diff --git a/conf/infinity_mapping.json b/conf/infinity_mapping.json
index 5f7ed80f2..893e18632 100644
--- a/conf/infinity_mapping.json
+++ b/conf/infinity_mapping.json
@@ -39,5 +39,6 @@
 	"doc_type_kwd": {"type": "varchar", "default": "", "analyzer": "whitespace-#"},
 	"toc_kwd": {"type": "varchar", "default": "", "analyzer": "whitespace-#"},
 	"raptor_kwd": {"type": "varchar", "default": "", "analyzer": "whitespace-#"},
-	"raptor_layer_int": {"type": "integer", "default": 0}
+	"raptor_layer_int": {"type": "integer", "default": 0},
+	"extra": {"type": "varchar", "default": ""}
 }
diff --git a/rag/utils/infinity_conn.py b/rag/utils/infinity_conn.py
index 7ffd9f13d..9407ab11a 100644
--- a/rag/utils/infinity_conn.py
+++ b/rag/utils/infinity_conn.py
@@ -438,6 +438,16 @@ class InfinityConnection(InfinityConnectionBase):
                             d[k] = json.dumps(v)
                         else:
                             d[k] = v
+                    elif k == "extra":
+                        # RAPTOR writes {"raptor_method": ...} as a dict; Infinity's
+                        # `extra` column is varchar so we serialize on the write path.
+                        # The read path (raptor_utils._as_extra_dict) already accepts
+                        # both dict and JSON-string. Other backends (OceanBase JSON
+                        # column, ES/OpenSearch) keep dict shape — this is Infinity-only.
+                        if isinstance(v, dict):
+                            d[k] = json.dumps(v)
+                        else:
+                            d[k] = v if v else ""
                     elif k == "kb_id":
                         if isinstance(d[k], list):
                             d[k] = d[k][0]  # since d[k] is a list, but we need a str