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Optimize joins when the inner relation can be proven unique.

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If there can certainly be no more than one matching inner row for a given
outer row, then the executor can move on to the next outer row as soon as
it's found one match; there's no need to continue scanning the inner
relation for this outer row.  This saves useless scanning in nestloop
and hash joins.  In merge joins, it offers the opportunity to skip
mark/restore processing, because we know we have not advanced past the
first possible match for the next outer row.

Of course, the devil is in the details: the proof of uniqueness must
depend only on joinquals (not otherquals), and if we want to skip
mergejoin mark/restore then it must depend only on merge clauses.
To avoid adding more planning overhead than absolutely necessary,
the present patch errs in the conservative direction: there are cases
where inner_unique or skip_mark_restore processing could be used, but
it will not do so because it's not sure that the uniqueness proof
depended only on "safe" clauses.  This could be improved later.

David Rowley, reviewed and rather heavily editorialized on by me

Discussion: https://postgr.es/m/CAApHDvqF6Sw-TK98bW48TdtFJ+3a7D2mFyZ7++=D-RyPsL76gw@mail.gmail.com
This commit is contained in:
Tom Lane
2017-04-07 22:20:03 -04:00
parent f13a9121f9
commit 9c7f5229ad
26 changed files with 987 additions and 206 deletions
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69
contrib/postgres_fdw/expected/postgres_fdw.out
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@ -396,13 +396,14 @@ EXPLAIN (VERBOSE, COSTS OFF)
Output: t1.c1, t2."C 1"
-> Merge Join
Output: t1.c1, t2."C 1"
Inner Unique: true
Merge Cond: (t1.c1 = t2."C 1")
-> Foreign Scan on public.ft2 t1
Output: t1.c1
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-> Index Only Scan using t1_pkey on "S 1"."T 1" t2
Output: t2."C 1"
(10 rows)
(11 rows)
SELECT t1.c1, t2."C 1" FROM ft2 t1 JOIN "S 1"."T 1" t2 ON (t1.c1 = t2."C 1") OFFSET 100 LIMIT 10;
c1 | C 1
@ -429,13 +430,14 @@ EXPLAIN (VERBOSE, COSTS OFF)
Output: t1.c1, t2."C 1"
-> Merge Left Join
Output: t1.c1, t2."C 1"
Inner Unique: true
Merge Cond: (t1.c1 = t2."C 1")
-> Foreign Scan on public.ft2 t1
Output: t1.c1
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-> Index Only Scan using t1_pkey on "S 1"."T 1" t2
Output: t2."C 1"
(10 rows)
(11 rows)
SELECT t1.c1, t2."C 1" FROM ft2 t1 LEFT JOIN "S 1"."T 1" t2 ON (t1.c1 = t2."C 1") OFFSET 100 LIMIT 10;
c1 | C 1
@ -462,6 +464,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Output: t1."C 1"
-> Merge Right Join
Output: t1."C 1"
Inner Unique: true
Merge Cond: (t3.c1 = t1."C 1")
-> Foreign Scan
Output: t3.c1
@ -469,7 +472,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Remote SQL: SELECT r3."C 1" FROM ("S 1"."T 1" r2 INNER JOIN "S 1"."T 1" r3 ON (((r2."C 1" = r3."C 1")))) ORDER BY r2."C 1" ASC NULLS LAST
-> Index Only Scan using t1_pkey on "S 1"."T 1" t1
Output: t1."C 1"
(11 rows)
(12 rows)
SELECT t1."C 1" FROM "S 1"."T 1" t1 left join ft1 t2 join ft2 t3 on (t2.c1 = t3.c1) on (t3.c1 = t1."C 1") OFFSET 100 LIMIT 10;
C 1
@ -497,6 +500,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Output: t1."C 1", t2.c1, t3.c1
-> Merge Right Join
Output: t1."C 1", t2.c1, t3.c1
Inner Unique: true
Merge Cond: (t3.c1 = t1."C 1")
-> Foreign Scan
Output: t3.c1, t2.c1
@ -504,7 +508,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Remote SQL: SELECT r3."C 1", r2."C 1" FROM ("S 1"."T 1" r3 LEFT JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r3."C 1")))) ORDER BY r3."C 1" ASC NULLS LAST
-> Index Only Scan using t1_pkey on "S 1"."T 1" t1
Output: t1."C 1"
(11 rows)
(12 rows)
SELECT t1."C 1", t2.c1, t3.c1 FROM "S 1"."T 1" t1 left join ft1 t2 full join ft2 t3 on (t2.c1 = t3.c1) on (t3.c1 = t1."C 1") OFFSET 100 LIMIT 10;
C 1 | c1 | c1
@ -530,6 +534,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Output: t1."C 1", t2.c1, t3.c1
-> Merge Full Join
Output: t1."C 1", t2.c1, t3.c1
Inner Unique: true
Merge Cond: (t3.c1 = t1."C 1")
-> Foreign Scan
Output: t2.c1, t3.c1
@ -537,7 +542,7 @@ EXPLAIN (VERBOSE, COSTS OFF)
Remote SQL: SELECT r2."C 1", r3."C 1" FROM ("S 1"."T 1" r2 FULL JOIN "S 1"."T 1" r3 ON (((r2."C 1" = r3."C 1")))) ORDER BY r3."C 1" ASC NULLS LAST
-> Index Only Scan using t1_pkey on "S 1"."T 1" t1
Output: t1."C 1"
(11 rows)
(12 rows)
SELECT t1."C 1", t2.c1, t3.c1 FROM "S 1"."T 1" t1 full join ft1 t2 full join ft2 t3 on (t2.c1 = t3.c1) on (t3.c1 = t1."C 1") OFFSET 100 LIMIT 10;
C 1 | c1 | c1
@ -1844,8 +1849,8 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
-- SEMI JOIN, not pushed down
EXPLAIN (VERBOSE, COSTS OFF)
SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
QUERY PLAN
---------------------------------------------------------------------------------------------
QUERY PLAN
---------------------------------------------------------------------------------------
Limit
Output: t1.c1
-> Merge Semi Join
@ -1854,12 +1859,10 @@ SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1)
-> Foreign Scan on public.ft1 t1
Output: t1.c1
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-> Materialize
-> Foreign Scan on public.ft2 t2
Output: t2.c1
-> Foreign Scan on public.ft2 t2
Output: t2.c1
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
(13 rows)
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
(11 rows)
SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
c1
@ -1889,12 +1892,10 @@ SELECT t1.c1 FROM ft1 t1 WHERE NOT EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2
-> Foreign Scan on public.ft1 t1
Output: t1.c1
Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-> Materialize
-> Foreign Scan on public.ft2 t2
Output: t2.c2
-> Foreign Scan on public.ft2 t2
Output: t2.c2
Remote SQL: SELECT c2 FROM "S 1"."T 1" ORDER BY c2 ASC NULLS LAST
(13 rows)
Remote SQL: SELECT c2 FROM "S 1"."T 1" ORDER BY c2 ASC NULLS LAST
(11 rows)
SELECT t1.c1 FROM ft1 t1 WHERE NOT EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c2) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
c1
@ -3121,6 +3122,7 @@ select count(*), x.b from ft1, (select c2 a, sum(c1) b from ft1 group by c2) x w
Group Key: x.b
-> Hash Join
Output: x.b
Inner Unique: true
Hash Cond: (ft1.c2 = x.a)
-> Foreign Scan on public.ft1
Output: ft1.c2
@ -3133,7 +3135,7 @@ select count(*), x.b from ft1, (select c2 a, sum(c1) b from ft1 group by c2) x w
Output: ft1_1.c2, (sum(ft1_1.c1))
Relations: Aggregate on (public.ft1)
Remote SQL: SELECT c2, sum("C 1") FROM "S 1"."T 1" GROUP BY c2
(20 rows)
(21 rows)
select count(*), x.b from ft1, (select c2 a, sum(c1) b from ft1 group by c2) x where ft1.c2 = x.a group by x.b order by 1, 2;
count | b
@ -3252,6 +3254,7 @@ select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.
Output: sum(q.a), count(q.b)
-> Nested Loop Left Join
Output: q.a, q.b
Inner Unique: true
Join Filter: ((ft4.c1)::numeric <= q.b)
-> Foreign Scan on public.ft4
Output: ft4.c1, ft4.c2, ft4.c3
@ -3264,7 +3267,7 @@ select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.
Output: 13, (avg(ft1.c1)), NULL::bigint
Relations: Aggregate on ((public.ft2) LEFT JOIN (public.ft1))
Remote SQL: SELECT 13, avg(r1."C 1"), NULL::bigint FROM ("S 1"."T 1" r2 LEFT JOIN "S 1"."T 1" r1 ON (((r1."C 1" = r2."C 1"))))
(16 rows)
(17 rows)
select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.c1) from ft1 right join ft2 on (ft1.c1 = ft2.c1)) q(a, b, c) on (ft4.c1 <= q.b);
sum | count
@ -4048,20 +4051,18 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
explain (verbose, costs off) select * from ft3 f, loct3 l
where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
QUERY PLAN
-------------------------------------------------------------
Hash Join
QUERY PLAN
---------------------------------------------------------
Nested Loop
Output: f.f1, f.f2, f.f3, l.f1, l.f2, l.f3
Hash Cond: ((f.f3)::text = (l.f3)::text)
Join Filter: ((f.f3)::text = (l.f3)::text)
-> Index Scan using loct3_f1_key on public.loct3 l
Output: l.f1, l.f2, l.f3
Index Cond: (l.f1 = 'foo'::text)
-> Foreign Scan on public.ft3 f
Output: f.f1, f.f2, f.f3
Remote SQL: SELECT f1, f2, f3 FROM public.loct3
-> Hash
Output: l.f1, l.f2, l.f3
-> Index Scan using loct3_f1_key on public.loct3 l
Output: l.f1, l.f2, l.f3
Index Cond: (l.f1 = 'foo'::text)
(11 rows)
(9 rows)
-- ===================================================================
-- test writable foreign table stuff
@ -6541,6 +6542,7 @@ select * from bar where f1 in (select f1 from foo) for update;
Output: bar.f1, bar.f2, bar.ctid, bar.*, bar.tableoid, foo.ctid, foo.*, foo.tableoid
-> Hash Join
Output: bar.f1, bar.f2, bar.ctid, bar.*, bar.tableoid, foo.ctid, foo.*, foo.tableoid
Inner Unique: true
Hash Cond: (bar.f1 = foo.f1)
-> Append
-> Seq Scan on public.bar
@ -6559,7 +6561,7 @@ select * from bar where f1 in (select f1 from foo) for update;
-> Foreign Scan on public.foo2
Output: foo2.ctid, foo2.*, foo2.tableoid, foo2.f1
Remote SQL: SELECT f1, f2, f3, ctid FROM public.loct1
(22 rows)
(23 rows)
select * from bar where f1 in (select f1 from foo) for update;
f1 | f2
@ -6578,6 +6580,7 @@ select * from bar where f1 in (select f1 from foo) for share;
Output: bar.f1, bar.f2, bar.ctid, bar.*, bar.tableoid, foo.ctid, foo.*, foo.tableoid
-> Hash Join
Output: bar.f1, bar.f2, bar.ctid, bar.*, bar.tableoid, foo.ctid, foo.*, foo.tableoid
Inner Unique: true
Hash Cond: (bar.f1 = foo.f1)
-> Append
-> Seq Scan on public.bar
@ -6596,7 +6599,7 @@ select * from bar where f1 in (select f1 from foo) for share;
-> Foreign Scan on public.foo2
Output: foo2.ctid, foo2.*, foo2.tableoid, foo2.f1
Remote SQL: SELECT f1, f2, f3, ctid FROM public.loct1
(22 rows)
(23 rows)
select * from bar where f1 in (select f1 from foo) for share;
f1 | f2
@ -6618,6 +6621,7 @@ update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
Remote SQL: UPDATE public.loct2 SET f2 = $2 WHERE ctid = $1
-> Hash Join
Output: bar.f1, (bar.f2 + 100), bar.ctid, foo.ctid, foo.*, foo.tableoid
Inner Unique: true
Hash Cond: (bar.f1 = foo.f1)
-> Seq Scan on public.bar
Output: bar.f1, bar.f2, bar.ctid
@ -6634,6 +6638,7 @@ update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
Remote SQL: SELECT f1, f2, f3, ctid FROM public.loct1
-> Hash Join
Output: bar2.f1, (bar2.f2 + 100), bar2.f3, bar2.ctid, foo.ctid, foo.*, foo.tableoid
Inner Unique: true
Hash Cond: (bar2.f1 = foo.f1)
-> Foreign Scan on public.bar2
Output: bar2.f1, bar2.f2, bar2.f3, bar2.ctid
@ -6649,7 +6654,7 @@ update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
-> Foreign Scan on public.foo2
Output: foo2.ctid, foo2.*, foo2.tableoid, foo2.f1
Remote SQL: SELECT f1, f2, f3, ctid FROM public.loct1
(37 rows)
(39 rows)
update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
select tableoid::regclass, * from bar order by 1,2;