On Fri, Jan 03, 2020 at 09:33:35AM -0500, Jeff Janes wrote:
> Of course this doesn't really answer your question, as the
> separately-reported costs of a bitmap heap and bitmap index scan are
> unlikely to match what the costs would be of a regular index scan, if they
> were reported separately.
I think the cost of index component of bitmap scan would be exactly the same
as the cost of the original indexscan.
>> Or maybe explain should report it.
>
> I wouldn't be optimistic about getting such a backwards-incompatible change
> accepted (plus it would surely add some small accounting overhead, which
> again would probably not be acceptable). But if you do enough tuning work,
> perhaps it would be worth carrying an out-of-tree patch to implement that.
> I wouldn't be so interested in writing such a patch, but would be
> interested in using one were it available somewhere.
I did the attached in the simplest possible way. If it's somehow possible get
the path's index_total_cost from the plan, then there'd be no additional
overhead.
Justin
>From 52ac676bdef1aa0a1fa18520a69d267fbb93eb19 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@xxxxxxxxxxxxx>
Date: Fri, 3 Jan 2020 09:53:31 -0600
Subject: [PATCH v1] explain: show index_total_cost
---
src/backend/commands/explain.c | 3 +++
src/backend/optimizer/plan/createplan.c | 1 +
src/include/nodes/plannodes.h | 1 +
3 files changed, 5 insertions(+)
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 0910d91..8973c86 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -1614,6 +1614,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
if (plan->qual)
show_instrumentation_count("Rows Removed by Filter", 1,
planstate, es);
+ if (es->costs && es->verbose) // && verbose ?
+ ExplainPropertyFloat("Index Total Cost", NULL,
+ planstate->plan->indextotalcost, 2, es);
break;
case T_IndexOnlyScan:
show_scan_qual(((IndexOnlyScan *) plan)->indexqual,
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index dff826a..c0419bc 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -2924,6 +2924,7 @@ create_indexscan_plan(PlannerInfo *root,
best_path->indexscandir);
copy_generic_path_info(&scan_plan->plan, &best_path->path);
+ ((Plan *)scan_plan)->indextotalcost = best_path->indextotalcost;
return scan_plan;
}
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 32c0d87..711c9d8 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -122,6 +122,7 @@ typedef struct Plan
*/
Cost startup_cost; /* cost expended before fetching any tuples */
Cost total_cost; /* total cost (assuming all tuples fetched) */
+ Cost indextotalcost; /* total cost of index */
/*
* planner's estimate of result size of this plan step
--
2.7.4
