Context Switching in R Server

R code tends to be very memory intensive as R processes primarily in memory. If you want R to perform well, you want as much memory as you can get your hands on to run your code, especially with larger datasets. This is a problem as many individual laptops have pitifully low memory capacity, and unless you have a computer with say as much memory as you can put in this one, if you are analyzing large datasets you may run out of memory. If a new computer is not in the budget, why not develop on the server? You may be thinking that there is no way the administrator of the box is going to provide you the means to be able to use the server memory. Well, if you have a SQL Server 2016 with R Server installed, chances are you can use the memory capacity of the server by connecting your R process to run on it from your computer, without the need to install anything on the server.

Microsoft’s R Server contains some specialized functions which are not part of the standard CRAN R installation. One of the ScaleR functions, RxInSqlServer will allow code to be processed on the server from the client. To make this work, you must have R Server and R Client installed. If you are doing a test on a local machine, you will need both R Client and R Server installed on that computer.

How to use the Server Memory not Local memory for Running R

If you are developing R in your IDE of choice, either R Studio or Visual Studio with R Tools, here is the code you need to make that work, which includes code running on the server

#First you will need to install ('RevoScaleR') if not there already as context switching is included in that library
if (!require("RevoScaleR")) {
install.packages("RevoScaleR")
}
#Load the library
library(RevoScaleR)
#Create a connection to your SQL Server 2016 server instance. Note the double slashes which I needed to identify the instance name
#
sqlConnString <- "Driver=SQL Server;Server=DevSQLServer\\SS2016;Database=TestR;Uid=ReadDataID;Pwd=readd@t@!!!"
#Set the variable containing RxInSQLServer. Note All specific R Server libraries start with Rx
#
serverside #Set the Compute context to SQL server. After this the code will run using Server Memory, not local memory
#
rxSetComputeContext(serverside)
#Check to see what the compute context is. Not this is for informational purposes. You do not need to do this to make anything work.
#
rxGetComputeContext()
#If you want to change the compute context back to your computer run this command
#rxSetComputeContext("local")
#Until the context is switched back, I am now running on the server, not locally.
#Here I am going to take a look at a table in my TestR database called AirlineDemoSmall
#
sqlsampleTable <- "AirlineDemoSmall"
#
sqlPlaneDS<- RxSqlServerData(connectionString = sqlConnString, verbose = 1,table = sqlsampleTable )
#To take a look at the content of the data, I am going to take a look at 30 rows in table in my TestR database called AirlineDemoSmall
#
rxGetInfo(data = sqlPlaneDS, getVarInfo = TRUE, numRows = 10)
#To visually investigate the data, this command will plot a histogram displaying the frequencies of values in #one of the columns, CRSDepTime
#
rxHistogram(~CRSDepTime, data = sqlPlaneDS)

Here’s the output I get back in the R interactive Window.

Data Source: SQLSERVER
Number of variables: 3
Variable information:
Var 1: ArrDelay, Type: character
Var 2: CRSDepTime, Type: numeric
Var 3: DayOfWeek, Type: character
Data (10 rows starting with row 1):
ArrDelay CRSDepTime DayOfWeek
1       -14 16.283333   Monday
2       -1   6.166667   Monday
3       -2   7.000000   Monday
4         0 10.266666   Monday
5         0 13.483334   Monday
6       -10 16.833334   Monday
7       -10 19.949999   Monday
8       350 14.650001   Monday
9       292   9.416667   Monday
10       M   6.000000   Monday

RxHistogram

RxHistogram

Let me know if you found this post helpful, by posting a comment. Thanks also to Mario, who asked me about context switching which gave me the idea to answer his questions on this site. If you are interested in seeing more information about SQL Server and R, please subscribe as I tend to answer more of the questions I receive here.

 

 

 

 

Yours Always

Ginger Grant

Data aficionado et SQL Raconteur

3 comments on “Context Switching in R Server

  1. Hikari

    Hello,

    Sure that the code is correct and complete? I don’t see where you use RxInSqlServer.

    It’s unbelievable, but I have so many problems with SQL context (and all of them are based on MS tutorials). All my codes run perfectly fine in local context, but when moved to server context I get los of errors at different stages (rxDataStep, rxPredict, etc.).

  2. Mario

    Hi Ginger,

    I keep getting the following message:

    Warning in install.packages :
    package ‘RevoScaleR’ is not available (for R version 3.3.2)

    Any suggestions?

    Cheers,

    –Mario

    1. Ginger Grant

      Mario —

      Yes I have seen the warning message about RevoScaleR not being available. The first thing I would do to resolve it is to install SQL Server 2016 SP1 CU1. This contains an important fix to SQL Server which resolves an incompatibility issue with the latest R Client. You’ll also need to install the latest version. Here’s a link to that as well https://msdn.microsoft.com/en-us/microsoft-r/r-client-get-started

      Installing both of these applications should resolve your driver problems. Let me know how it works out.

      Regards,
      Ginger

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