database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-03 20:02:46 +03:00
Code Activity

Tweak planner and executor to avoid doing ExecProject() in table scan

Browse Source 
nodes where it's not really necessary.  In many cases where the scan node
is not the topmost plan node (eg, joins, aggregation), it's possible to
just return the table tuple directly instead of generating an intermediate
projection tuple.  In preliminary testing, this reduced the CPU time
needed for 'SELECT COUNT(*) FROM foo' by about 10%.
This commit is contained in:
Tom Lane
2003-02-03 15:07:08 +00:00
parent 0d3e36b668
commit 4cff59d8d5
12 changed files with 476 additions and 230 deletions
Download Patch File Download Diff File Expand all files Collapse all files

78
src/backend/optimizer/plan/createplan.c
View File

@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.133 2003/01/22 00:07:00 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.134 2003/02/03 15:07:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -34,6 +34,7 @@
static Scan *create_scan_plan(Query *root, Path *best_path);
static bool use_physical_tlist(RelOptInfo *rel);
static Join *create_join_plan(Query *root, JoinPath *best_path);
static Append *create_append_plan(Query *root, AppendPath *best_path);
static Result *create_result_plan(Query *root, ResultPath *best_path);
@ -185,15 +186,41 @@ create_plan(Query *root, Path *best_path)
static Scan *
create_scan_plan(Query *root, Path *best_path)
{
Scan *plan;
List *tlist = best_path->parent->targetlist;
RelOptInfo *rel = best_path->parent;
List *tlist;
List *scan_clauses;
Scan *plan;
/*
* For table scans, rather than using the relation targetlist (which is
* only those Vars actually needed by the query), we prefer to generate a
* tlist containing all Vars in order. This will allow the executor to
* optimize away projection of the table tuples, if possible. (Note that
* planner.c may replace the tlist we generate here, forcing projection to
* occur.)
*/
if (use_physical_tlist(rel))
{
int resdomno = 1;
List *v;
tlist = NIL;
foreach(v, rel->varlist)
{
Var *var = (Var *) lfirst(v);
tlist = lappend(tlist, create_tl_element(var, resdomno));
resdomno++;
}
}
else
tlist = rel->targetlist;
/*
* Extract the relevant restriction clauses from the parent relation;
* the executor must apply all these restrictions during the scan.
*/
scan_clauses = get_actual_clauses(best_path->parent->baserestrictinfo);
scan_clauses = get_actual_clauses(rel->baserestrictinfo);
/* Sort clauses into best execution order */
scan_clauses = order_qual_clauses(root, scan_clauses);
@ -241,6 +268,47 @@ create_scan_plan(Query *root, Path *best_path)
return plan;
}
/*
* use_physical_tlist
* Decide whether to use a tlist matching relation structure,
* rather than only those Vars actually referenced.
*/
static bool
use_physical_tlist(RelOptInfo *rel)
{
List *t;
/*
* Currently, can't do this for subquery or function scans. (This
* is mainly because we don't set up the necessary info when creating
* their RelOptInfo nodes.)
*/
if (rel->rtekind != RTE_RELATION)
return false;
/*
* Can't do it with inheritance cases either (mainly because Append
* doesn't project).
*/
if (rel->reloptkind != RELOPT_BASEREL)
return false;
/*
* Can't do it if any system columns are requested, either. (This could
* possibly be fixed but would take some fragile assumptions in setrefs.c,
* I think.)
*/
foreach(t, rel->targetlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(t);
Var *var = (Var *) tle->expr;
if (!var || !IsA(var, Var))
return false; /* probably can't happen */
if (var->varattno <= 0)
return false; /* system column! */
}
return true;
}
/*
* create_join_plan
* Create a join plan for 'best_path' and (recursively) plans for its
@ -399,7 +467,7 @@ create_material_plan(Query *root, MaterialPath *best_path)
subplan = create_plan(root, best_path->subpath);
plan = make_material(best_path->path.parent->targetlist, subplan);
plan = make_material(subplan->targetlist, subplan);
copy_path_costsize(&plan->plan, (Path *) best_path);