Re: Removing [Merge]Append nodes which contain a single subpath

On 27 October 2017 at 01:44, Ashutosh Bapat
<ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> I think Antonin has a point. The join processing may deem some base
> relations dummy (See populate_joinrel_with_paths()). So an Append
> relation which had multiple child alive at the end of
> set_append_rel_size() might ultimately have only one child after
> partition-wise join has worked on it.

hmm, I see. partition-wise join is able to remove eliminate partitions
on the other side of the join that can't be matched to:

# set enable_partition_wise_join=on;
SET
# explain select count(*) from ab ab1 inner join ab ab2 on ab1.a=ab2.a
where ab1.a between 1 and 2 and ab2.a between 100000000 and 100000001;
QUERY PLAN
------------------------------------------------
Aggregate (cost=0.00..0.01 rows=1 width=8)
-> Result (cost=0.00..0.00 rows=0 width=0)
One-Time Filter: false
(3 rows)

# \d+ ab
Table "public.ab"
Column | Type | Collation | Nullable | Default | Storage | Stats
target | Description
--------+---------+-----------+----------+---------+---------+--------------+-------------
a | integer | | | | plain | |
b | integer | | | | plain | |
Partition key: RANGE (a)
Partitions: ab_p1 FOR VALUES FROM (1) TO (100000000),
ab_p2 FOR VALUES FROM (100000000) TO (200000000)

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services