Re: force partition pruning

[Vijaykumar Jain <vijaykumarjain.github@xxxxxxxxx>]

ok,

partitioning - Can PostgreSQL 12 do partition pruning at execution time with subquery returning a list? - Stack Overflow

ok forcing hash join off, did not work as the outer table was the partitioned table selected.

On Tue, 11 May 2021 at 22:42, Vijaykumar Jain <vijaykumarjain.github@xxxxxxxxx> wrote:

Ok. maybe you are in a rush.

But I would keep the thread open, to understand what I am not understanding or else, it'll become a habit of converting sql to plpgsql :)

Big Guys,

It seems, when the table is partitioned by range, it makes use of a nested loop which helps in partition pruning.

if the table is list partitioned, it scans all the partitions.

Is this expected ?

LIST BASED PARTITION

**********************

postgres@go:~$ more p.sql

drop table tbl1;

drop table tprt;

create table tbl1(col1 int);

insert into tbl1 values (501), (505);

-- Basic table

create table tprt (col1 int) partition by list (col1);

create table tprt_1 partition of tprt for values in (501);

create table tprt_2 partition of tprt for values in (1001);

create table tprt_3 partition of tprt for values in  (2001);

create table tprt_4 partition of tprt for values in  (3001);

create table tprt_5 partition of tprt for values in  (4001);

create table tprt_6 partition of tprt for values in  (5001);

create index tprt1_idx on tprt_1 (col1);

create index tprt2_idx on tprt_2 (col1);

create index tprt3_idx on tprt_3 (col1);

create index tprt4_idx on tprt_4 (col1);

create index tprt5_idx on tprt_5 (col1);

create index tprt6_idx on tprt_6 (col1);

insert into tprt values (501), (1001), (2001), (3001), (4001), (5001), (501);

alter table tbl1 add column col2 int default 0;

update tbl1 set col2 =1 where col1 = 501;

vacuum analyze tprt;

vacuum analyze tbl1;

explain analyze select * from tprt where tprt.col1 in (select tbl1.col1 from tbl1 where tbl1.col2 in (1, 2) );

                                                 QUERY PLAN

------------------------------------------------------------------------------------------------------------

 Hash Semi Join  (cost=1.05..7.20 rows=2 width=4) (actual time=0.028..0.034 rows=2 loops=1)

   Hash Cond: (tprt.col1 = tbl1.col1)

   ->  Append  (cost=0.00..6.10 rows=7 width=4) (actual time=0.003..0.008 rows=7 loops=1)

         ->  Seq Scan on tprt_1  (cost=0.00..1.02 rows=2 width=4) (actual time=0.002..0.003 rows=2 loops=1)

         ->  Seq Scan on tprt_2  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_3  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_4  (cost=0.00..1.01 rows=1 width=4) (actual time=0.000..0.000 rows=1 loops=1)

         ->  Seq Scan on tprt_5  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_6  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

   ->  Hash  (cost=1.02..1.02 rows=2 width=4) (actual time=0.006..0.006 rows=1 loops=1)

         Buckets: 1024  Batches: 1  Memory Usage: 9kB

         ->  Seq Scan on tbl1  (cost=0.00..1.02 rows=2 width=4) (actual time=0.003..0.003 rows=1 loops=1)

               Filter: (col2 = ANY ('{1,2}'::integer[]))

               Rows Removed by Filter: 1

 Planning Time: 0.237 ms

 Execution Time: 0.060 ms

even if i set hashjoin off

postgres=# set enable_hashjoin TO 0;

SET

postgres=# explain analyze select * from tprt where tprt.col1 in (select tbl1.col1 from tbl1 where tbl1.col2 in (1, 2) );

                                                 QUERY PLAN

------------------------------------------------------------------------------------------------------------

 Nested Loop Semi Join  (cost=0.00..7.34 rows=2 width=4) (actual time=0.013..0.023 rows=2 loops=1)

   Join Filter: (tprt.col1 = tbl1.col1)

   Rows Removed by Join Filter: 5

   ->  Append  (cost=0.00..6.10 rows=7 width=4) (actual time=0.004..0.010 rows=7 loops=1)

         ->  Seq Scan on tprt_1  (cost=0.00..1.02 rows=2 width=4) (actual time=0.003..0.003 rows=2 loops=1)

         ->  Seq Scan on tprt_2  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_3  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_4  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_5  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

         ->  Seq Scan on tprt_6  (cost=0.00..1.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

   ->  Materialize  (cost=0.00..1.03 rows=2 width=4) (actual time=0.001..0.001 rows=1 loops=7)

         ->  Seq Scan on tbl1  (cost=0.00..1.02 rows=2 width=4) (actual time=0.007..0.007 rows=1 loops=1)

               Filter: (col2 = ANY ('{1,2}'::integer[]))

               Rows Removed by Filter: 1

 Planning Time: 0.578 ms

 Execution Time: 0.038 ms

(16 rows)

**********************

RANGE BASED PARTITION

**********************

postgres@go:~$ more q.sql

drop table tbl1;

drop table tprt;

create table tbl1(col1 int);

insert into tbl1 values (501), (505);

-- Basic table

create table tprt (col1 int) partition by range(col1);

create table tprt_1 partition of tprt for values from (0) to (500);

create table tprt_2 partition of tprt for values from (500) to (1000);

create table tprt_3 partition of tprt for values from (1000) to (1500);

create table tprt_4 partition of tprt for values from (1500) to (2000);

create table tprt_5 partition of tprt for values from (2000) to (22500);

create index tprt1_idx on tprt_1 (col1);

create index tprt2_idx on tprt_2 (col1);

create index tprt3_idx on tprt_3 (col1);

create index tprt4_idx on tprt_4 (col1);

create index tprt5_idx on tprt_5 (col1);

insert into tprt values (501), (1001), (2001), (3001), (4001), (5001), (501);

vacuum analyze tbl1;

vacuum analyze tprt;

alter table tbl1 add column col2 int default 0;

update tbl1 set col2 =1 where col1 = 501;

explain analyze select * from tprt where tprt.col1 in (select tbl1.col1 from tbl1 where tbl1.col2 in (1, 2) );

                                                   QUERY PLAN

----------------------------------------------------------------------------------------------------------------

 Nested Loop  (cost=3.29..55.37 rows=2 width=4) (actual time=0.016..0.018 rows=2 loops=1)

   ->  Unique  (cost=1.03..1.04 rows=2 width=4) (actual time=0.012..0.012 rows=1 loops=1)

         ->  Sort  (cost=1.03..1.04 rows=2 width=4) (actual time=0.011..0.011 rows=1 loops=1)

               Sort Key: tbl1.col1

               Sort Method: quicksort  Memory: 25kB

               ->  Seq Scan on tbl1  (cost=0.00..1.02 rows=2 width=4) (actual time=0.004..0.005 rows=1 loops=1)

                     Filter: (col2 = ANY ('{1,2}'::integer[]))

                     Rows Removed by Filter: 1

   ->  Append  (cost=2.26..26.86 rows=30 width=4) (actual time=0.003..0.004 rows=2 loops=1)

         ->  Bitmap Heap Scan on tprt_1  (cost=2.26..11.81 rows=13 width=4) (never executed)

               Recheck Cond: (col1 = tbl1.col1)

               ->  Bitmap Index Scan on tprt1_idx  (cost=0.00..2.25 rows=13 width=0) (never executed)

                     Index Cond: (col1 = tbl1.col1)

         ->  Seq Scan on tprt_2  (cost=0.00..1.02 rows=2 width=4) (actual time=0.001..0.002 rows=2 loops=1)

               Filter: (tbl1.col1 = col1)

         ->  Seq Scan on tprt_3  (cost=0.00..1.01 rows=1 width=4) (never executed)

               Filter: (tbl1.col1 = col1)

         ->  Bitmap Heap Scan on tprt_4  (cost=2.26..11.81 rows=13 width=4) (never executed)

               Recheck Cond: (col1 = tbl1.col1)

               ->  Bitmap Index Scan on tprt4_idx  (cost=0.00..2.25 rows=13 width=0) (never executed)

                     Index Cond: (col1 = tbl1.col1)

         ->  Seq Scan on tprt_5  (cost=0.00..1.05 rows=1 width=4) (never executed)

               Filter: (tbl1.col1 = col1)

 Planning Time: 0.214 ms

 Execution Time: 0.069 ms

(25 rows)

**********************

On Tue, 11 May 2021 at 17:44, Niels Jespersen <NJN@xxxxxx> wrote:

> 

>Sorry,

> 

>I made a major mistake. I somehow saw the period and period_version as the same.

>so, yes partitions are not pruned here. So my suggestion makes no sense.

 

Thats quite ok. I think my plan now is to have a table returning function that executes a query dynamically. The query has a where caluse that is first constructed.

 

Like this:

 

 

return query execute format('select d.x, d.y from %1$I.%1$I d where d.period_version = any(' || quote_literal(_periode_version_array) ||'::text[])', register_in);

 

Regards Niels

 

 

--

Thanks,

Vijay

Mumbai, India

--

Thanks,

Vijay

Mumbai, India