Currently, StreamingFileSink is supported only with Hadoop >= 2.7 irrespective of Row/bulk format builder. This restriction is due to truncate is not supported in Hadoop < 2.7
However, BulkFormatBuilder does not use truncate method to restore the file. So the restricting StreamingFileSink.BulkFormatBuilder to be used only with Hadoop >= 2.7 is not necessary.
So requested improvement is to remove the precondition on HadoopRecoverableWriter and allow BulkFormatBuilder (Parquet) to be used in Hadoop 2.6 ( Most of the enterprises still on CDH 5.x)