David Steele <da...@pgmasters.net> wrote: > On 12/22/17 6:13 AM, Thomas Munro wrote: > > On Fri, Dec 22, 2017 at 10:45 PM, Antonin Houska <a...@cybertec.at> wrote: > >> try_partial_hashjoin_path() passes constant true to for the parallel_hash > >> argument of initial_cost_hashjoin(). Shouldn't it instead pass the > >> parallel_hash argument that it receives? > > > > Thanks. Yeah. When initial_cost_hashjoin() calls > > get_parallel_divisor() on a non-partial inner path I think it would > > return 1.0, so no damage was done there, but when > > ExecChooseHashTableSize() receives try_combined_work_mem == true it > > might underestimate the number of batches required for a partial hash > > join without parallel hash, because it would incorrectly assume that a > > single batch join could use the combined work_mem budget. This was > > quite well hidden because ExecHashTableCreate() calls > > ExecChooseHashTableSize() again (rather than reusing the results from > > planning time), so the bad nbatch estimate doesn't show up anywhere.
> Does this look right to you? Yes, this is what I meant. The patch applies cleanly and the code compiles well. > If so, can you sign up as a reviewer and mark it Ready for Committer? Done. Actually I think it'd be nice if the "parallel_hash" argument was mentioned in the header comment of initial_cost_hashjoin() function, but not sure this is worth returning the patch to the author. -- Antonin Houska Cybertec Schönig & Schönig GmbH Gröhrmühlgasse 26, A-2700 Wiener Neustadt Web: https://www.cybertec-postgresql.com
