Re: Bogus nestloop rows estimate in 8.4.7

On Mon, May 28, 2012 at 10:32 PM, Marti Raudsepp <marti(at)juffo(dot)org> wrote:
> There was a similar case in 9.0.4 with WHERE i=1, but that has been
> fixed in 9.0.7

Oh, it's been fixed in 9.0.7, but apparently not in 8.4.11; the empty
parent tables are confusing the estimate:

explain select * from a_parent join b_parent using (i) where i=1;

QUERY PLAN
Nested Loop (cost=56.57..123.65 rows=224 width=4)
-> Append (cost=0.00..62.60 rows=16 width=4)
-> Seq Scan on b_parent (cost=0.00..40.00 rows=12 width=4)
Filter: (i = 1)
-> Index Scan using b2_i_idx on b_child2 b_parent
(cost=0.00..11.30 rows=2 width=4)
Index Cond: (i = 1)
-> Index Scan using b1_i_idx on b_child1 b_parent
(cost=0.00..11.30 rows=2 width=4)
Index Cond: (i = 1)
-> Materialize (cost=56.57..56.71 rows=14 width=4)
-> Append (cost=0.00..56.56 rows=14 width=4)
-> Seq Scan on a_parent (cost=0.00..40.00 rows=12 width=4)
Filter: (i = 1)
-> Index Scan using a1_i_idx on a_child1 a_parent
(cost=0.00..8.28 rows=1 width=4)
Index Cond: (i = 1)
-> Index Scan using a2_i_idx on a_child2 a_parent
(cost=0.00..8.28 rows=1 width=4)
Index Cond: (i = 1)

Regards,
Marti