Distributed columnar data set subset retrieval

An apparatus includes a processor to: within each reading thread, retrieve a data set part and corresponding part metadata from storage device(s), analyze row group metadata for each row group within the data set part to identify candidate row group(s) meeting specified criteria, and store the candidate row group(s) and corresponding row group metadata within a data buffer of a queue; operate the queue as a FIFO buffer; within each provision thread, retrieve one of multiple row groups and corresponding metadata from within the data buffer, use information in the metadata to identify rows meeting the criteria, and provide those rows to the requesting device or an application; and in response to each instance of storage of a data set part within a data buffer of the queue, analyze the availability of storage space and/or of processing resources to determine whether to dynamically adjust the quantity of reading threads.