Warning message: In is(object, Cl) : error while fetching rows R

I am unable to fetch all rows from mysql using R. There are around 900000 rows need to fetch but R is fetching only around 500000 rows. I am getting below warning.

  > response = fetch(res ,1000000)
    Warning message:
    In is(object, Cl) : error while fetching rows

Any help would be appreciated.