Add support for Hive/Impala

It would be really nice for Caravel to have support for Hive/Impala. There is a nice package called Impyla that provides a SQLAlchemy interface to Hive and Impala.

I am testing it out with Caravel, seems to be working so far with Hive. I can connect to my Hive database, there is a problem where SQLAlchemy tries to run a select version() as the first query, as this is not a valid Hive function, it causes an immediate failure. Once I resolve this I will open a pull request.

[evinhas]

I added an extra in the Superset “create database connection” for passing some connection arguments:

{
    "metadata_params": {},
    "engine_params": {
		"connect_args": {
		"auth_mechanism": "GSSAPI",
		"user" : "put_your_user_here",
		"password" : "None" }
}
}

So I introduced a connection URL as following one:

impala://impala_host:21050/impala_database

And it worked

Note: I had run a kinit before to connect.

[joshwalters]

Raised a pull request to fix this issue with Impala here: https://github.com/cloudera/impyla/pull/191

I have tested the Impyla fix, and verified that I now have a working Hive/Impala connection in Caravel. Once the Impyla fix is in, I will make a pull request against Caravel to add it.