In my mind the two biggest considerations for ORC over Parquet are: 1. Many of the performance improvements provided in the Stinger initiative are dependent on features of the ORC format including block level index for each column. This leads to potentially more efficient I/O allowing Hive to skip reading entire blocks of data if it determines predicate values are not present there. Also the Cost Based Optimizer has the ability to consider column level metadata present in ORC files in order to generate the most efficient graph. 2. ACID transactions are only possible when using ORC as the file format. ... View more

Hi Artem, The default stream id is "default". Check to see if the mapper bolt you mention is declaring a new outputStream. This would occur in the declareOutputFields method of that class. Also, check the collector.emit call within the execute method. The default behavior is to emit on the "default" stream so you can confirm what stream this is emitting on. ... View more