Hi Mr.Pyhalov. > From: Alexander Pyhalov <a.pyha...@postgrespro.ru> > Sent: Friday, July 14, 2023 10:40 PM > 1) In foreign_join_ok() should we set fpinfo->user if > fpinfo->check_partial_aggregate_support is set like it's done for > fpinfo->use_remote_estimate? It seems we can end up with fpinfo->user > fpinfo->= > NULL if use_remote_estimate is not set. You are right. I will modify this patch according to your advice. Thank you for advice.
> 2) It seeems we found an additional issue with original patch, which > is present in current one. I'm attaching a patch which seems to fix > it, but I'm not quite sure in it. Thank you for pointing out the issue. If a query's group-by clause contains variable based expression(not variable) and the query's select clause contains another expression, the partial aggregate could be unsafe to push down. An example of such queries: SELECT (b/2)::numeric, avg(a), max(a), count(*) FROM pagg_tab GROUP BY b/2 Your patch disables partial aggregate pushdown for such queries. I'll see if we can modify the patch to safely do a partial aggregate pushdown for such queries as well. Such a query expects the variable in the select clause expression to be included in the target of the grouped rel (let see make_partial_grouping_target), but the original groupby clause has no reference to this variable, this seems to be the direct cause(let see foreign_grouping_ok). I will examine whether a safe pushdown can be achieved by matching the groupby clause information referenced by foreign_grouping_ok with the grouped rel target information. Sincerely yours, Yuuki Fujii -- Yuuki Fujii Information Technology R&D Center Mitsubishi Electric Corporation
