Serialize concurrent datasource publications

src/govoplan_datasources/backend/service.py

@@ -7,7 +7,7 @@ from collections.abc import Mapping, Sequence
 from dataclasses import dataclass, replace
 from typing import Any, cast
 
-from sqlalchemy import exists, func, or_, select
+from sqlalchemy import exists, func, or_, select, text
 from sqlalchemy.orm import Session
 
 from govoplan_core.audit.logging import audit_event
@@ -98,6 +98,12 @@ class SqlDatasourceProvider:
     ) -> DatasourcePublicationResult:
         db, api_principal = _publication_context(session, principal)
         prepared = _prepare_publication(request)
+        _lock_publication_identity(
+            db,
+            tenant_id=api_principal.tenant_id,
+            producer_module=prepared.producer_module,
+            idempotency_key=prepared.idempotency_key,
+        )
         existing = _existing_publication_result(
             db,
             tenant_id=api_principal.tenant_id,
@@ -1649,6 +1655,44 @@ def _validate_publication_identity(
             )
 
 
+def _publication_lock_key(
+    *,
+    tenant_id: str,
+    producer_module: str,
+    idempotency_key: str,
+) -> int:
+    payload = (
+        f"govoplan.datasources.publication\0{tenant_id}\0"
+        f"{producer_module}\0{idempotency_key}"
+    ).encode("utf-8")
+    return int.from_bytes(
+        hashlib.sha256(payload).digest()[:8],
+        "big",
+        signed=True,
+    )
+
+
+def _lock_publication_identity(
+    session: Session,
+    *,
+    tenant_id: str,
+    producer_module: str,
+    idempotency_key: str,
+) -> None:
+    if session.get_bind().dialect.name != "postgresql":
+        return
+    session.execute(
+        text("SELECT pg_advisory_xact_lock(:key)"),
+        {
+            "key": _publication_lock_key(
+                tenant_id=tenant_id,
+                producer_module=producer_module,
+                idempotency_key=idempotency_key,
+            )
+        },
+    )
+
+
 def _existing_publication_result(
     session: Session,
     *,