diff --git a/zerver/lib/test_classes.py b/zerver/lib/test_classes.py
index e19d23bf43..bdc38f2d0f 100644
--- a/zerver/lib/test_classes.py
+++ b/zerver/lib/test_classes.py
@@ -141,6 +141,10 @@ class UploadSerializeMixin(SerializeMixin):
 class ZulipTestCaseMixin(SimpleTestCase):
     # Ensure that the test system just shows us diffs
     maxDiff: Optional[int] = None
+    # This bypasses BAN_CONSOLE_OUTPUT for the test case when set.
+    # Override this to verify if the given extra console output matches the
+    # expectation.
+    expected_console_output: Optional[str] = None
 
     def setUp(self) -> None:
         super().setUp()
@@ -170,7 +174,7 @@ class ZulipTestCaseMixin(SimpleTestCase):
             self.mock_initialize.stop()
 
     def run(self, result: Optional[TestResult] = None) -> Optional[TestResult]:  # nocoverage
-        if not settings.BAN_CONSOLE_OUTPUT:
+        if not settings.BAN_CONSOLE_OUTPUT and self.expected_console_output is None:
             return super().run(result)
         extra_output_finder = ExtraConsoleOutputFinder()
         with tee_stderr_and_find_extra_console_output(
@@ -180,6 +184,11 @@ class ZulipTestCaseMixin(SimpleTestCase):
         if extra_output_finder.full_extra_output and (
             test_result is None or test_result.wasSuccessful()
         ):
+            extra_output = extra_output_finder.full_extra_output.decode(errors="replace")
+            if self.expected_console_output is not None:
+                self.assertEqual(extra_output, self.expected_console_output)
+                return test_result
+
             exception_message = f"""
 ---- UNEXPECTED CONSOLE OUTPUT DETECTED ----
 
@@ -196,7 +205,7 @@ You should be able to quickly reproduce this failure with:
 ./tools/test-backend --ban-console-output {self.id()}
 
 Output:
-{extra_output_finder.full_extra_output.decode(errors="replace")}
+{extra_output}
 --------------------------------------------
 """
             raise ExtraConsoleOutputInTestError(exception_message)
diff --git a/zerver/migrations/0460_backfill_realmauditlog_extradata_to_json_field.py b/zerver/migrations/0460_backfill_realmauditlog_extradata_to_json_field.py
new file mode 100644
index 0000000000..8bcc35c0d1
--- /dev/null
+++ b/zerver/migrations/0460_backfill_realmauditlog_extradata_to_json_field.py
@@ -0,0 +1,181 @@
+# Generated by Django 4.0.7 on 2022-09-30 20:30
+
+import ast
+from typing import List, Tuple, Type
+
+import orjson
+from django.db import migrations, transaction
+from django.db.backends.base.schema import BaseDatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+from django.db.models import F, JSONField, Model
+from django.db.models.functions import Cast, JSONObject
+
+# This migration is mostly the same as
+# backfill_remote_realmauditlog_extradata_to_json_field in zilencer.
+
+OLD_VALUE = "1"
+NEW_VALUE = "2"
+USER_FULL_NAME_CHANGED = 124
+REALM_DISCOUNT_CHANGED = 209
+BATCH_SIZE = 5000
+
+DISCOUNT_DATA_TEMPLATE = """Audit log entry {id} with event type REALM_DISCOUNT_CHANGED is skipped.
+The data consistency needs to be manually checked.
+  Discount data to remove after the upcoming JSONField migration:
+{data_to_remove}
+  Discount data to keep after the upcoming JSONField migration:
+{data_to_keep}
+"""
+
+OVERWRITE_TEMPLATE = """Audit log entry with id {id} has extra_data_json been inconsistently overwritten.
+  The old value is:
+{old_value}
+  The new value is:
+{new_value}
+"""
+
+
+@transaction.atomic
+def do_bulk_backfill_extra_data(
+    audit_log_model: Type[Model], id_lower_bound: int, id_upper_bound: int
+) -> None:
+    # First handle the special case for audit logs with the
+    # USER_FULL_NAME_CHANGED event, which stores the full name not as
+    # str(dict()) but a plain str. Note that we only update the entries where
+    # extra_data_json has the default value, because we do not want to override
+    # existing audit log entries with a NEW_VALUE of None for extra_data_json.
+    # We do not need to skip existing entries for other parts of backfilling
+    # because we have double-write implemented so that the backfilled value
+    # will still be consistent.
+    audit_log_model.objects.filter(
+        event_type=USER_FULL_NAME_CHANGED,
+        id__range=(id_lower_bound, id_upper_bound),
+        extra_data_json={},
+        # extra_data used to keeps track of the old name. As a result, we know
+        # nothing about what NEW_VALUE would be especially if the name has been
+        # changed multiple times. extra_data_json is a JSONObject whose
+        # OLD_VALUE and NEW_VALUE is mapped from the value of the extra_data
+        # field (which is just a old full name string) and None, respectively.
+        # Documentation for JSONObject:
+        # https://docs.djangoproject.com/en/4.2/ref/models/database-functions/#jsonobject
+    ).update(extra_data_json=JSONObject(**{OLD_VALUE: "extra_data", NEW_VALUE: None}))
+
+    inconsistent_extra_data_json: List[Tuple[int, str, object, object]] = []
+    # A dict converted with str() will start with a open bracket followed by a
+    # single quote, as opposed to a JSON-encoded value, which will use a
+    # _double_ quote. We use this to filter out those entries with malformed
+    # extra_data to be handled later. This should only update rows with
+    # extra_data populated with orjson.dumps.
+
+    # The first query below checks for entries that would have extra_data_json
+    # being overwritten by the migration with a value inconsistent with its
+    # previous value.
+    inconsistent_extra_data_json.extend(
+        audit_log_model.objects.filter(
+            extra_data__isnull=False, id__range=(id_lower_bound, id_upper_bound)
+        )
+        .annotate(new_extra_data_json=Cast("extra_data", output_field=JSONField()))
+        .exclude(extra_data__startswith="{'")
+        .exclude(event_type=USER_FULL_NAME_CHANGED)
+        .exclude(extra_data_json={})
+        .exclude(extra_data_json=F("new_extra_data_json"))
+        .values_list("id", "extra_data", "extra_data_json", "new_extra_data_json")
+    )
+    (
+        audit_log_model.objects.filter(
+            extra_data__isnull=False,
+            id__range=(id_lower_bound, id_upper_bound),
+            extra_data_json__inconsistent_old_extra_data__isnull=True,
+        )
+        .exclude(extra_data__startswith="{'")
+        .exclude(event_type=USER_FULL_NAME_CHANGED)
+        .update(extra_data_json=Cast("extra_data", output_field=JSONField()))
+    )
+
+    python_valued_audit_log_entries = audit_log_model.objects.filter(
+        extra_data__startswith="{'",
+        id__range=(id_lower_bound, id_upper_bound),
+        extra_data_json__inconsistent_old_extra_data__isnull=True,
+    )
+    for audit_log_entry in python_valued_audit_log_entries:
+        # extra_data for entries that store dict stringified with builtins.str()
+        # are converted back with ast.literal_eval for safety and efficiency.
+        # str()'d extra_data with the REALM_DISCOUNT_CHANGED event type is not
+        # handled by this migration. We expect that all such entries are
+        # manually converted beforehand or an error will occur during the
+        # migration, because ast.literal_eval does not allow the evaluation of
+        # Decimal.
+        old_value = audit_log_entry.extra_data_json  # type: ignore[attr-defined] # The migration cannot depend on zerver.models, which contains the real type of the RealmAuditLog model, so it cannot be properly typed.
+        if audit_log_entry.event_type == REALM_DISCOUNT_CHANGED:  # type: ignore[attr-defined] # Explained above.
+            print(
+                DISCOUNT_DATA_TEMPLATE.format(
+                    id=audit_log_entry.id,  # type: ignore[attr-defined] # Explained above.
+                    data_to_remove=audit_log_entry.extra_data,  # type: ignore[attr-defined] # Explained above.
+                    data_to_keep=old_value,
+                )
+            )
+            continue
+        new_value = ast.literal_eval(audit_log_entry.extra_data)  # type: ignore[attr-defined] # Explained above.
+        if old_value != {} and old_value != new_value:
+            inconsistent_extra_data_json.append((audit_log_entry.id, audit_log_entry.extra_data, old_value, new_value))  # type: ignore[attr-defined] # Explained above.
+        audit_log_entry.extra_data_json = new_value  # type: ignore[attr-defined] # Explained above.
+    audit_log_model.objects.bulk_update(python_valued_audit_log_entries, fields=["extra_data_json"])
+
+    if inconsistent_extra_data_json:
+        audit_log_entries = []
+        for (
+            audit_log_entry_id,
+            old_extra_data,
+            old_extra_data_json,
+            new_extra_data_json,
+        ) in inconsistent_extra_data_json:
+            audit_log_entry = audit_log_model.objects.get(id=audit_log_entry_id)
+            assert isinstance(old_extra_data_json, dict)
+            if "inconsistent_old_extra_data" in old_extra_data_json:
+                # Skip entries that have been backfilled and detected as
+                # anomalies before.
+                continue
+            assert isinstance(new_extra_data_json, dict)
+            audit_log_entry.extra_data_json = {  # type: ignore[attr-defined] # Explained above.
+                **new_extra_data_json,
+                "inconsistent_old_extra_data": old_extra_data,
+                "inconsistent_old_extra_data_json": old_extra_data_json,
+            }
+            audit_log_entries.append(audit_log_entry)
+            print(
+                OVERWRITE_TEMPLATE.format(
+                    id=audit_log_entry_id,
+                    old_value=orjson.dumps(old_extra_data_json).decode(),
+                    new_value=orjson.dumps(new_extra_data_json).decode(),
+                )
+            )
+        audit_log_model.objects.bulk_update(audit_log_entries, fields=["extra_data_json"])
+
+
+def backfill_extra_data(apps: StateApps, schema_editor: BaseDatabaseSchemaEditor) -> None:
+    audit_log_model = apps.get_model("zerver", "RealmAuditLog")
+    if not audit_log_model.objects.filter(extra_data__isnull=False).exists():
+        return
+
+    audit_log_entries = audit_log_model.objects.filter(extra_data__isnull=False)
+    id_lower_bound = audit_log_entries.earliest("id").id
+    id_upper_bound = audit_log_entries.latest("id").id
+    while id_lower_bound <= id_upper_bound:
+        do_bulk_backfill_extra_data(
+            audit_log_model, id_lower_bound, min(id_lower_bound + BATCH_SIZE, id_upper_bound)
+        )
+        id_lower_bound += BATCH_SIZE + 1
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zerver", "0459_remove_invalid_characters_from_user_group_name"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            backfill_extra_data, reverse_code=migrations.RunPython.noop, elidable=True
+        ),
+    ]
diff --git a/zerver/tests/test_migrations.py b/zerver/tests/test_migrations.py
index bab4c46fe0..dfaece8824 100644
--- a/zerver/tests/test_migrations.py
+++ b/zerver/tests/test_migrations.py
@@ -4,8 +4,12 @@
 # You can also read
 #   https://www.caktusgroup.com/blog/2016/02/02/writing-unit-tests-django-migrations/
 # to get a tutorial on the framework that inspired this feature.
+from decimal import Decimal
+from typing import Optional
 
+import orjson
 from django.db.migrations.state import StateApps
+from django.utils.timezone import now as timezone_now
 
 from zerver.lib.test_classes import MigrationsTestCase
 from zerver.lib.test_helpers import use_db_models
@@ -25,89 +29,239 @@ from zerver.lib.test_helpers import use_db_models
 # As a result, we generally mark these tests as skipped once they have
 # been tested for a migration being merged.
 
+USER_ACTIVATED = 102
+USER_FULL_NAME_CHANGED = 124
+REALM_DISCOUNT_CHANGED = 209
+OLD_VALUE = "1"
+NEW_VALUE = "2"
 
-class LinkifierURLFormatString(MigrationsTestCase):
-    migrate_from = "0440_realmfilter_url_template"
-    migrate_to = "0441_backfill_realmfilter_url_template"
+
+class RealmAuditLogExtraData(MigrationsTestCase):
+    migrate_from = "0459_remove_invalid_characters_from_user_group_name"
+    migrate_to = "0460_backfill_realmauditlog_extradata_to_json_field"
+
+    full_name_change_log_id: Optional[int] = None
+    valid_json_log_id: Optional[int] = None
+    str_json_log_id: Optional[int] = None
+    # The BATCH_SIZE is defined as 5000 in
+    # backfill_realmauditlog_extradata_to_json_field, this later is used to test
+    # if batching works properly.
+    DATA_SIZE = 10005
+    expected_console_output = """Audit log entry 50003 with event type REALM_DISCOUNT_CHANGED is skipped.
+The data consistency needs to be manually checked.
+  Discount data to remove after the upcoming JSONField migration:
+{'old_discount': Decimal('25.0000'), 'new_discount': Decimal('50')}
+  Discount data to keep after the upcoming JSONField migration:
+{}
+
+Audit log entry 50004 with event type REALM_DISCOUNT_CHANGED is skipped.
+The data consistency needs to be manually checked.
+  Discount data to remove after the upcoming JSONField migration:
+{'old_discount': Decimal('25.0000'), 'new_discount': Decimal('50')}
+  Discount data to keep after the upcoming JSONField migration:
+{'new_discount': '50', 'old_discount': '25.0000'}
+
+Audit log entry with id 50001 has extra_data_json been inconsistently overwritten.
+  The old value is:
+{"corrupted":"foo"}
+  The new value is:
+{"key":"value"}
+
+Audit log entry with id 50002 has extra_data_json been inconsistently overwritten.
+  The old value is:
+{"corrupted":"bar"}
+  The new value is:
+{"key":"value"}
+
+"""
 
     @use_db_models
     def setUpBeforeMigration(self, apps: StateApps) -> None:
-        RealmFilter = apps.get_model("zerver", "RealmFilter")
+        Realm = apps.get_model("zerver", "Realm")
+        RealmAuditLog = apps.get_model("zerver", "RealmAuditLog")
+        event_time = timezone_now()
+        realm = Realm.objects.get(string_id="zulip")
 
-        iago = self.example_user("iago")
+        full_name_change_log = RealmAuditLog(
+            realm=realm,
+            event_type=USER_FULL_NAME_CHANGED,
+            event_time=event_time,
+            extra_data="foo",
+        )
 
-        urls = [
-            "http://example.com/",
-            "https://example.com/",
-            "https://user:password@example.com/",
-            "https://example.com/@user/thing",
-            "https://example.com/!path",
-            "https://example.com/foo.bar",
-            "https://example.com/foo[bar]",
-            "https://example.com/{foo}",
-            "https://example.com/{foo}{bars}",
-            "https://example.com/{foo}/and/{bar}",
-            "https://example.com/?foo={foo}",
-            "https://example.com/%ab",
-            "https://example.com/%ba",
-            "https://example.com/%21",
-            "https://example.com/words%20with%20spaces",
-            "https://example.com/back%20to%20{back}",
-            "https://example.com/encoded%2fwith%2fletters",
-            "https://example.com/encoded%2Fwith%2Fupper%2Fcase%2Fletters",
-            "https://example.com/%%",
-            "https://example.com/%%(",
-            "https://example.com/%%()",
-            "https://example.com/%%(foo",
-            "https://example.com/%%(foo)",
-            "https://example.com/%%(foo)s",
-            "https://example.com/%(foo)s",
-            "https://example.com/%(foo)s%(bar)s",
-        ]
-        self.linkifier_ids = []
+        new_full_name_change_log = RealmAuditLog(
+            realm=realm,
+            event_type=USER_FULL_NAME_CHANGED,
+            event_time=event_time,
+            extra_data="foo",
+            extra_data_json={OLD_VALUE: "foo", NEW_VALUE: "bar"},
+        )
 
-        for index, url in enumerate(urls):
-            self.linkifier_ids.append(
-                RealmFilter.objects.create(
-                    realm=iago.realm,
-                    pattern=f"dummy{index}",
-                    url_format_string=url,
-                ).id
+        valid_json_log = RealmAuditLog(
+            realm=realm,
+            event_type=USER_ACTIVATED,
+            event_time=event_time,
+            extra_data=orjson.dumps({"key": "value"}).decode(),
+        )
+
+        str_json_log = RealmAuditLog(
+            realm=realm,
+            event_type=USER_ACTIVATED,
+            event_time=event_time,
+            extra_data=str({"key": "value"}),
+        )
+
+        self.backfilled_inconsistent_log_id = RealmAuditLog.objects.create(
+            realm=realm,
+            event_type=USER_ACTIVATED,
+            event_time=event_time,
+            extra_data=orjson.dumps({"key": "baz"}).decode(),
+            extra_data_json={
+                "key": "baz",
+                "inconsistent_old_extra_data": orjson.dumps({"key": "baz"}).decode(),
+                "inconsistent_old_extra_data_json": {"key": "value corrupted"},
+            },
+        ).id
+
+        # The following audit log entries have preset ids because we use
+        # them to assert the generated log output that is defined before
+        # the test case is run.
+        inconsistent_json_log = RealmAuditLog(
+            id=50001,
+            realm=realm,
+            event_type=USER_ACTIVATED,
+            event_time=event_time,
+            extra_data=orjson.dumps({"key": "value"}).decode(),
+            extra_data_json={"corrupted": "foo"},
+        )
+
+        inconsistent_str_json_log = RealmAuditLog(
+            id=50002,
+            realm=realm,
+            event_type=USER_ACTIVATED,
+            event_time=event_time,
+            extra_data=str({"key": "value"}),
+            extra_data_json={"corrupted": "bar"},
+        )
+
+        self.old_decimal_log_id = RealmAuditLog.objects.create(
+            id=50003,
+            realm=realm,
+            event_type=REALM_DISCOUNT_CHANGED,
+            event_time=event_time,
+            extra_data=str({"old_discount": Decimal("25.0000"), "new_discount": Decimal("50")}),
+        ).id
+
+        self.new_decimal_log_id = RealmAuditLog.objects.create(
+            id=50004,
+            realm=realm,
+            event_type=REALM_DISCOUNT_CHANGED,
+            event_time=event_time,
+            extra_data=str({"old_discount": Decimal("25.0000"), "new_discount": Decimal("50")}),
+            extra_data_json={"old_discount": Decimal("25.0000"), "new_discount": Decimal("50")},
+        ).id
+
+        RealmAuditLog.objects.bulk_create(
+            [
+                full_name_change_log,
+                new_full_name_change_log,
+                valid_json_log,
+                str_json_log,
+                inconsistent_json_log,
+                inconsistent_str_json_log,
+            ]
+        )
+        self.full_name_change_log_id = full_name_change_log.id
+        self.new_full_name_change_log_id = new_full_name_change_log.id
+        self.valid_json_log_id = valid_json_log.id
+        self.str_json_log_id = str_json_log.id
+
+        other_logs = []
+        for i in range(self.DATA_SIZE):
+            other_logs.append(
+                RealmAuditLog(
+                    realm=realm,
+                    event_type=USER_ACTIVATED,
+                    event_time=event_time,
+                    extra_data=orjson.dumps({"data": i}).decode(),
+                )
             )
-
-    def test_converted_url_templates(self) -> None:
-        RealmFilter = self.apps.get_model("zerver", "RealmFilter")
-
-        expected_urls = [
-            "http://example.com/",
-            "https://example.com/",
-            "https://user:password@example.com/",
-            "https://example.com/@user/thing",
-            "https://example.com/!path",
-            "https://example.com/foo.bar",
-            "https://example.com/foo[bar]",
-            "https://example.com/%7Bfoo%7D",
-            "https://example.com/%7Bfoo%7D%7Bbars%7D",
-            "https://example.com/%7Bfoo%7D/and/%7Bbar%7D",
-            "https://example.com/?foo=%7Bfoo%7D",
-            "https://example.com/%ab",
-            "https://example.com/%ba",
-            "https://example.com/%21",
-            "https://example.com/words%20with%20spaces",
-            "https://example.com/back%20to%20%7Bback%7D",
-            "https://example.com/encoded%2fwith%2fletters",
-            "https://example.com/encoded%2Fwith%2Fupper%2Fcase%2Fletters",
-            "https://example.com/%",
-            "https://example.com/%(",
-            "https://example.com/%()",
-            "https://example.com/%(foo",
-            "https://example.com/%(foo)",
-            "https://example.com/%(foo)s",
-            "https://example.com/{foo}",
-            "https://example.com/{foo}{bar}",
+        self.other_logs_id = [
+            audit_log.id for audit_log in RealmAuditLog.objects.bulk_create(other_logs)
         ]
 
-        for linkifier_id, expected in zip(self.linkifier_ids, expected_urls):
-            linkifier = RealmFilter.objects.filter(id=linkifier_id).first()
-            self.assertIsNotNone(linkifier)
-            self.assertEqual(linkifier.url_template, expected)
+        # No new audit log entry should have extra_data_json populated as of
+        # now except for the entries created with non-default values.
+        self.assert_length(
+            RealmAuditLog.objects.filter(
+                event_time__gte=event_time,
+            ).exclude(
+                extra_data_json={},
+            ),
+            5,
+        )
+
+    def test_realmaudit_log_extra_data_to_json(self) -> None:
+        RealmAuditLog = self.apps.get_model("zerver", "RealmAuditLog")
+
+        self.assertIsNotNone(self.full_name_change_log_id)
+        self.assertIsNotNone(self.valid_json_log_id)
+        self.assertIsNotNone(self.str_json_log_id)
+
+        full_name_change_log = RealmAuditLog.objects.filter(id=self.full_name_change_log_id).first()
+        new_full_name_change_log = RealmAuditLog.objects.filter(
+            id=self.new_full_name_change_log_id
+        ).first()
+        valid_json_log = RealmAuditLog.objects.filter(id=self.valid_json_log_id).first()
+        str_json_log = RealmAuditLog.objects.filter(id=self.str_json_log_id).first()
+
+        self.assertIsNotNone(full_name_change_log)
+        self.assertEqual(full_name_change_log.extra_data_json, {"1": "foo", "2": None})
+
+        self.assertIsNotNone(new_full_name_change_log)
+        self.assertEqual(new_full_name_change_log.extra_data_json, {"1": "foo", "2": "bar"})
+
+        self.assertIsNotNone(valid_json_log)
+        self.assertEqual(valid_json_log.extra_data_json, {"key": "value"})
+
+        self.assertIsNotNone(str_json_log)
+        self.assertEqual(str_json_log.extra_data_json, {"key": "value"})
+
+        other_logs = RealmAuditLog.objects.filter(id__in=self.other_logs_id).order_by("id")
+        self.assertIsNotNone(other_logs)
+        self.assert_length(other_logs, self.DATA_SIZE)
+        for index, audit_log in enumerate(other_logs):
+            self.assertEqual(audit_log.extra_data_json, {"data": index})
+
+        inconsistent_json_log = RealmAuditLog.objects.get(
+            extra_data_json__inconsistent_old_extra_data=orjson.dumps({"key": "value"}).decode()
+        )
+        self.assertIsNotNone(inconsistent_json_log)
+        self.assertEqual(inconsistent_json_log.id, 50001)
+        self.assertEqual(
+            inconsistent_json_log.extra_data_json["inconsistent_old_extra_data_json"],
+            {"corrupted": "foo"},
+        )
+
+        inconsistent_str_json_log = RealmAuditLog.objects.get(
+            extra_data_json__inconsistent_old_extra_data=str({"key": "value"})
+        )
+        self.assertIsNotNone(inconsistent_str_json_log)
+        self.assertEqual(inconsistent_str_json_log.id, 50002)
+        self.assertEqual(
+            inconsistent_str_json_log.extra_data_json["inconsistent_old_extra_data_json"],
+            {"corrupted": "bar"},
+        )
+
+        backfilled_inconsistent_log = RealmAuditLog.objects.get(
+            id=self.backfilled_inconsistent_log_id
+        )
+        self.assertIsNotNone(backfilled_inconsistent_log)
+        self.assertEqual(
+            backfilled_inconsistent_log.extra_data_json,
+            {
+                "key": "baz",
+                "inconsistent_old_extra_data": orjson.dumps({"key": "baz"}).decode(),
+                "inconsistent_old_extra_data_json": {"key": "value corrupted"},
+            },
+        )
diff --git a/zilencer/migrations/0027_backfill_remote_realmauditlog_extradata_to_json_field.py b/zilencer/migrations/0027_backfill_remote_realmauditlog_extradata_to_json_field.py
new file mode 100644
index 0000000000..71e449e381
--- /dev/null
+++ b/zilencer/migrations/0027_backfill_remote_realmauditlog_extradata_to_json_field.py
@@ -0,0 +1,148 @@
+# Generated by Django 4.0.7 on 2022-09-30 20:30
+
+import ast
+from typing import Callable, List, Tuple, Type
+
+import orjson
+from django.db import migrations, transaction
+from django.db.backends.base.schema import BaseDatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+from django.db.models import F, JSONField, Model
+from django.db.models.functions import Cast
+
+# This migration is mostly the same as
+# backfill_realmauditlog_extradata_to_json_field in zerver.
+
+OLD_VALUE = "1"
+NEW_VALUE = "2"
+USER_FULL_NAME_CHANGED = 124
+REALM_DISCOUNT_CHANGED = 209
+BATCH_SIZE = 5000
+
+OVERWRITE_TEMPLATE = """Audit log entry with id {id} has extra_data_json been inconsistently overwritten.
+  The old value is:
+{old_value}
+  The new value is:
+{new_value}
+"""
+
+
+@transaction.atomic
+def do_bulk_backfill_extra_data(
+    audit_log_model: Type[Model], id_lower_bound: int, id_upper_bound: int
+) -> None:
+    inconsistent_extra_data_json: List[Tuple[int, str, object, object]] = []
+    # A dict converted with str() will start with a open bracket followed by a
+    # single quote, as opposed to a JSON-encoded value, which will use a
+    # _double_ quote. We use this to filter out those entries with malformed
+    # extra_data to be handled later. This should only update rows with
+    # extra_data populated with orjson.dumps.
+
+    # The first query below checks for entries that would have extra_data_json
+    # being overwritten by the migration with a value inconsistent with its
+    # previous value.
+    inconsistent_extra_data_json.extend(
+        audit_log_model.objects.filter(
+            extra_data__isnull=False, id__range=(id_lower_bound, id_upper_bound)
+        )
+        .annotate(new_extra_data_json=Cast("extra_data", output_field=JSONField()))
+        .exclude(extra_data__startswith="{'")
+        .exclude(extra_data_json={})
+        .exclude(extra_data_json=F("new_extra_data_json"))
+        .values_list("id", "extra_data", "extra_data_json", "new_extra_data_json")
+    )
+    (
+        audit_log_model.objects.filter(
+            extra_data__isnull=False,
+            id__range=(id_lower_bound, id_upper_bound),
+            extra_data_json__inconsistent_old_extra_data__isnull=True,
+        )
+        .exclude(extra_data__startswith="{'")
+        .update(extra_data_json=Cast("extra_data", output_field=JSONField()))
+    )
+
+    python_valued_audit_log_entries = audit_log_model.objects.filter(
+        extra_data__startswith="{'",
+        id__range=(id_lower_bound, id_upper_bound),
+        extra_data_json__inconsistent_old_extra_data__isnull=True,
+    )
+    for audit_log_entry in python_valued_audit_log_entries:
+        # extra_data for entries that store dict stringified with builtins.str()
+        # are converted back with ast.literal_eval for safety and efficiency.
+        old_value = audit_log_entry.extra_data_json  # type: ignore[attr-defined] # The migration cannot depend on zerver.models, which contains the real type of the RealmAuditLog model, so it cannot be properly typed.
+        new_value = ast.literal_eval(audit_log_entry.extra_data)  # type: ignore[attr-defined] # Explained above.
+        if old_value != {} and old_value != new_value:
+            inconsistent_extra_data_json.append((audit_log_entry.id, audit_log_entry.extra_data, old_value, new_value))  # type: ignore[attr-defined] # Explained above.
+        audit_log_entry.extra_data_json = new_value  # type: ignore[attr-defined] # Explained above.
+    audit_log_model.objects.bulk_update(python_valued_audit_log_entries, fields=["extra_data_json"])
+
+    if inconsistent_extra_data_json:
+        audit_log_entries = []
+        for (
+            audit_log_entry_id,
+            old_extra_data,
+            old_extra_data_json,
+            new_extra_data_json,
+        ) in inconsistent_extra_data_json:
+            audit_log_entry = audit_log_model.objects.get(id=audit_log_entry_id)
+            assert isinstance(old_extra_data_json, dict)
+            if "inconsistent_old_extra_data" in old_extra_data_json:
+                # Skip entries that have been backfilled and detected as
+                # anomalies before.
+                continue
+            assert isinstance(new_extra_data_json, dict)
+            audit_log_entry.extra_data_json = {  # type: ignore[attr-defined] # Explained above.
+                **new_extra_data_json,
+                "inconsistent_old_extra_data": old_extra_data,
+                "inconsistent_old_extra_data_json": old_extra_data_json,
+            }
+            audit_log_entries.append(audit_log_entry)
+            print(
+                OVERWRITE_TEMPLATE.format(
+                    id=audit_log_entry_id,
+                    old_value=orjson.dumps(old_extra_data_json).decode(),
+                    new_value=orjson.dumps(new_extra_data_json).decode(),
+                )
+            )
+        audit_log_model.objects.bulk_update(audit_log_entries, fields=["extra_data_json"])
+
+
+def backfill_extra_data(model_name: str) -> Callable[[StateApps, BaseDatabaseSchemaEditor], None]:
+    def inner(apps: StateApps, schema_editor: BaseDatabaseSchemaEditor) -> None:
+        audit_log_model = apps.get_model("zilencer", model_name)
+        if not audit_log_model.objects.filter(extra_data__isnull=False).exists():
+            return
+
+        audit_log_entries = audit_log_model.objects.filter(extra_data__isnull=False)
+        id_lower_bound = audit_log_entries.earliest("id").id
+        id_upper_bound = audit_log_entries.latest("id").id
+        while id_lower_bound <= id_upper_bound:
+            do_bulk_backfill_extra_data(
+                audit_log_model, id_lower_bound, min(id_lower_bound + BATCH_SIZE, id_upper_bound)
+            )
+            id_lower_bound += BATCH_SIZE + 1
+
+        do_bulk_backfill_extra_data(audit_log_model, id_lower_bound, id_upper_bound)
+
+    return inner
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zilencer", "0026_auditlog_models_extra_data_json"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            backfill_extra_data("RemoteRealmAuditLog"),
+            reverse_code=migrations.RunPython.noop,
+            elidable=True,
+        ),
+        migrations.RunPython(
+            backfill_extra_data("RemoteZulipServerAuditLog"),
+            reverse_code=migrations.RunPython.noop,
+            elidable=True,
+        ),
+    ]