[SPARK-12318][SPARKR] Save mode in SparkR should be error by default

shivaram  Please help review.

Author: Jeff Zhang <zjffdu@apache.org>

Closes #10290 from zjffdu/SPARK-12318.

2 files changed, 13 insertions, 6 deletions

diff --git a/R/pkg/R/DataFrame.R b/R/pkg/R/DataFrame.R
index 764597d1e3..380a13fe2b 100644
--- a/R/pkg/R/DataFrame.R
+++ b/R/pkg/R/DataFrame.R
@@ -1886,7 +1886,7 @@ setMethod("except",
 #' @param df A SparkSQL DataFrame
 #' @param path A name for the table
 #' @param source A name for external data source
-#' @param mode One of 'append', 'overwrite', 'error', 'ignore' save mode
+#' @param mode One of 'append', 'overwrite', 'error', 'ignore' save mode (it is 'error' by default)
 #'
 #' @family DataFrame functions
 #' @rdname write.df
@@ -1903,7 +1903,7 @@ setMethod("except",
 #' }
 setMethod("write.df",
           signature(df = "DataFrame", path = "character"),
-          function(df, path, source = NULL, mode = "append", ...){
+          function(df, path, source = NULL, mode = "error", ...){
             if (is.null(source)) {
               sqlContext <- get(".sparkRSQLsc", envir = .sparkREnv)
               source <- callJMethod(sqlContext, "getConf", "spark.sql.sources.default",
@@ -1928,7 +1928,7 @@ setMethod("write.df",
 #' @export
 setMethod("saveDF",
           signature(df = "DataFrame", path = "character"),
-          function(df, path, source = NULL, mode = "append", ...){
+          function(df, path, source = NULL, mode = "error", ...){
             write.df(df, path, source, mode, ...)
           })
 
@@ -1951,7 +1951,7 @@ setMethod("saveDF",
 #' @param df A SparkSQL DataFrame
 #' @param tableName A name for the table
 #' @param source A name for external data source
-#' @param mode One of 'append', 'overwrite', 'error', 'ignore' save mode
+#' @param mode One of 'append', 'overwrite', 'error', 'ignore' save mode (it is 'error' by default)
 #'
 #' @family DataFrame functions
 #' @rdname saveAsTable
@@ -1968,7 +1968,7 @@ setMethod("saveDF",
 setMethod("saveAsTable",
           signature(df = "DataFrame", tableName = "character", source = "character",
                     mode = "character"),
-          function(df, tableName, source = NULL, mode="append", ...){
+          function(df, tableName, source = NULL, mode="error", ...){
             if (is.null(source)) {
               sqlContext <- get(".sparkRSQLsc", envir = .sparkREnv)
               source <- callJMethod(sqlContext, "getConf", "spark.sql.sources.default",
diff --git a/docs/sparkr.md b/docs/sparkr.md
index 01148786b7..9ddd2eda3f 100644
--- a/docs/sparkr.md
+++ b/docs/sparkr.md
@@ -148,7 +148,7 @@ printSchema(people)
 </div>
 
 The data sources API can also be used to save out DataFrames into multiple file formats. For example we can save the DataFrame from the previous example
-to a Parquet file using `write.df`
+to a Parquet file using `write.df` (Until Spark 1.6, the default mode for writes was `append`. It was changed in Spark 1.7 to `error` to match the Scala API)
 
 <div data-lang="r"  markdown="1">
 {% highlight r %}
@@ -387,3 +387,10 @@ The following functions are masked by the SparkR package:
 Since part of SparkR is modeled on the `dplyr` package, certain functions in SparkR share the same names with those in `dplyr`. Depending on the load order of the two packages, some functions from the package loaded first are masked by those in the package loaded after. In such case, prefix such calls with the package name, for instance, `SparkR::cume_dist(x)` or `dplyr::cume_dist(x)`.
   
 You can inspect the search path in R with [`search()`](https://stat.ethz.ch/R-manual/R-devel/library/base/html/search.html)
+
+
+# Migration Guide
+
+## Upgrading From SparkR 1.6 to 1.7
+
+ - Until Spark 1.6, the default mode for writes was `append`. It was changed in Spark 1.7 to `error` to match the Scala API.