Multi-stage parallelization model for scalable execution of partitioned row limiting

Abstract

A database command includes an order-by-key, a hierarchy of partition keys, a top number of partitions to return for each partitioning key level, and a number of rows to return for each partition key value combination. Communications are performed between the worker processes and a query coordinator for initial sorts of the partition keys until all of the worker processes can be used to perform the remaining sorts while avoiding duplicate rows. The results of the initial sorts are distributed to the worker processes in a manner that maintains rows of unique partition key combinations on respective individual worker processes. Each worker process constructs the remaining sorts locally using the rows it receives.