I need to make an R environment available where the SparkSession/SparkContext needs to be setup a specific way. The user simply accesses this environment and executes his/her code. If the user code does not access any Spark functions, I do not want to create a SparkContext unnecessarily.
In Scala/Python environments, the user can't access spark without first referencing SparkContext / SparkSession classes. So the above (lazy and/or custom SparkSession/Context creation) is easily met by offering sparkContext/sparkSession handles to the user that are either wrappers on Spark's classes or have lazy evaluation semantics. This way only when the user accesses these handles to sparkContext/Session will the SparkSession/Context actually get set up without the user needing to know all the details about initing the SparkContext/Session. However, achieving the same doesn't appear to be so straightforward in R. >From what I see, executing sparkR.session(...) sets up private variables in SparkR:::.sparkREnv (.sparkRjsc , .sparkRsession). The way SparkR api works, a user doesn't need a handle to the spark session as such. Executing functions like so: "df <- as.DataFrame(..)" implicitly access the private vars in SparkR:::.sparkREnv to get access to the sparkContext etc that are expected to have been created by a prior call to sparkR.session()/sparkR.init() etc. Therefore, to inject any custom/lazy behavior into this I don't see a way except through having my code (that sits outside of Spark) apply a delayedAssign() or a makeActiveBinding( ) on SparkR:::.sparkRsession / .sparkRjsc variables. This way when spark code internally references them, my wrapper/lazy code gets executed to do whatever I need done. However, I am seeing some limitations of applying even this approach to SparkR - it will not work unless some minor changes are made in the SparkR code. But, before I opened a PR that would do these changes in SparkR I wanted to check if there was a better way to achieve this? I am far less than an R expert, and could be missing something here. If you'd rather see this in a JIRA and a PR, let me know and I'll go ahead and open one. Regards, Vin.
