which kind of BlockId should I use?

[william]

When spark is 0.7.3, I use SparkEnv.get.blockManager.getLocal("model") and 
SparkEnv.get.blockManager.put("model", buf, StorageLevel.MEMORY_ONLY, false) to 
cached model object

When I porting to spark 1.0.1, I found  SparkEnv.get.blockManager.getLocal & 
‍SparkEnv.get.blockManager.put's APIs changed to use BlockId instead of String. 


And BlockId has 5 concrete class, which one should I use? None of them have a 
string input parameter.‍‍


Thx