🐛(backend) replace document creation table locks with retry strategy

We have situation where the number of locks in the database can increase
dangerously creating deadlock situation. To remove this situation we
decided to change the strategy to manage document creation concurrency.
We decided to use a retry strategy, trying to create the document
multiple times while a usable path is found. To avoid having an
inifinite loop, we use a max_attempts counter configurable using the
setting TREEBEARD_PATH_COMPUTE_RETRY_MAX_ATTEMPTS

src/backend/core/tests/test_utils_create_tree_node_with_retry.py

@@ -0,0 +1,89 @@
+"""Tests for the create_tree_node_with_retry utils."""
+
+from unittest import mock
+
+from django.core.exceptions import ValidationError as DjangoValidationError
+from django.db import IntegrityError
+
+import pytest
+
+from core.factories import UserFactory
+from core.models import Document
+from core.utils.treebeard import _is_tree_path_collision, create_tree_node_with_retry
+
+pytestmark = pytest.mark.django_db
+
+
+@pytest.mark.parametrize(
+    "exc",
+    [
+        DjangoValidationError({"path": "not unique"}),
+        IntegrityError("impress_document_path_key"),
+    ],
+)
+def test_utils_create_tree_node_with_retry_exceed_max_attempts(settings, exc):
+    """Test exceeding the max attempts should reraise the exception."""
+
+    settings.TREEBEARD_PATH_COMPUTE_RETRY_MAX_ATTEMPTS = 2
+
+    create_fn = mock.MagicMock()
+    create_fn.side_effect = exc
+
+    with (
+        pytest.raises(exc.__class__),
+        mock.patch(
+            "core.utils.treebeard._is_tree_path_collision"
+        ) as mock__is_tree_path_collision,
+    ):
+        mock__is_tree_path_collision.side_effect = _is_tree_path_collision
+        create_tree_node_with_retry(create_fn)
+
+    mock__is_tree_path_collision.assert_called()
+    assert mock__is_tree_path_collision.call_count == 2
+    assert create_fn.call_count == 2
+
+
+@pytest.mark.parametrize(
+    "exc",
+    [
+        DjangoValidationError({"foo": "bar"}),
+        IntegrityError("not handled"),
+    ],
+)
+def test_utils_create_tree_node_with_retry_exceed_exception_not_handled(settings, exc):
+    """Test with an exception not handled should return reraise it immediately."""
+
+    settings.TREEBEARD_PATH_COMPUTE_RETRY_MAX_ATTEMPTS = 2
+
+    create_fn = mock.MagicMock()
+    create_fn.side_effect = exc
+
+    with (
+        pytest.raises(exc.__class__),
+        mock.patch(
+            "core.utils.treebeard._is_tree_path_collision"
+        ) as mock__is_tree_path_collision,
+    ):
+        mock__is_tree_path_collision.side_effect = _is_tree_path_collision
+        create_tree_node_with_retry(create_fn)
+
+    mock__is_tree_path_collision.assert_called()
+    assert mock__is_tree_path_collision.call_count == 1
+    assert create_fn.call_count == 1
+
+
+def test_utils_create_tree_node_with_retry_success():
+    """Test executing successfully the create_fn callback."""
+
+    user = UserFactory()
+
+    document = create_tree_node_with_retry(
+        lambda: Document.add_root(
+            creator=user,
+            title="success",
+        )
+    )
+
+    assert isinstance(document, Document)
+    assert document.title == "success"
+    assert document.path is not None