feast-dev · ntkathole · Jun 9, 2026 · Jun 8, 2026 · Jun 8, 2026 · Jun 9, 2026
@@ -236,18 +236,45 @@ def _table_tags(online_config, table_instance) -> list[dict[str, str]]:
 
     @staticmethod
     def _update_tags(dynamodb_client, table_name: str, new_tags: list[dict[str, str]]):
+        """Update DynamoDB table tags using a diff-based approach.
+
+        Instead of removing all tags and re-adding them (which is vulnerable to
+        the eventual-consistency window between UntagResource and TagResource),
+        this method computes the minimal set of changes needed:
+
+        - Only removes tags that are no longer present in new_tags.
+        - Only adds/updates tags whose value has changed or that are new.
+
+        This avoids the race condition described in
+        https://github.com/feast-dev/feast/issues/6418 where calling
+        TagResource immediately after UntagResource can leave a table with no
+        tags due to DynamoDB's asynchronous tag operations.
+        """
         table_arn = dynamodb_client.describe_table(TableName=table_name)["Table"][
             "TableArn"
         ]
         current_tags = dynamodb_client.list_tags_of_resource(ResourceArn=table_arn)[
             "Tags"
         ]
-        if current_tags:
-            remove_keys = [tag["Key"] for tag in current_tags]
-            dynamodb_client.untag_resource(ResourceArn=table_arn, TagKeys=remove_keys)
 
-        if new_tags:
-            dynamodb_client.tag_resource(ResourceArn=table_arn, Tags=new_tags)
+        current_tag_map = {tag["Key"]: tag["Value"] for tag in current_tags}
+        new_tag_map = {tag["Key"]: tag["Value"] for tag in new_tags}
+
+        # Remove only tags that are no longer in new_tags
+        keys_to_remove = [k for k in current_tag_map if k not in new_tag_map]
+        # Add / update only tags whose value is new or has changed
+        tags_to_add = [
+            {"Key": k, "Value": v}
+            for k, v in new_tag_map.items()
+            if current_tag_map.get(k) != v
+        ]
+
+        if keys_to_remove:
+            dynamodb_client.untag_resource(
+                ResourceArn=table_arn, TagKeys=keys_to_remove
+            )
+        if tags_to_add:
+            dynamodb_client.tag_resource(ResourceArn=table_arn, Tags=tags_to_add)
 
     def update(
         self,

@@ -1154,3 +1154,136 @@ def test_dynamodb_online_store_online_read_requested_features_parallel(
         assert "age" in feat_dict
         assert "name" not in feat_dict
         assert "avg_orders_day" not in feat_dict
+
+
+# ---------------------------------------------------------------------------
+# Tests for the diff-based _update_tags (fix for GitHub issue #6418)
+#
+# DynamoDB's TagResource / UntagResource are eventually consistent, so the
+# old approach of "remove all → re-add all" could leave tables tag-less due
+# to the async propagation gap.  The new approach only touches tags that
+# actually need to change.
+# ---------------------------------------------------------------------------
+
+
+def _make_mock_dynamodb_client(
+    current_tags: list[dict[str, str]],
+    table_arn: str = "arn:aws:dynamodb:us-west-2:123456789012:table/test_table",
+):
+    """Helper: create a pure MagicMock DynamoDB client for tag tests.
+    This avoids Moto's authentication issues with DynamoDB tag APIs.
+    """
+    from unittest.mock import MagicMock
+
+    client = MagicMock()
+    # Mock describe_table
+    client.describe_table.return_value = {"Table": {"TableArn": table_arn}}
+    # Mock list_tags_of_resource
+    client.list_tags_of_resource.return_value = {"Tags": current_tags}
+    return client
+
+
+def test_update_tags_no_change_makes_no_api_calls():
+    """Idempotency: calling _update_tags with identical tags must not call
+    untag_resource or tag_resource (avoids unnecessary eventual-consistency exposure).
+    """
+    table_name = f"{TABLE_NAME}_no_change"
+    initial_tags = [{"Key": "env", "Value": "prod"}, {"Key": "team", "Value": "ml"}]
+    client = _make_mock_dynamodb_client(current_tags=initial_tags)
+
+    DynamoDBOnlineStore._update_tags(client, table_name, initial_tags)
+
+    client.untag_resource.assert_not_called()
+    client.tag_resource.assert_not_called()
+
+
+def test_update_tags_adds_new_tags_without_untag():
+    """Adding a new tag key must call tag_resource but NOT untag_resource."""
+    table_name = f"{TABLE_NAME}_add_only"
+    existing = [{"Key": "env", "Value": "prod"}]
+    client = _make_mock_dynamodb_client(current_tags=existing)
+
+    new_tags = [{"Key": "env", "Value": "prod"}, {"Key": "team", "Value": "ml"}]
+    DynamoDBOnlineStore._update_tags(client, table_name, new_tags)
+
+    client.untag_resource.assert_not_called()
+    client.tag_resource.assert_called_once()
+    added = client.tag_resource.call_args[1]["Tags"]
+    assert added == [{"Key": "team", "Value": "ml"}]
+
+
+def test_update_tags_removes_obsolete_tags_only():
+    """Only truly obsolete tag keys (not in new_tags) must be passed to untag_resource."""
+    table_name = f"{TABLE_NAME}_remove_only"
+    existing = [{"Key": "env", "Value": "prod"}, {"Key": "old-key", "Value": "old"}]
+    client = _make_mock_dynamodb_client(current_tags=existing)
+
+    new_tags = [{"Key": "env", "Value": "prod"}]
+    DynamoDBOnlineStore._update_tags(client, table_name, new_tags)
+
+    client.untag_resource.assert_called_once()
+    removed_keys = client.untag_resource.call_args[1]["TagKeys"]
+    assert removed_keys == ["old-key"]
+
+    client.tag_resource.assert_not_called()
+
+
+def test_update_tags_updates_changed_value():
+    """A tag whose value changed must be passed to tag_resource (not untag_resource)."""
+    table_name = f"{TABLE_NAME}_change_value"
+    existing = [{"Key": "env", "Value": "staging"}]
+    client = _make_mock_dynamodb_client(current_tags=existing)
+
+    new_tags = [{"Key": "env", "Value": "prod"}]
+
+    DynamoDBOnlineStore._update_tags(client, table_name, new_tags)
+
+    client.untag_resource.assert_not_called()
+    client.tag_resource.assert_called_once()
+    updated = client.tag_resource.call_args[1]["Tags"]
+    assert updated == [{"Key": "env", "Value": "prod"}]
+
+
+def test_update_tags_full_replace():
+    """Replacing an entire tag set removes old keys and adds new ones correctly."""
+    table_name = f"{TABLE_NAME}_full_replace"
+    existing = [{"Key": "old1", "Value": "v1"}, {"Key": "old2", "Value": "v2"}]
+    client = _make_mock_dynamodb_client(current_tags=existing)
+
+    new_tags = [{"Key": "new1", "Value": "n1"}, {"Key": "new2", "Value": "n2"}]
+
+    DynamoDBOnlineStore._update_tags(client, table_name, new_tags)
+
+    client.untag_resource.assert_called_once()
+    removed = set(client.untag_resource.call_args[1]["TagKeys"])
+    assert removed == {"old1", "old2"}
+
+    client.tag_resource.assert_called_once()
+    added = {t["Key"] for t in client.tag_resource.call_args[1]["Tags"]}
+    assert added == {"new1", "new2"}
+
+
+def test_update_tags_clear_all_tags():
+    """Passing an empty new_tags list removes all existing tags without calling tag_resource."""
+    table_name = f"{TABLE_NAME}_clear_all"
+    existing = [{"Key": "env", "Value": "prod"}]
+    client = _make_mock_dynamodb_client(current_tags=existing)
+
+    DynamoDBOnlineStore._update_tags(client, table_name, [])
+
+    client.untag_resource.assert_called_once()
+    removed = client.untag_resource.call_args[1]["TagKeys"]
+    assert removed == ["env"]
+
+    client.tag_resource.assert_not_called()
+
+
+def test_update_tags_no_existing_tags_no_new_tags():
+    """Both old and new tag sets are empty: no API calls at all."""
+    table_name = f"{TABLE_NAME}_empty_both"
+    client = _make_mock_dynamodb_client(current_tags=[])
+
+    DynamoDBOnlineStore._update_tags(client, table_name, [])
+
+    client.untag_resource.assert_not_called()
+    client.tag_resource.assert_not_called()