Re: query plan

=?UTF-8?Q?Torsten_F=C3=B6rtsch?= <tfoertsch123(at)gmail(dot)com> writes:
> This is part of a query plan:

> Nested Loop Left Join (cost=26.32..47078866.36 rows=1344945195 width=626)
> -> Nested Loop Left Join (cost=25.74..5312.48 rows=1344945195
> width=608)
> -> Nested Loop Left Join (cost=6.79..2876.77 rows=102 width=373)
> -> Nested Loop Left Join (cost=1.90..1965.51 rows=102
> width=361)
> -> Bitmap Heap Scan on ... (cost=4.89..8.91 rows=2
> width=28)
> -> Hash Left Join (cost=18.95..42.61 rows=3 width=243)
> -> Hash Left Join (cost=18.94..42.59 rows=3 width=203)
> -> Hash (cost=0.00..0.00 rows=1 width=48)
> -> Memoize (cost=0.58..4.59 rows=1 width=172)

> What I don't understand is this. The left node of the join is expected to
> return 102 rows. The right node 3. How can this result in >1e9 rows?

The rowcount estimate for the join is not derived by multiplying the
rowcount estimates of the two inputs. Having said that, this looks
pretty inconsistent. Can you show a test case that acts like that?

regards, tom lane