fix: close session before doing long latency operation (#22306)

api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py

@@ -144,6 +144,8 @@ class KnowledgeRetrievalNode(LLMNode):
                 error=str(e),
                 error_type=type(e).__name__,
             )
+        finally:
+            db.session.close()
 
     def _fetch_dataset_retriever(self, node_data: KnowledgeRetrievalNodeData, query: str) -> list[dict[str, Any]]:
         available_datasets = []
@@ -171,6 +173,9 @@ class KnowledgeRetrievalNode(LLMNode):
             .all()
         )
 
+        # avoid blocking at retrieval
+        db.session.close()
+
         for dataset in results:
             # pass if dataset is not available
             if not dataset: