skip LLM summary when entity descriptions haven't changed

Check incoming descriptions against what's already on the node.
If nothing new was added, reuse the existing summary instead of
calling the LLM again. Saves a lot of time on re-ingestion.

Author: ndcorder

lightrag/operate.py

@@ -1770,6 +1770,31 @@ async def _merge_nodes_then_upsert(
         )
         description_list = [fallback_description]
 
+    # Skip LLM summary if no new descriptions were added (re-ingestion optimisation)
+    if already_node and already_description:
+        existing_descriptions = set(
+            d.strip()
+            for d in already_description
+            if d.strip()
+        )
+        incoming_descriptions = set(
+            d.strip()
+            for d in sorted_descriptions
+            if d.strip()
+        )
+        if incoming_descriptions and incoming_descriptions.issubset(existing_descriptions):
+            logger.debug(
+                f"Entity '{entity_name}': no new descriptions, skipping LLM summary"
+            )
+            node_data = dict(already_node)
+            node_data["source_id"] = source_id
+            node_data["file_path"] = GRAPH_FIELD_SEP.join(
+                list(dict.fromkeys(already_file_paths + [dp.get("file_path") for dp in nodes_data if dp.get("file_path")]))
+            )
+            await knowledge_graph_inst.upsert_node(entity_name, node_data=node_data)
+            node_data["entity_name"] = entity_name
+            return node_data
+
     # Check for cancellation before LLM summary
     if pipeline_status is not None and pipeline_status_lock is not None:
         async with pipeline_status_lock:

tests/test_skip_unchanged_summary.py

@@ -0,0 +1,144 @@
+# test_skip_unchanged_summary.py
+
+import pytest
+from unittest.mock import AsyncMock, patch
+from lightrag.utils import GRAPH_FIELD_SEP
+
+
+def _make_global_config(**overrides):
+    cfg = {
+        "source_ids_limit_method": "FIFO",
+        "max_source_ids_per_entity": 100,
+        "max_file_paths": 50,
+        "file_path_more_placeholder": "more",
+    }
+    cfg.update(overrides)
+    return cfg
+
+
+@pytest.fixture
+def mock_kg_with_existing_person():
+    kg = AsyncMock()
+    kg.get_node = AsyncMock(return_value={
+        "entity_type": "PERSON",
+        "source_id": "doc1",
+        "file_path": "file1.pdf",
+        "description": f"Alice is a person{GRAPH_FIELD_SEP}Alice works at Acme",
+    })
+    kg.upsert_node = AsyncMock()
+    return kg
+
+
+@pytest.mark.asyncio
+async def test_skip_summary_when_no_new_descriptions(mock_kg_with_existing_person):
+    from lightrag.operate import _merge_nodes_then_upsert
+
+    nodes_data = [
+        {
+            "entity_type": "PERSON",
+            "source_id": "doc1",
+            "file_path": "file1.pdf",
+            "description": "Alice is a person",
+        },
+        {
+            "entity_type": "PERSON",
+            "source_id": "doc1",
+            "file_path": "file1.pdf",
+            "description": "Alice works at Acme",
+        },
+    ]
+
+    with patch("lightrag.operate._handle_entity_relation_summary") as mock_summary:
+        await _merge_nodes_then_upsert(
+            entity_name="Alice",
+            nodes_data=nodes_data,
+            knowledge_graph_inst=mock_kg_with_existing_person,
+            entity_vdb=None,
+            global_config=_make_global_config(),
+        )
+        mock_summary.assert_not_called()
+
+    mock_kg_with_existing_person.upsert_node.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_calls_summary_when_new_descriptions(mock_kg_with_existing_person):
+    from lightrag.operate import _merge_nodes_then_upsert
+
+    nodes_data = [
+        {
+            "entity_type": "PERSON",
+            "source_id": "doc2",
+            "file_path": "file2.pdf",
+            "description": "Alice is the CEO of Acme",
+        },
+    ]
+
+    with patch("lightrag.operate._handle_entity_relation_summary") as mock_summary:
+        mock_summary.return_value = ("Alice is a person and CEO of Acme", True)
+        await _merge_nodes_then_upsert(
+            entity_name="Alice",
+            nodes_data=nodes_data,
+            knowledge_graph_inst=mock_kg_with_existing_person,
+            entity_vdb=None,
+            global_config=_make_global_config(),
+        )
+        mock_summary.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_calls_summary_for_new_entity():
+    from lightrag.operate import _merge_nodes_then_upsert
+
+    mock_kg = AsyncMock()
+    mock_kg.get_node = AsyncMock(return_value=None)
+    mock_kg.upsert_node = AsyncMock()
+
+    nodes_data = [
+        {
+            "entity_type": "ORG",
+            "source_id": "doc1",
+            "file_path": "file1.pdf",
+            "description": "Acme Corp makes widgets",
+        },
+    ]
+
+    with patch("lightrag.operate._handle_entity_relation_summary") as mock_summary:
+        mock_summary.return_value = ("Acme Corp makes widgets", True)
+        await _merge_nodes_then_upsert(
+            entity_name="Acme",
+            nodes_data=nodes_data,
+            knowledge_graph_inst=mock_kg,
+            entity_vdb=None,
+            global_config=_make_global_config(),
+        )
+        mock_summary.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_skip_preserves_existing_description(mock_kg_with_existing_person):
+    from lightrag.operate import _merge_nodes_then_upsert
+
+    existing_desc = f"Alice is a person{GRAPH_FIELD_SEP}Alice works at Acme"
+
+    nodes_data = [
+        {
+            "entity_type": "PERSON",
+            "source_id": "doc1",
+            "file_path": "file1.pdf",
+            "description": "Alice is a person",
+        },
+    ]
+
+    with patch("lightrag.operate._handle_entity_relation_summary"):
+        await _merge_nodes_then_upsert(
+            entity_name="Alice",
+            nodes_data=nodes_data,
+            knowledge_graph_inst=mock_kg_with_existing_person,
+            entity_vdb=None,
+            global_config=_make_global_config(),
+        )
+
+    call_kwargs = mock_kg_with_existing_person.upsert_node.call_args
+    upserted_data = call_kwargs.kwargs.get("node_data", call_kwargs[1].get("node_data"))
+    assert upserted_data["description"] == existing_desc