Best way to determine # of workers

I'm building some elasticity into my model and I'd like to know when my workers have come online. It appears at present that the API only supports getting information about applications. Is there a good way to determine how many workers are available? -- View this message in context:

Passing parameters to spark SQL

Given a SQLContext (or HiveContext) is it possible to pass in parameters to a query. There are several reasons why this makes sense, including loss of data type during conversion to string, SQL injection, etc. But currently, it appears that SQLContext.sql() only takes a single parameter which is