Use TScan.batchSize (available in newer Thrift versions)

[wbolster]

Relevant Thrift API:

/**
 * A Scan object is used to specify scanner parameters when opening a scanner.
 */
struct TScan {
  1:optional Text startRow,
  2:optional Text stopRow,
  3:optional i64 timestamp,
  4:optional list<Text> columns,
  5:optional i32 caching,
  6:optional Text filterString,
  7:optional i32 batchSize,
  8:optional bool sortColumns
}