diff --git a/src/memos/graph_dbs/polardb.py b/src/memos/graph_dbs/polardb.py
index 20e02bd0c..de05185d2 100644
--- a/src/memos/graph_dbs/polardb.py
+++ b/src/memos/graph_dbs/polardb.py
@@ -151,6 +151,10 @@ def __init__(self, config: PolarDBGraphDBConfig):
             user=user,
             password=password,
             dbname=self.db_name,
+            connect_timeout=60,  # Connection timeout in seconds
+            keepalives_idle=40,  # Seconds of inactivity before sending keepalive (should be < server idle timeout)
+            keepalives_interval=15,  # Seconds between keepalive retries
+            keepalives_count=5,  # Number of keepalive retries before considering connection dead
         )
 
         # Keep a reference to the pool for cleanup
@@ -179,7 +183,7 @@ def _get_config_value(self, key: str, default=None):
         else:
             return getattr(self.config, key, default)
 
-    def _get_connection(self):
+    def _get_connection_old(self):
         """Get a connection from the pool."""
         if self._pool_closed:
             raise RuntimeError("Connection pool has been closed")
@@ -188,7 +192,60 @@ def _get_connection(self):
         conn.autocommit = True
         return conn
 
+    def _get_connection(self):
+        """Get a connection from the pool."""
+        if self._pool_closed:
+            raise RuntimeError("Connection pool has been closed")
+
+        max_retries = 3
+        for attempt in range(max_retries):
+            try:
+                conn = self.connection_pool.getconn()
+
+                # Check if connection is closed
+                if conn.closed != 0:
+                    # Connection is closed, close it explicitly and try again
+                    try:
+                        conn.close()
+                    except Exception as e:
+                        logger.warning(f"Failed to close connection: {e}")
+                    if attempt < max_retries - 1:
+                        continue
+                    else:
+                        raise RuntimeError("Pool returned a closed connection")
+
+                # Set autocommit for PolarDB compatibility
+                conn.autocommit = True
+                return conn
+            except Exception as e:
+                if attempt >= max_retries - 1:
+                    raise RuntimeError(f"Failed to get a valid connection from pool: {e}") from e
+                continue
+
     def _return_connection(self, connection):
+        """Return a connection to the pool."""
+        if not self._pool_closed and connection:
+            try:
+                # Check if connection is closed
+                if hasattr(connection, "closed") and connection.closed != 0:
+                    # Connection is closed, just close it and don't return to pool
+                    try:
+                        connection.close()
+                    except Exception as e:
+                        logger.warning(f"Failed to close connection: {e}")
+                    return
+
+                # Connection is valid, return to pool
+                self.connection_pool.putconn(connection)
+            except Exception as e:
+                # If putconn fails, close the connection
+                logger.warning(f"Failed to return connection to pool: {e}")
+                try:
+                    connection.close()
+                except Exception as e:
+                    logger.warning(f"Failed to close connection: {e}")
+
+    def _return_connection_old(self, connection):
         """Return a connection to the pool."""
         if not self._pool_closed and connection:
             self.connection_pool.putconn(connection)
@@ -1834,7 +1891,7 @@ def export_graph(
                     if include_embedding and embedding_json is not None:
                         properties["embedding"] = embedding_json
 
-                    nodes.append(self._parse_node(properties))
+                    nodes.append(self._parse_node(json.loads(properties[1])))
 
         except Exception as e:
             logger.error(f"[EXPORT GRAPH - NODES] Exception: {e}", exc_info=True)
diff --git a/src/memos/memories/textual/tree.py b/src/memos/memories/textual/tree.py
index 53628d075..dea3cc1ab 100644
--- a/src/memos/memories/textual/tree.py
+++ b/src/memos/memories/textual/tree.py
@@ -260,7 +260,7 @@ def get_relevant_subgraph(
                 center_id=core_id, depth=depth, center_status=center_status
             )
 
-            if not subgraph["core_node"]:
+            if subgraph is None or not subgraph["core_node"]:
                 logger.info(f"Skipping node {core_id} (inactive or not found).")
                 continue
 
@@ -281,9 +281,9 @@ def get_relevant_subgraph(
                 {"id": core_id, "score": score, "core_node": core_node, "neighbors": neighbors}
             )
 
-        top_core = cores[0]
+        top_core = cores[0] if cores else None
         return {
-            "core_id": top_core["id"],
+            "core_id": top_core["id"] if top_core else None,
             "nodes": list(all_nodes.values()),
             "edges": [{"source": f, "target": t, "type": ty} for (f, t, ty) in all_edges],
         }