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. -- Thomas Munro http://www.enterprisedb.com
fix.patch
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