North Korea and China Relations

In September of this year Kim Jong-Il's youngest son and heir apparent, Kim Jong-Un, was elevated to the status of four-star general and vice chairman of the Central Militray Comission. Also in the same month Kim Jong-Il was "reelected" as president of North Korea. Shortly after Chinese state councillor and public security minister, Meng Jianzhu, warmly congratulated Kim Jong-Il on the "the successful solution of the issue of succession to the Korean revolution." Considering North Korea's volatility, I wonder if it really is in the Chinese's best interest to align themselves with such an isolationist country.