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
@ -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;
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
-> 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;
-- 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;
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;
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;
Robert Haas
8 years ago