We have a RAC env and want to connect to a specific instance, the tns entry I used is something like mydb1 = (DESCRIPTION = (SDU = 32768) (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(Host = node1)(Port = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = mydb) (INSTANCE_NAME = mydb1) ) ) But it still connected to the other instance. I think the server side balance is configured, so I am wondering whether the server side balance will balance the connect regardless of the client side tnsnames.ora setting. One colleague told me to delete the line (SERVICE_NAME = mydb), but it still didn't work.