Re: Extend more usecase for planning time partition pruning and init partition pruning. - Mailing list pgsql-hackers

On Sun, Jan 24, 2021 at 6:34 PM Andy Fan <zhihui.fan1213@gmail.com> wrote:

Hi:

 I recently found a use case like this.  SELECT * FROM p, q WHERE p.partkey =
 q.colx AND (q.colx = $1 OR q.colx = $2); Then we can't do either planning time
 partition prune or init partition prune.  Even though we have run-time
 partition pruning work at last, it is too late in some cases since we have
 to init all the plan nodes in advance.  In my case, there are 10+
 partitioned relation in one query and the execution time is short, so the
 init plan a lot of plan nodes cares a lot.

The attached patches fix this issue. It just get the "p.partkey = q.colx"
case in root->eq_classes or rel->joinlist (outer join), and then check if there
is some baserestrictinfo in another relation which can be used for partition
pruning. To make the things easier, both partkey and colx must be Var
expression in implementation.

- v1-0001-Make-some-static-functions-as-extern-and-extend-C.patch

Just some existing refactoring and extending ChangeVarNodes to be able

to change var->attno.

- v1-0002-Build-some-implied-pruning-quals-to-extend-the-us.patch

Do the real job.

Thought?

--

Best Regards

Andy Fan (https://www.aliyun.com/)

Some results from this patch. 

create table p (a int, b int, c character varying(8)) partition by list(c);
create table p1  partition of p for values in ('000001');
create table p2  partition of p for values in ('000002');
create table p3  partition of p for values in ('000003');
create table q (a int, c character varying(8), b int) partition by list(c);
create table q1  partition of q for values in ('000001');
create table q2  partition of q for values in ('000002');
create table q3  partition of q for values in ('000003');

Before the patch:
postgres=# explain (costs off) select * from p inner join q on p.c = q.c and q.c > '000002';
                     QUERY PLAN
----------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Append
         ->  Seq Scan on p1 p_1
         ->  Seq Scan on p2 p_2
         ->  Seq Scan on p3 p_3
   ->  Hash
         ->  Seq Scan on q3 q
               Filter: ((c)::text > '000002'::text)
(9 rows)

After the patch:

                     QUERY PLAN
----------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Seq Scan on p3 p
   ->  Hash
         ->  Seq Scan on q3 q
               Filter: ((c)::text > '000002'::text)
(6 rows)


Before the patch:
postgres=# explain (costs off) select * from p inner join q on p.c = q.c and (q.c = '000002' or q.c = '000001');
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Append
         ->  Seq Scan on p1 p_1
         ->  Seq Scan on p2 p_2
         ->  Seq Scan on p3 p_3
   ->  Hash
         ->  Append
               ->  Seq Scan on q1 q_1
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
               ->  Seq Scan on q2 q_2
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
(12 rows)

After the patch:
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Append
         ->  Seq Scan on p1 p_1
         ->  Seq Scan on p2 p_2
   ->  Hash
         ->  Append
               ->  Seq Scan on q1 q_1
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
               ->  Seq Scan on q2 q_2
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
(11 rows)

Before the patch:
postgres=# explain (costs off) select * from p left join q on p.c = q.c where (q.c = '000002' or q.c = '000001');
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Append
         ->  Seq Scan on p1 p_1
         ->  Seq Scan on p2 p_2
         ->  Seq Scan on p3 p_3
   ->  Hash
         ->  Append
               ->  Seq Scan on q1 q_1
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
               ->  Seq Scan on q2 q_2
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
(12 rows)

After the patch:
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Hash Join
   Hash Cond: ((p.c)::text = (q.c)::text)
   ->  Append
         ->  Seq Scan on p1 p_1
         ->  Seq Scan on p2 p_2
   ->  Hash
         ->  Append
               ->  Seq Scan on q1 q_1
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
               ->  Seq Scan on q2 q_2
                     Filter: (((c)::text = '000002'::text) OR ((c)::text = '000001'::text))
(11 rows)

--

Best Regards

Andy Fan (https://www.aliyun.com/)