Re: Problems with plan estimates in postgres_fdw

Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:

> (2019/02/15 21:46), Antonin Houska wrote:
> > ok, I understand now. I assume that the patch
> >
> > https://www.postgresql.org/message-id/5C66A056.60007%40lab.ntt.co.jp
> >
> > obsoletes the code snippet we discussed above.
> 
> Sorry, I don't understand this.  Could you elaborate on that?

I thought that the assignments

+ 			startup_cost += outerrel->reltarget->cost.startup;

and

+ 			run_cost += outerrel->reltarget->cost.per_tuple * input_rows;

in the patch you posted in
https://www.postgresql.org/message-id/5C66A056.60007%40lab.ntt.co.jp do
replace

+			startup_cost += foreignrel->reltarget->cost.startup;

and

+			run_cost += foreignrel->reltarget->cost.per_tuple * rows;

respectively, which you originally included in the following part of
0001-postgres_fdw-Perform-UPPERREL_ORDERED-step-remotely-v3.patch:

@@ -2829,6 +2872,22 @@ estimate_path_cost_size(PlannerInfo *root,
 			run_cost += foreignrel->reltarget->cost.per_tuple * rows;
 		}
 
+		/*
+		 * If this is an UPPERREL_ORDERED step on the final scan/join
+		 * relation, the costs obtained from the cache wouldn't yet contain
+		 * the eval cost for the final scan/join target, which would have been
+		 * updated by apply_scanjoin_target_to_paths(); add the eval cost now.
+		 */
+		if (fpextra && !IS_UPPER_REL(foreignrel))
+		{
+			/* The costs should have been obtained from the cache. */
+			Assert(fpinfo->rel_startup_cost >= 0 &&
+				   fpinfo->rel_total_cost >= 0);
+
+			startup_cost += foreignrel->reltarget->cost.startup;
+			run_cost += foreignrel->reltarget->cost.per_tuple * rows;
+		}
+
 		/*
 		 * Without remote estimates, we have no real way to estimate the cost
 		 * of generating sorted output.  It could be free if the query plan


-- 
Antonin Houska
Cybertec Schönig & Schönig GmbH
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