Re: Problem with default partition pruning

Hi Alvaro,

Thanks for reviewing.
The modification you made seems correct to me.

However, I'm still concerned that the block
-----
if (partconstr)
{
partconstr = (List *)
expression_planner((Expr *) partconstr);
if (context->rel->relid != 1)
ChangeVarNodes((Node *) partconstr, 1,
context->rel->relid, 0);
if (predicate_refuted_by(partconstr,
list_make1(clause),
false))
{
context->contradictory = true;
return NIL;
}
}
-----
is written in the right place as Amit explained [1].

At first, we tried to fix the following problematic query
which was reported by Thibaut before:

create table p (a int) partition by range (a);
create table p1 partition of p for values from (0) to (20) partition
by range (a);
create table p11 partition of p1 for values from (0) to (10);
create table p1_def partition of p1 default;
explain select * from p1 where a = 25 or a = 5;
QUERY PLAN
──────────────────────────────────────
Append (cost=0.00..96.75 rows=50 width=4)
-> Seq Scan on p11 (cost=0.00..48.25 rows=25 width=4)
Filter: ((a = 25) OR (a = 5))
-> Seq Scan on p1_def (cost=0.00..48.25 rows=25 width=4)
Filter: ((a = 25) OR (a = 5))
(5 rows)

And Amit proposed the patch to fix this problem[2].
In this patch, the above if() block was written in another place.
After that, I found the following query also doesn't work correctly:

explain select * from p1 where a = 25;
QUERY PLAN
───────────────────────────────────────
Append (cost=0.00..41.94 rows=13 width=4)
-> Seq Scan on p1_def (cost=0.00..41.88 rows=13 width=4)
Filter: (a = 25)
(3 rows)

So I proposed moving the if() block to the current place.
The latest patch can solve both queries but I found the latter
problem can be solved by setting constraint_exclusion = on.

Which approach will be suitable?

[1] https://www.postgresql.org/message-id/CA%2BHiwqG%2BnSD0vcJacArYgYcFVtpTJQ0fx1gBgoZkA_isKd6Z2w%40mail.gmail.com
[2] https://www.postgresql.org/message-id/9bb31dfe-b0d0-53f3-3ea6-e64b811424cf%40lab.ntt.co.jp

Best regards,

Yuzuko Hosoya
NTT Open Source Software Center

On Mon, Aug 5, 2019 at 11:03 AM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
>
> I propose the comment rewordings as attached. Mostly, this updates the
> comment atop the function to cover the case being modified, and then the
> new comment just refers to the new explicitly stated policy, so it
> bcomes simpler.
>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

--
Best regards,
Yuzuko Hosoya
NTT Open Source Software Center