🐛(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/api/serializers.py

@@ -7,7 +7,6 @@ from base64 import b64decode
 from os.path import splitext
 
 from django.conf import settings
-from django.db import connection, transaction
 from django.db.models import Q
 from django.utils.functional import lazy
 from django.utils.text import slugify
@@ -24,6 +23,7 @@ from core.services.converter_services import (
     ConversionError,
     Converter,
 )
+from core.utils.treebeard import create_tree_node_with_retry
 
 
 class UserSerializer(serializers.ModelSerializer):
@@ -467,18 +467,12 @@ class ServerCreateDocumentSerializer(serializers.Serializer):
                 {"content": ["Could not convert content"]}
             ) from err
 
-        with transaction.atomic():
-            # locks the table to ensure safe concurrent access
-            with connection.cursor() as cursor:
-                cursor.execute(
-                    f'LOCK TABLE "{models.Document._meta.db_table}" '  # noqa: SLF001
-                    "IN SHARE ROW EXCLUSIVE MODE;"
-                )
-
-            document = models.Document.add_root(
+        document = create_tree_node_with_retry(
+            lambda: models.Document.add_root(
                 title=validated_data["title"],
                 creator=user,
             )
+        )
 
         if user:
             # Associate the document with the pre-existing user

src/backend/core/api/viewsets.py

@@ -68,6 +68,7 @@ from core.services.search_indexers import (
 )
 from core.tasks.mail import send_ask_for_access_mail
 from core.utils.paths import filter_descendants
+from core.utils.treebeard import create_tree_node_with_retry
 from core.utils.users import users_sharing_documents_with
 from core.utils.yjs import extract_attachments
 
@@ -706,18 +707,12 @@ class DocumentViewSet(
                     {"file": ["Could not convert file content"]}
                 ) from err
 
-        with transaction.atomic():
-            # locks the table to ensure safe concurrent access
-            with connection.cursor() as cursor:
-                cursor.execute(
-                    f'LOCK TABLE "{models.Document._meta.db_table}" '  # noqa: SLF001
-                    "IN SHARE ROW EXCLUSIVE MODE;"
-                )
-
-            obj = models.Document.add_root(
+        obj = create_tree_node_with_retry(
+            lambda: models.Document.add_root(
                 creator=self.request.user,
                 **serializer.validated_data,
             )
+        )
         serializer.instance = obj
         models.DocumentAccess.objects.create(
             document=obj,
@@ -1021,16 +1016,12 @@ class DocumentViewSet(
             )
             serializer.is_valid(raise_exception=True)
 
-            with transaction.atomic():
-                # "select_for_update" locks the table to ensure safe concurrent access
-                locked_parent = models.Document.objects.select_for_update().get(
-                    pk=document.pk
-                )
-
-                child_document = locked_parent.add_child(
+            child_document = create_tree_node_with_retry(
+                lambda: document.add_child(
                     creator=request.user,
                     **serializer.validated_data,
                 )
+            )
 
             # Set the created instance to the serializer
             serializer.instance = child_document