[SPARK-15159][SPARKR] SparkR SparkSession API

## What changes were proposed in this pull request?

This PR introduces the new SparkSession API for SparkR.
`sparkR.session.getOrCreate()` and `sparkR.session.stop()`

"getOrCreate" is a bit unusual in R but it's important to name this clearly.

SparkR implementation should
- SparkSession is the main entrypoint (vs SparkContext; due to limited functionality supported with SparkContext in SparkR)
- SparkSession replaces SQLContext and HiveContext (both a wrapper around SparkSession, and because of API changes, supporting all 3 would be a lot more work)
- Changes to SparkSession is mostly transparent to users due to SPARK-10903
- Full backward compatibility is expected - users should be able to initialize everything just in Spark 1.6.1 (`sparkR.init()`), but with deprecation warning
- Mostly cosmetic changes to parameter list - users should be able to move to `sparkR.session.getOrCreate()` easily
- An advanced syntax with named parameters (aka varargs aka "...") is supported; that should be closer to the Builder syntax that is in Scala/Python (which unfortunately does not work in R because it will look like this: `enableHiveSupport(config(config(master(appName(builder(), "foo"), "local"), "first", "value"), "next, "value"))`
- Updating config on an existing SparkSession is supported, the behavior is the same as Python, in which config is applied to both SparkContext and SparkSession
- Some SparkSession changes are not matched in SparkR, mostly because it would be breaking API change: `catalog` object, `createOrReplaceTempView`
- Other SQLContext workarounds are replicated in SparkR, eg. `tables`, `tableNames`
- `sparkR` shell is updated to use the SparkSession entrypoint (`sqlContext` is removed, just like with Scale/Python)
- All tests are updated to use the SparkSession entrypoint
- A bug in `read.jdbc` is fixed

TODO
- [x] Add more tests
- [ ] Separate PR - update all roxygen2 doc coding example
- [ ] Separate PR - update SparkR programming guide

## How was this patch tested?

unit tests, manual tests

shivaram sun-rui rxin

Author: Felix Cheung <felixcheung_m@hotmail.com>
Author: felixcheung <felixcheung_m@hotmail.com>

Closes #13635 from felixcheung/rsparksession.

1 files changed, 6 insertions, 6 deletions

diff --git a/R/pkg/inst/profile/shell.R b/R/pkg/inst/profile/shell.R
index 90a3761e41..8a8111a8c5 100644
--- a/R/pkg/inst/profile/shell.R
+++ b/R/pkg/inst/profile/shell.R
@@ -18,17 +18,17 @@
 .First <- function() {
   home <- Sys.getenv("SPARK_HOME")
   .libPaths(c(file.path(home, "R", "lib"), .libPaths()))
-  Sys.setenv(NOAWT=1)
+  Sys.setenv(NOAWT = 1)
 
   # Make sure SparkR package is the last loaded one
   old <- getOption("defaultPackages")
   options(defaultPackages = c(old, "SparkR"))
 
-  sc <- SparkR::sparkR.init()
-  assign("sc", sc, envir=.GlobalEnv)
-  sqlContext <- SparkR::sparkRSQL.init(sc)
+  spark <- SparkR::sparkR.session()
+  assign("spark", spark, envir = .GlobalEnv)
+  sc <- SparkR:::callJStatic("org.apache.spark.sql.api.r.SQLUtils", "getJavaSparkContext", spark)
+  assign("sc", sc, envir = .GlobalEnv)
   sparkVer <- SparkR:::callJMethod(sc, "version")
-  assign("sqlContext", sqlContext, envir=.GlobalEnv)
   cat("\n Welcome to")
   cat("\n")
   cat("    ____              __", "\n")
@@ -43,5 +43,5 @@
   cat("    /_/", "\n")
   cat("\n")
 
-  cat("\n Spark context is available as sc, SQL context is available as sqlContext\n")
+  cat("\n SparkSession available as 'spark'.\n")
 }