Thank you very much for the testing of the patch, Ahsan! At Wed, 15 Jan 2020 15:41:04 -0500, Bruce Momjian <br...@momjian.us> wrote in > On Tue, Jan 14, 2020 at 02:37:48PM +0500, Ahsan Hadi wrote: > > Summary > > The patch is pretty good, it works well when there were little data back to > > the parent node. The patch doesn’t provide parallel FDW scan, it ensures > > that child nodes can send data to parent in parallel but the parent can only > > sequennly process the data from data nodes.
"Parallel scan" at the moment means multiple workers fetch unique blocks from *one* table in an arbitrated manner. In this sense "parallel FDW scan" means multiple local workers fetch unique bundles of tuples from *one* foreign table, which means it is running on a single session. That doesn't offer an advantage. If parallel query processing worked in worker-per-table mode, especially on partitioned tables, maybe the current FDW would work without much of modification. But I believe asynchronous append on foreign tables on a single process is far resource-effective and moderately faster than parallel append. > > Providing there is no performance degrdation for non FDW append queries, > > I would recomend to consider this patch as an interim soluton while we are > > waiting for parallel FDW scan. > > Wow, these are very impressive results! Thanks. -- Kyotaro Horiguchi NTT Open Source Software Center