update pool size (#545)

update pool size

Author: CaralHsi

src/memos/graph_dbs/polardb.py

@@ -145,7 +145,7 @@ def __init__(self, config: PolarDBGraphDBConfig):
         # Create connection pool
         self.connection_pool = psycopg2.pool.ThreadedConnectionPool(
             minconn=5,
-            maxconn=2000,
+            maxconn=100,
             host=host,
             port=port,
             user=user,