[Spark R]could not allocate memory (2048 Mb) in C function 'R_AllocStringBuffer'

[Todd]

I am launching spark R with following script:

./sparkR --driver-memory 12G

and I try to load a local 3G csv file with following code,

> a=read.transactions("/home/admin/datamining/data.csv",sep="\t",format="single",cols=c(1,2))

but I encounter an error:  could not allocate memory (2048 Mb) in C function 
'R_AllocStringBuffer'

I have allocated 12G memory,not sure why it complains could not allocate 2G 
memory.

Could someone help me? Thanks!