This is for a notebook env that has the spark session/context bootstrapped for the user. There are settings that are user specific so not all of those can go into the spark-defaults.conf - such settings need to be dynamically applied when creating the session/context.
In Scala/Python, I would bootstrap a "spark" handle similar to what spark-shell / psyspark-shell startup scripts do. In my case the bootstrapped object could be of a wrapper class that took care of whatever customization I needed while exposing the regular SparkSession scala/python API. The user uses this object as he/she would use a regular SparkSession to submit work to the Spark cluster. Since I am certain there is no other way for users to perform Spark work except to go via the bootstrapped object, I can achieve my objective of delaying creation of SparkSession/Context until a call comes to my custom spark object. If I want to do the same in R, and let users write SparkR code as they normally would, but bootstrapping a SparkContext/Session for them, then I hit the issues as I explained earlier. There is no single entry point for SparkContext/Session in SparkR API and so to achieve lazy creation of SparkContext/session, it looks like the only option is to do some trickery with the SparkR:::.sparkREnv$.sparkRjsc and SparkR:::.sparkREnv$.sparkRsession vars. Regards, Vin. On Sat, Apr 22, 2017 at 3:33 AM, Felix Cheung <felixcheun...@hotmail.com> wrote: > How would you handle this in Scala? > > If you are adding a wrapper func like getSparkSession for Scala, and have > your users call it, can't you do that same in SparkR? After all, while true > you don't need a SparkSession object to call the R API, someone still needs > to call sparkR.session() to initial the current session? > > Also what Spark environment you want to customize? > > Can these be set in environment variables or via spark-defaults.conf > spark.apache.org/docs/latest/configuration.html#dynamically-loading-spark- > properties > > > _____________________________ > From: Vin J <winjos...@gmail.com> > Sent: Friday, April 21, 2017 2:22 PM > Subject: [SparkR] - options around setting up SparkSession / SparkContext > To: <dev@spark.apache.org> > > > > > 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. > > > > >
