_topic_visibility_policy_in_database(
     assert last_updated is not None
     assert recipient_id is not None
 
-    user_profiles_seeking_visibility_policy_update: List[UserProfile] = []
+    user_profiles_seeking_user_topic_update_or_create: List[UserProfile] = (
+        user_profiles_without_visibility_policy
+    )
     for row in rows:
         if row.visibility_policy == visibility_policy:
             logging.info(
@@ -172,26 +175,39 @@ def bulk_set_user_topic_visibility_policy_in_database(
             )
             continue
         # The request is to just 'update' the visibility policy of a topic
-        user_profiles_seeking_visibility_policy_update.append(row.user_profile)
+        user_profiles_seeking_user_topic_update_or_create.append(row.user_profile)
 
-    if user_profiles_seeking_visibility_policy_update:
-        rows.filter(user_profile__in=user_profiles_seeking_visibility_policy_update).update(
-            visibility_policy=visibility_policy, last_updated=last_updated
-        )
-
-    if user_profiles_without_visibility_policy:
-        UserTopic.objects.bulk_create(
-            UserTopic(
-                user_profile=user_profile,
-                stream_id=stream_id,
-                recipient_id=recipient_id,
-                topic_name=topic_name,
-                last_updated=last_updated,
-                visibility_policy=visibility_policy,
+    if user_profiles_seeking_user_topic_update_or_create:
+        user_profile_ids_array = SQL("ARRAY[{}]").format(
+            SQL(", ").join(
+                [
+                    Literal(user_profile.id)
+                    for user_profile in user_profiles_seeking_user_topic_update_or_create
+                ]
             )
-            for user_profile in user_profiles_without_visibility_policy
         )
-    return user_profiles_seeking_visibility_policy_update + user_profiles_without_visibility_policy
+
+        query = SQL("""
+            INSERT INTO zerver_usertopic(user_profile_id, stream_id, recipient_id, topic_name, last_updated, visibility_policy)
+            SELECT * FROM UNNEST({user_profile_ids_array}) AS user_profile(user_profile_id)
+            CROSS JOIN (VALUES ({stream_id}, {recipient_id}, {topic_name}, {last_updated}, {visibility_policy}))
+            AS other_values(stream_id, recipient_id, topic_name, last_updated, visibility_policy)
+            ON CONFLICT (user_profile_id, stream_id, lower(topic_name)) DO UPDATE SET
+            last_updated = EXCLUDED.last_updated,
+            visibility_policy = EXCLUDED.visibility_policy;
+        """).format(
+            user_profile_ids_array=user_profile_ids_array,
+            stream_id=Literal(stream_id),
+            recipient_id=Literal(recipient_id),
+            topic_name=Literal(topic_name),
+            last_updated=Literal(last_updated),
+            visibility_policy=Literal(visibility_policy),
+        )
+
+        with connection.cursor() as cursor:
+            cursor.execute(query)
+
+    return user_profiles_seeking_user_topic_update_or_create
 
 
 def topic_has_visibility_policy(