models: Add (realm, create_time) index for the Attachment table.

zerver/migrations/0520_attachment_zerver_attachment_realm_create_time.py

@@ -0,0 +1,23 @@
+# Generated by Django 5.0.6 on 2024-05-08 01:16
+
+from django.contrib.postgres.operations import AddIndexConcurrently
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zerver", "0519_archivetransaction_restored_timestamp"),
+    ]
+
+    operations = [
+        AddIndexConcurrently(
+            model_name="attachment",
+            index=models.Index(
+                models.F("realm"),
+                models.F("create_time"),
+                name="zerver_attachment_realm_create_time",
+            ),
+        ),
+    ]

zerver/models/messages.py

@@ -713,6 +713,15 @@ class Attachment(AbstractAttachment):
     # because ScheduledMessage is not subject to archiving.
     scheduled_messages = models.ManyToManyField("zerver.ScheduledMessage")
 
+    class Meta:
+        indexes = [
+            models.Index(
+                "realm",
+                "create_time",
+                name="zerver_attachment_realm_create_time",
+            ),
+        ]
+
     def is_claimed(self) -> bool:
         return self.messages.exists() or self.scheduled_messages.exists()