Re: [HACKERS] Partition-wise join for join between (declaratively)partitioned tables

On Thu, Jul 20, 2017 at 7:00 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> I think the problem is that the row count estimates for the child
> joins seem to be totally bogus:
>
> ->  Hash Semi Join  (cost=309300.53..491665.60 rows=1 width=12)
> (actual time=10484.422..15945.851 rows=1523493 loops=3)
>   Hash Cond: (l1.l_orderkey = l2.l_orderkey)
>   Join Filter: (l2.l_suppkey <> l1.l_suppkey)
>   Rows Removed by Join Filter: 395116
>
> That's clearly wrong.  In the un-partitioned plan, the join to l2
> produces about as many rows of output as the number of rows that were
> input (998433 vs. 962909); but here, a child join with a million rows
> as input is estimated to produce only 1 row of output.  I bet the
> problem is that the child-join's row count estimate isn't getting
> initialized at all, but then something is clamping it to 1 row instead
> of 0.
>
> So this looks like a bug in Ashutosh's patch.

Isn't this the same as the issue reported here?

https://www.postgresql.org/message-id/flat/CAEepm%3D270ze2hVxWkJw-5eKzc3AB4C9KpH3L2kih75R5pdSogg%40mail.gmail.com

-- 
Thomas Munro
http://www.enterprisedb.com