Haas: Parallel Query v2

Robert Haas describes the many parallelism enhancements in the upcoming PostgreSQL 10 release. "The Gather node introduced in PostgreSQL 9.6 gathers results from all workers in an arbitrary order. That's fine if the data that the workers were producing had no particular ordering anyway, but if each worker is producing sorted output, then it would be nice to gather those results in a way that preserves the sort order. This is what Gather Merge does. It can speed up queries where it's useful for the results of the parallel portion of the plan to have a particular sort order, and where the parallel portion of the plan produces enough rows that performing an ordinary Gather followed by a Sort would be expensive."

Comments (2 posted)