Hi，
I'm a system architect work for china merchant bank, I want to use
calcite to do some federated queries across different databases and push
calculations to spark, so I enable the spark option but get an no pointer
exception.
I think the problem is I didn't configure the spark adaptor, but
couldn't find any introduction or documents talking about it, except some
test specs.
So my question is, is there any way to push calculations into spark,
or it just unavailable in current version.
Forgive my bad English.
