I have a problem with a part of big query because of incorrect
estimation. It's easy to emulate the case:
create table a (id bigint, id2 bigint);
create table b (id bigint, id2 bigint);
insert into a (id, id2)
select random() * 100000, random() * 100
from generate_series(1, 100000);
insert into b (id, id2)
select id, case when random() < 0.1 then random() * 100 else id2 end
from a;
alter table a alter column id set statistics 1000;
alter table a alter column id2 set statistics 1000;
alter table b alter column id set statistics 1000;
alter table b alter column id2 set statistics 1000;
analyze a;
analyze b;
explain analyze
select *
from a
join b on b.id = a.id and b.id2 = a.id2;
"Hash Join (cost=1161.00..3936.15 rows=1661 width=32) (actual
time=424.865..1128.194 rows=91268 loops=1)"
" Hash Cond: ((a.id = b.id) AND (a.id2 = b.id2))"
" -> Seq Scan on a (cost=0.00..791.00 rows=100000 width=16) (actual
time=0.013..197.908 rows=100000 loops=1)"
" -> Hash (cost=791.00..791.00 rows=100000 width=16) (actual
time=424.777..424.777 rows=100000 loops=1)"
" -> Seq Scan on b (cost=0.00..791.00 rows=100000 width=16)
(actual time=0.010..197.536 rows=100000 loops=1)"
"Total runtime: 1305.121 ms"
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