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Commit6d2c8c0

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Drop cheap-startup-cost paths during add_path() if we don't need them.
We can detect whether the planner top level is going to care at all aboutcheap startup cost (it will only do so if query_planner's tuple_fractionargument is greater than zero). If it isn't, we might as well discardpaths immediately whose only advantage over others is cheap startup cost.This turns out to get rid of quite a lot of paths in complex queries ---I saw planner runtime reduction of more than a third on one large query.Since add_path isn't currently passed the PlannerInfo "root", the easiestway to tell it whether to do this was to add a bool flag to RelOptInfo.That's a bit redundant, since all relations in a given query level willhave the same setting. But in the future it's possible that we'd refinethe control decision to work on a per-relation basis, so this seems likea good arrangement anyway.Per my suggestion of a few months ago.
1 parent4da6439 commit6d2c8c0

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6 files changed

+36
-11
lines changed

6 files changed

+36
-11
lines changed

‎src/backend/nodes/outfuncs.c‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1733,6 +1733,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
17331733
WRITE_BITMAPSET_FIELD(relids);
17341734
WRITE_FLOAT_FIELD(rows,"%.0f");
17351735
WRITE_INT_FIELD(width);
1736+
WRITE_BOOL_FIELD(consider_startup);
17361737
WRITE_NODE_FIELD(reltargetlist);
17371738
WRITE_NODE_FIELD(pathlist);
17381739
WRITE_NODE_FIELD(ppilist);

‎src/backend/optimizer/util/pathnode.c‎

Lines changed: 19 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -139,14 +139,18 @@ compare_fractional_path_costs(Path *path1, Path *path2,
139139
* total cost, we just say that their costs are "different", since neither
140140
* dominates the other across the whole performance spectrum.
141141
*
142+
* If consider_startup is false, then we don't care about keeping paths with
143+
* good startup cost, so we'll never return COSTS_DIFFERENT.
144+
*
142145
* This function also includes special hacks to support a policy enforced
143146
* by its sole caller, add_path(): paths that have any parameterization
144147
* cannot win comparisons on the grounds of having cheaper startup cost,
145148
* since we deem only total cost to be of interest for a parameterized path.
146149
* (Unparameterized paths are more common, so we check for this case last.)
147150
*/
148151
staticPathCostComparison
149-
compare_path_costs_fuzzily(Path*path1,Path*path2,doublefuzz_factor)
152+
compare_path_costs_fuzzily(Path*path1,Path*path2,doublefuzz_factor,
153+
boolconsider_startup)
150154
{
151155
/*
152156
* Check total cost first since it's more likely to be different; many
@@ -155,7 +159,8 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor)
155159
if (path1->total_cost>path2->total_cost*fuzz_factor)
156160
{
157161
/* path1 fuzzily worse on total cost */
158-
if (path2->startup_cost>path1->startup_cost*fuzz_factor&&
162+
if (consider_startup&&
163+
path2->startup_cost>path1->startup_cost*fuzz_factor&&
159164
path1->param_info==NULL)
160165
{
161166
/* ... but path2 fuzzily worse on startup, so DIFFERENT */
@@ -167,7 +172,8 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor)
167172
if (path2->total_cost>path1->total_cost*fuzz_factor)
168173
{
169174
/* path2 fuzzily worse on total cost */
170-
if (path1->startup_cost>path2->startup_cost*fuzz_factor&&
175+
if (consider_startup&&
176+
path1->startup_cost>path2->startup_cost*fuzz_factor&&
171177
path2->param_info==NULL)
172178
{
173179
/* ... but path1 fuzzily worse on startup, so DIFFERENT */
@@ -177,6 +183,7 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor)
177183
returnCOSTS_BETTER1;
178184
}
179185
/* fuzzily the same on total cost */
186+
/* (so we may as well compare startup cost, even if !consider_startup) */
180187
if (path1->startup_cost>path2->startup_cost*fuzz_factor&&
181188
path2->param_info==NULL)
182189
{
@@ -360,6 +367,9 @@ set_cheapest(RelOptInfo *parent_rel)
360367
* reduce the number of parameterized paths that are kept. See discussion
361368
* in src/backend/optimizer/README.
362369
*
370+
* Another policy that is enforced here is that we only consider cheap
371+
* startup cost to be interesting if parent_rel->consider_startup is true.
372+
*
363373
* The pathlist is kept sorted by total_cost, with cheaper paths
364374
* at the front. Within this routine, that's simply a speed hack:
365375
* doing it that way makes it more likely that we will reject an inferior
@@ -423,7 +433,8 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
423433
* Do a fuzzy cost comparison with 1% fuzziness limit.(XXX does this
424434
* percentage need to be user-configurable?)
425435
*/
426-
costcmp=compare_path_costs_fuzzily(new_path,old_path,1.01);
436+
costcmp=compare_path_costs_fuzzily(new_path,old_path,1.01,
437+
parent_rel->consider_startup);
427438

428439
/*
429440
* If the two paths compare differently for startup and total cost,
@@ -488,8 +499,10 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
488499
remove_old= true;/* new dominates old */
489500
elseif (new_path->rows>old_path->rows)
490501
accept_new= false;/* old dominates new */
491-
elseif (compare_path_costs_fuzzily(new_path,old_path,
492-
1.0000000001)==COSTS_BETTER1)
502+
elseif (compare_path_costs_fuzzily(new_path,
503+
old_path,
504+
1.0000000001,
505+
parent_rel->consider_startup)==COSTS_BETTER1)
493506
remove_old= true;/* new dominates old */
494507
else
495508
accept_new= false;/* old equals or

‎src/backend/optimizer/util/relnode.c‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -99,6 +99,8 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
9999
rel->relids=bms_make_singleton(relid);
100100
rel->rows=0;
101101
rel->width=0;
102+
/* cheap startup cost is interesting iff not all tuples to be retrieved */
103+
rel->consider_startup= (root->tuple_fraction>0);
102104
rel->reltargetlist=NIL;
103105
rel->pathlist=NIL;
104106
rel->ppilist=NIL;
@@ -354,6 +356,8 @@ build_join_rel(PlannerInfo *root,
354356
joinrel->relids=bms_copy(joinrelids);
355357
joinrel->rows=0;
356358
joinrel->width=0;
359+
/* cheap startup cost is interesting iff not all tuples to be retrieved */
360+
joinrel->consider_startup= (root->tuple_fraction>0);
357361
joinrel->reltargetlist=NIL;
358362
joinrel->pathlist=NIL;
359363
joinrel->ppilist=NIL;

‎src/include/nodes/relation.h‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -299,6 +299,8 @@ typedef struct PlannerInfo
299299
* clauses have been applied (ie, output rows of a plan for it)
300300
*width - avg. number of bytes per tuple in the relation after the
301301
*appropriate projections have been done (ie, output width)
302+
*consider_startup - true if there is any value in keeping paths for
303+
* this rel on the basis of having cheap startup cost
302304
*reltargetlist - List of Var and PlaceHolderVar nodes for the values
303305
*we need to output from this relation.
304306
*List is in no particular order, but all rels of an
@@ -405,6 +407,9 @@ typedef struct RelOptInfo
405407
doublerows;/* estimated number of result tuples */
406408
intwidth;/* estimated avg width of result tuples */
407409

410+
/* per-relation planner control flags */
411+
boolconsider_startup;/* keep cheap-startup-cost paths? */
412+
408413
/* materialization information */
409414
List*reltargetlist;/* Vars to be output by scan of relation */
410415
List*pathlist;/* Path structures */

‎src/test/regress/expected/join.out‎

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -3437,6 +3437,7 @@ select v.* from
34373437

34383438
create temp table dual();
34393439
insert into dual default values;
3440+
analyze dual;
34403441
select v.* from
34413442
(int8_tbl x left join (select q1,(select coalesce(q2,0)) q2 from int8_tbl) y on x.q2 = y.q1)
34423443
left join int4_tbl z on z.f1 = x.q2,
@@ -3446,21 +3447,21 @@ select v.* from
34463447
123 |
34473448
456 |
34483449
123 | 4567890123456789
3449-
4567890123456789 | 123
3450+
4567890123456789 |-4567890123456789
34503451
123 | 4567890123456789
34513452
4567890123456789 | 4567890123456789
34523453
123 | 4567890123456789
3453-
4567890123456789 | -4567890123456789
34543454
4567890123456789 | 123
3455-
123 | 456
34563455
4567890123456789 | 123
34573456
123 | 4567890123456789
3458-
4567890123456789 | 4567890123456789
34593457
4567890123456789 | 123
3458+
123 | 456
34603459
4567890123456789 | 4567890123456789
3460+
4567890123456789 | -4567890123456789
34613461
4567890123456789 | 4567890123456789
34623462
4567890123456789 | 4567890123456789
3463-
4567890123456789 | -4567890123456789
3463+
4567890123456789 | 4567890123456789
3464+
4567890123456789 | 123
34643465
4567890123456789 |
34653466
-4567890123456789 |
34663467
(20 rows)

‎src/test/regress/sql/join.sql‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -937,6 +937,7 @@ select v.* from
937937
lateral (selectx.q1,y.q1union allselectx.q2,y.q2) v(vx,vy);
938938
create temp table dual();
939939
insert into dual defaultvalues;
940+
analyze dual;
940941
select v.*from
941942
(int8_tbl xleft join (select q1,(select coalesce(q2,0)) q2from int8_tbl) yonx.q2=y.q1)
942943
left join int4_tbl zonz.f1=x.q2,

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