Yeah I guess I was thinking that the deserialization of the CombineInputSplit doesn't have to include deserializing the wrapped splits, it could wait until it has access to a configuration before trying to pull the wrapped splits out. If implementing Configurable magically hands you the configuration, then go for it :)

Just curious, what does SerializationFactory and friends do that you don't get directly with the Writable API or java.io.Serializable? Aren't all InputSplits Writable?

So where you are using a SerializationFactory, couldn't you just delegate to each InputSplit's writeFields method instead? Then you don't even need the config, you can just do:

```
for split in splits:
  split.write(dataout)
```
right?