retention: Add flag to ArchiveTransaction to prevent automatic deletion.

This adds an index non-concurrently, but the table should be small
enough for this to be fine.

zerver/lib/retention.py

@@ -680,12 +680,20 @@ def clean_archived_data() -> None:
     # Associated archived objects will get deleted through the on_delete=CASCADE property:
     count = 0
     transaction_ids = list(
-        ArchiveTransaction.objects.filter(timestamp__lt=check_date).values_list("id", flat=True)
+        ArchiveTransaction.objects.filter(
+            timestamp__lt=check_date, protect_from_deletion=False
+        ).values_list("id", flat=True)
     )
     while len(transaction_ids) > 0:
         transaction_block = transaction_ids[0:TRANSACTION_DELETION_BATCH_SIZE]
         transaction_ids = transaction_ids[TRANSACTION_DELETION_BATCH_SIZE:]
-        ArchiveTransaction.objects.filter(id__in=transaction_block).delete()
+
+        ArchiveTransaction.objects.filter(
+            # The protect_from_deletion=False condition is redundant at this point, but can act
+            # as an extra safeguard against future bugs.
+            id__in=transaction_block,
+            protect_from_deletion=False,
+        ).delete()
         count += len(transaction_block)
 
     logger.info("Deleted %s old ArchiveTransactions.", count)

zerver/migrations/0661_archivetransaction_protect_from_deletion.py

@@ -0,0 +1,17 @@
+# Generated by Django 5.0.10 on 2025-01-28 06:10
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0660_add_imageattachment_content_type"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="archivetransaction",
+            name="protect_from_deletion",
+            field=models.BooleanField(db_index=True, default=False),
+        ),
+    ]

zerver/models/messages.py

@@ -112,6 +112,10 @@ class ArchiveTransaction(models.Model):
     restored = models.BooleanField(default=False, db_index=True)
     restored_timestamp = models.DateTimeField(null=True, db_index=True)
 
+    # ArchiveTransaction objects are regularly deleted. This flag allows tagging
+    # an ArchiveTransaction as protected from such automated deletion.
+    protect_from_deletion = models.BooleanField(default=False, db_index=True)
+
     type = models.PositiveSmallIntegerField(db_index=True)
     # Valid types:
     RETENTION_POLICY_BASED = 1  # Archiving was executed due to automated retention policies

zerver/tests/test_retention.py

@@ -952,24 +952,30 @@ class TestCleaningArchive(ArchiveMessagesTestingBase):
         self._make_expired_zulip_messages(7)
         archive_messages(chunk_size=2)  # Small chunk size to have multiple transactions
 
-        transactions = list(ArchiveTransaction.objects.all())
+        transactions = list(ArchiveTransaction.objects.all().order_by("id"))
         for transaction in transactions[0:-1]:
             transaction.timestamp = timezone_now() - timedelta(
                 days=settings.ARCHIVED_DATA_VACUUMING_DELAY_DAYS + 1
             )
             transaction.save()
 
+        # This transaction would up for deletion, but we enable the flag preventing
+        # it from automatic deletion:
+        transactions[-2].protect_from_deletion = True
+        transactions[-2].save()
+
         message_ids_to_clean = list(
-            ArchivedMessage.objects.filter(archive_transaction__in=transactions[0:-1]).values_list(
+            ArchivedMessage.objects.filter(archive_transaction__in=transactions[0:-2]).values_list(
                 "id", flat=True
             )
         )
 
         clean_archived_data()
-        remaining_transactions = list(ArchiveTransaction.objects.all())
-        self.assert_length(remaining_transactions, 1)
-        # All transactions except the last one were deleted:
+        remaining_transactions = list(ArchiveTransaction.objects.order_by("-id"))
+        self.assert_length(remaining_transactions, 2)
+        # All transactions except the last two were deleted:
         self.assertEqual(remaining_transactions[0].id, transactions[-1].id)
+        self.assertEqual(remaining_transactions[1].id, transactions[-2].id)
         # And corresponding ArchivedMessages should have been deleted:
         self.assertFalse(ArchivedMessage.objects.filter(id__in=message_ids_to_clean).exists())
         self.assertFalse(
@@ -977,7 +983,10 @@ class TestCleaningArchive(ArchiveMessagesTestingBase):
         )
 
         for message in ArchivedMessage.objects.all():
-            self.assertEqual(message.archive_transaction_id, remaining_transactions[0].id)
+            self.assertIn(
+                message.archive_transaction_id,
+                [remaining_transactions[0].id, remaining_transactions[1].id],
+            )
 
 
 class TestGetRealmAndStreamsForArchiving(ZulipTestCase):