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Charge cpu_tuple_cost * 0.5 for Append and MergeAppend nodes. 

Previously, Append didn't charge anything at all, and MergeAppend
charged only cpu_operator_cost, about half the value used here.  This
change might make MergeAppend plans slightly more likely to be chosen
than before, since this commit increases the assumed cost for Append
-- with default values -- by 0.005 per tuple but MergeAppend by only
0.0025 per tuple.  Since the comparisons required by MergeAppend are
costed separately, it's not clear why MergeAppend needs to be
otherwise more expensive than Append, so hopefully this is OK.

Prior to partition-wise join, it didn't really matter whether or not
an Append node had any cost of its own, because every plan had to use
the same number of Append or MergeAppend nodes and in the same places.
Only the relative cost of Append vs. MergeAppend made a difference.
Now, however, it is possible to avoid some of the Append nodes using a
partition-wise join, so it's worth making an effort.  Pending patches
for partition-wise aggregate care too, because an Append of Aggregate
nodes will incur the Append overhead fewer times than an Aggregate
over an Append.  Although in most cases this change will favor the use
of partition-wise techniques, it does the opposite when the join
cardinality is greater than the sum of the input cardinalities.  Since
this situation arises in an existing regression test, I [rhaas]
adjusted it to keep the overall plan shape approximately the same.

Jeevan Chalke, per a suggestion from David Rowley.  Reviewed by
Ashutosh Bapat.  Some changes by me.  The larger patch series of which
this patch is a part was also reviewed and tested by Antonin Houska,
Rajkumar Raghuwanshi, David Rowley, Dilip Kumar, Konstantin Knizhnik,
Pascal Legrand, Rafia Sabih, and me.

Discussion: http://postgr.es/m/CAKJS1f9UXdk6ZYyqbJnjFO9a9hyHKGW7B=ZRh-rxy9qxfPA5Gw@mail.gmail.com
This commit is contained in:
Robert Haas 2018-02-21 23:09:27 -05:00
parent 38b41f182a
commit 7d8ac9814b
4 changed files with 91 additions and 83 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
src/backend/optimizer/path/costsize.c
View File

@ -100,6 +100,13 @@
#define LOG2(x) (log(x) / 0.693147180559945)
/*
* Append and MergeAppend nodes are less expensive than some other operations
* which use cpu_tuple_cost; instead of adding a separate GUC, estimate the
* per-tuple cost as cpu_tuple_cost multiplied by this value.
*/
#define APPEND_CPU_COST_MULTIPLIER 0.5
double seq_page_cost = DEFAULT_SEQ_PAGE_COST;
double random_page_cost = DEFAULT_RANDOM_PAGE_COST;
@ -1828,10 +1835,6 @@ append_nonpartial_cost(List *subpaths, int numpaths, int parallel_workers)
/*
* cost_append
* Determines and returns the cost of an Append node.
*
* We charge nothing extra for the Append itself, which perhaps is too
* optimistic, but since it doesn't do any selection or projection, it is a
* pretty cheap node.
*/
void
cost_append(AppendPath *apath)
@ -1914,6 +1917,13 @@ cost_append(AppendPath *apath)
apath->first_partial_path,
apath->path.parallel_workers);
}
/*
* Although Append does not do any selection or projection, it's not free;
* add a small per-tuple overhead.
*/
apath->path.total_cost +=
cpu_tuple_cost * APPEND_CPU_COST_MULTIPLIER * apath->path.rows;
}
/*
@ -1968,12 +1978,10 @@ cost_merge_append(Path *path, PlannerInfo *root,
run_cost += tuples * comparison_cost * logN;
/*
* Also charge a small amount (arbitrarily set equal to operator cost) per
* extracted tuple. We don't charge cpu_tuple_cost because a MergeAppend
* node doesn't do qual-checking or projection, so it has less overhead
* than most plan nodes.
* Although MergeAppend does not do any selection or projection, it's not
* free; add a small per-tuple overhead.
*/
run_cost += cpu_operator_cost * tuples;
run_cost += cpu_tuple_cost * APPEND_CPU_COST_MULTIPLIER * tuples;
path->startup_cost = startup_cost + input_startup_cost;
path->total_cost = startup_cost + run_cost + input_total_cost;

136
src/test/regress/expected/partition_join.out
View File

@ -1144,59 +1144,59 @@ INSERT INTO plt1_e SELECT i, i, 'A' || to_char(i/50, 'FM0000') FROM generate_ser
ANALYZE plt1_e;
-- test partition matching with N-way join
EXPLAIN (COSTS OFF)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
QUERY PLAN
--------------------------------------------------------------------------------------
Sort
Sort Key: t1.c, t3.c
-> HashAggregate
Group Key: t1.c, t2.c, t3.c
GroupAggregate
Group Key: t1.c, t2.c, t3.c
-> Sort
Sort Key: t1.c, t3.c
-> Result
-> Append
-> Hash Join
Hash Cond: (t1.c = t2.c)
-> Seq Scan on plt1_p1 t1
-> Hash
-> Hash Join
Hash Cond: (t2.c = ltrim(t3.c, 'A'::text))
Hash Cond: (t1.c = ltrim(t3.c, 'A'::text))
-> Hash Join
Hash Cond: ((t1.b = t2.b) AND (t1.c = t2.c))
-> Seq Scan on plt1_p1 t1
-> Hash
-> Seq Scan on plt2_p1 t2
-> Hash
-> Seq Scan on plt1_e_p1 t3
-> Hash Join
Hash Cond: (t1_1.c = t2_1.c)
-> Seq Scan on plt1_p2 t1_1
-> Hash
-> Hash Join
Hash Cond: (t2_1.c = ltrim(t3_1.c, 'A'::text))
-> Seq Scan on plt1_e_p1 t3
-> Hash Join
Hash Cond: (t1_1.c = ltrim(t3_1.c, 'A'::text))
-> Hash Join
Hash Cond: ((t1_1.b = t2_1.b) AND (t1_1.c = t2_1.c))
-> Seq Scan on plt1_p2 t1_1
-> Hash
-> Seq Scan on plt2_p2 t2_1
-> Hash
-> Seq Scan on plt1_e_p2 t3_1
-> Hash Join
Hash Cond: (t1_2.c = t2_2.c)
-> Seq Scan on plt1_p3 t1_2
-> Hash
-> Hash Join
Hash Cond: (t2_2.c = ltrim(t3_2.c, 'A'::text))
-> Seq Scan on plt1_e_p2 t3_1
-> Hash Join
Hash Cond: (t1_2.c = ltrim(t3_2.c, 'A'::text))
-> Hash Join
Hash Cond: ((t1_2.b = t2_2.b) AND (t1_2.c = t2_2.c))
-> Seq Scan on plt1_p3 t1_2
-> Hash
-> Seq Scan on plt2_p3 t2_2
-> Hash
-> Seq Scan on plt1_e_p3 t3_2
-> Hash
-> Seq Scan on plt1_e_p3 t3_2
(33 rows)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
avg | avg | avg | c | c | c
----------------------+----------------------+-----------------------+------+------+-------
24.0000000000000000 | 24.0000000000000000 | 48.0000000000000000 | 0000 | 0000 | A0000
74.0000000000000000 | 75.0000000000000000 | 148.0000000000000000 | 0001 | 0001 | A0001
124.0000000000000000 | 124.5000000000000000 | 248.0000000000000000 | 0002 | 0002 | A0002
75.0000000000000000 | 75.0000000000000000 | 148.0000000000000000 | 0001 | 0001 | A0001
123.0000000000000000 | 123.0000000000000000 | 248.0000000000000000 | 0002 | 0002 | A0002
174.0000000000000000 | 174.0000000000000000 | 348.0000000000000000 | 0003 | 0003 | A0003
224.0000000000000000 | 225.0000000000000000 | 448.0000000000000000 | 0004 | 0004 | A0004
274.0000000000000000 | 274.5000000000000000 | 548.0000000000000000 | 0005 | 0005 | A0005
225.0000000000000000 | 225.0000000000000000 | 448.0000000000000000 | 0004 | 0004 | A0004
273.0000000000000000 | 273.0000000000000000 | 548.0000000000000000 | 0005 | 0005 | A0005
324.0000000000000000 | 324.0000000000000000 | 648.0000000000000000 | 0006 | 0006 | A0006
374.0000000000000000 | 375.0000000000000000 | 748.0000000000000000 | 0007 | 0007 | A0007
424.0000000000000000 | 424.5000000000000000 | 848.0000000000000000 | 0008 | 0008 | A0008
375.0000000000000000 | 375.0000000000000000 | 748.0000000000000000 | 0007 | 0007 | A0007
423.0000000000000000 | 423.0000000000000000 | 848.0000000000000000 | 0008 | 0008 | A0008
474.0000000000000000 | 474.0000000000000000 | 948.0000000000000000 | 0009 | 0009 | A0009
524.0000000000000000 | 525.0000000000000000 | 1048.0000000000000000 | 0010 | 0010 | A0010
574.0000000000000000 | 574.5000000000000000 | 1148.0000000000000000 | 0011 | 0011 | A0011
525.0000000000000000 | 525.0000000000000000 | 1048.0000000000000000 | 0010 | 0010 | A0010
573.0000000000000000 | 573.0000000000000000 | 1148.0000000000000000 | 0011 | 0011 | A0011
(12 rows)
-- joins where one of the relations is proven empty
@ -1289,59 +1289,59 @@ INSERT INTO pht1_e SELECT i, i, 'A' || to_char(i/50, 'FM0000') FROM generate_ser
ANALYZE pht1_e;
-- test partition matching with N-way join
EXPLAIN (COSTS OFF)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
QUERY PLAN
--------------------------------------------------------------------------------------
Sort
Sort Key: t1.c, t3.c
-> HashAggregate
Group Key: t1.c, t2.c, t3.c
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
QUERY PLAN
--------------------------------------------------------------------------------------------
GroupAggregate
Group Key: t1.c, t2.c, t3.c
-> Sort
Sort Key: t1.c, t3.c
-> Result
-> Append
-> Hash Join
Hash Cond: (t1.c = t2.c)
-> Seq Scan on pht1_p1 t1
-> Hash
-> Hash Join
Hash Cond: (t2.c = ltrim(t3.c, 'A'::text))
Hash Cond: (t1.c = ltrim(t3.c, 'A'::text))
-> Hash Join
Hash Cond: ((t1.b = t2.b) AND (t1.c = t2.c))
-> Seq Scan on pht1_p1 t1
-> Hash
-> Seq Scan on pht2_p1 t2
-> Hash
-> Seq Scan on pht1_e_p1 t3
-> Hash
-> Seq Scan on pht1_e_p1 t3
-> Hash Join
Hash Cond: (t1_1.c = t2_1.c)
-> Seq Scan on pht1_p2 t1_1
Hash Cond: (ltrim(t3_1.c, 'A'::text) = t1_1.c)
-> Seq Scan on pht1_e_p2 t3_1
-> Hash
-> Hash Join
Hash Cond: (t2_1.c = ltrim(t3_1.c, 'A'::text))
-> Seq Scan on pht2_p2 t2_1
Hash Cond: ((t1_1.b = t2_1.b) AND (t1_1.c = t2_1.c))
-> Seq Scan on pht1_p2 t1_1
-> Hash
-> Seq Scan on pht1_e_p2 t3_1
-> Seq Scan on pht2_p2 t2_1
-> Hash Join
Hash Cond: (t1_2.c = t2_2.c)
-> Seq Scan on pht1_p3 t1_2
Hash Cond: (ltrim(t3_2.c, 'A'::text) = t1_2.c)
-> Seq Scan on pht1_e_p3 t3_2
-> Hash
-> Hash Join
Hash Cond: (t2_2.c = ltrim(t3_2.c, 'A'::text))
-> Seq Scan on pht2_p3 t2_2
Hash Cond: ((t1_2.b = t2_2.b) AND (t1_2.c = t2_2.c))
-> Seq Scan on pht1_p3 t1_2
-> Hash
-> Seq Scan on pht1_e_p3 t3_2
-> Seq Scan on pht2_p3 t2_2
(33 rows)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
avg | avg | avg | c | c | c
----------------------+----------------------+-----------------------+------+------+-------
24.0000000000000000 | 24.0000000000000000 | 48.0000000000000000 | 0000 | 0000 | A0000
74.0000000000000000 | 75.0000000000000000 | 148.0000000000000000 | 0001 | 0001 | A0001
124.0000000000000000 | 124.5000000000000000 | 248.0000000000000000 | 0002 | 0002 | A0002
75.0000000000000000 | 75.0000000000000000 | 148.0000000000000000 | 0001 | 0001 | A0001
123.0000000000000000 | 123.0000000000000000 | 248.0000000000000000 | 0002 | 0002 | A0002
174.0000000000000000 | 174.0000000000000000 | 348.0000000000000000 | 0003 | 0003 | A0003
224.0000000000000000 | 225.0000000000000000 | 448.0000000000000000 | 0004 | 0004 | A0004
274.0000000000000000 | 274.5000000000000000 | 548.0000000000000000 | 0005 | 0005 | A0005
225.0000000000000000 | 225.0000000000000000 | 448.0000000000000000 | 0004 | 0004 | A0004
273.0000000000000000 | 273.0000000000000000 | 548.0000000000000000 | 0005 | 0005 | A0005
324.0000000000000000 | 324.0000000000000000 | 648.0000000000000000 | 0006 | 0006 | A0006
374.0000000000000000 | 375.0000000000000000 | 748.0000000000000000 | 0007 | 0007 | A0007
424.0000000000000000 | 424.5000000000000000 | 848.0000000000000000 | 0008 | 0008 | A0008
375.0000000000000000 | 375.0000000000000000 | 748.0000000000000000 | 0007 | 0007 | A0007
423.0000000000000000 | 423.0000000000000000 | 848.0000000000000000 | 0008 | 0008 | A0008
474.0000000000000000 | 474.0000000000000000 | 948.0000000000000000 | 0009 | 0009 | A0009
524.0000000000000000 | 525.0000000000000000 | 1048.0000000000000000 | 0010 | 0010 | A0010
574.0000000000000000 | 574.5000000000000000 | 1148.0000000000000000 | 0011 | 0011 | A0011
525.0000000000000000 | 525.0000000000000000 | 1048.0000000000000000 | 0010 | 0010 | A0010
573.0000000000000000 | 573.0000000000000000 | 1148.0000000000000000 | 0011 | 0011 | A0011
(12 rows)
--

4
src/test/regress/expected/subselect.out
View File

@ -235,7 +235,7 @@ SELECT *, pg_typeof(f1) FROM
explain verbose select '42' union all select '43';
QUERY PLAN
-------------------------------------------------
Append (cost=0.00..0.04 rows=2 width=32)
Append (cost=0.00..0.05 rows=2 width=32)
-> Result (cost=0.00..0.01 rows=1 width=32)
Output: '42'::text
-> Result (cost=0.00..0.01 rows=1 width=32)
@ -245,7 +245,7 @@ explain verbose select '42' union all select '43';
explain verbose select '42' union all select 43;
QUERY PLAN
------------------------------------------------
Append (cost=0.00..0.04 rows=2 width=4)
Append (cost=0.00..0.05 rows=2 width=4)
-> Result (cost=0.00..0.01 rows=1 width=4)
Output: 42
-> Result (cost=0.00..0.01 rows=1 width=4)

8
src/test/regress/sql/partition_join.sql
View File

@ -213,8 +213,8 @@ ANALYZE plt1_e;
-- test partition matching with N-way join
EXPLAIN (COSTS OFF)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM plt1 t1, plt2 t2, plt1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
-- joins where one of the relations is proven empty
EXPLAIN (COSTS OFF)
@ -258,8 +258,8 @@ ANALYZE pht1_e;
-- test partition matching with N-way join
EXPLAIN (COSTS OFF)
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
SELECT avg(t1.a), avg(t2.b), avg(t3.a + t3.b), t1.c, t2.c, t3.c FROM pht1 t1, pht2 t2, pht1_e t3 WHERE t1.b = t2.b AND t1.c = t2.c AND ltrim(t3.c, 'A') = t1.c GROUP BY t1.c, t2.c, t3.c ORDER BY t1.c, t2.c, t3.c;
--
-- multiple levels of partitioning