Re: [HACKERS] Partition-wise aggregation/grouping

On Tue, Nov 28, 2017 at 12:37 PM, Rajkumar Raghuwanshi <
rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com> wrote:

> On Thu, Nov 23, 2017 at 6:38 PM, Jeevan Chalke
> <jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:
> > Let me know if I missed any comment to be fixed.
>
> Hi,
>
> I have applied v8 patches on commit id 8735978e7aebfbc499843630131c18
> d1f7346c79,
> and getting below observation, please take a look.
>
> Observation:
> "when joining a foreign partition table with local partition table
> getting wrong output
> with partition_wise_join enabled, same is working fine on PG-head
> without aggregates patch."
>

I have observed the same behavior on the master branch too when
partition-wise join path is selected irrespective of this patch-set.

This is happening because data on the foreign table is not compliance with
the partitioning constraints.

> Test-case:
> CREATE EXTENSION postgres_fdw;
> CREATE SERVER pwj_server FOREIGN DATA WRAPPER postgres_fdw OPTIONS
> (dbname 'postgres',port '5432',use_remote_estimate 'true');
> CREATE USER MAPPING FOR PUBLIC SERVER pwj_server;
>
> CREATE TABLE fplt1 (a int, c text) PARTITION BY LIST(c);
> CREATE TABLE fplt1_p1 (a int, c text);
> CREATE TABLE fplt1_p2 (a int, c text);
> CREATE FOREIGN TABLE ftplt1_p1 PARTITION OF fplt1 FOR VALUES IN
> ('0000', '0001', '0002', '0003') SERVER pwj_server OPTIONS (TABLE_NAME
> 'fplt1_p1');
> CREATE FOREIGN TABLE ftplt1_p2 PARTITION OF fplt1 FOR VALUES IN
> ('0004', '0005', '0006', '0007') SERVER pwj_server OPTIONS (TABLE_NAME
> 'fplt1_p2');
> INSERT INTO fplt1_p1 SELECT i, to_char(i%8, 'FM0000') FROM
> generate_series(0, 199, 2) i;
> INSERT INTO fplt1_p2 SELECT i, to_char(i%8, 'FM0000') FROM
> generate_series(200, 398, 2) i;
>
> CREATE TABLE lplt2 (a int, c text) PARTITION BY LIST(c);
> CREATE TABLE lplt2_p1 PARTITION OF lplt2 FOR VALUES IN ('0000',
> '0001', '0002', '0003');
> CREATE TABLE lplt2_p2 PARTITION OF lplt2 FOR VALUES IN ('0004',
> '0005', '0006', '0007');
> INSERT INTO lplt2 SELECT i, to_char(i%8, 'FM0000') FROM
> generate_series(0, 398, 3) i;
>
> SELECT t1.c, t2.c,count(*) FROM fplt1 t1 JOIN lplt2 t2 ON (t1.c = t2.c
> and t1.a = t2.a) WHERE t1.a % 25 = 0 GROUP BY 1,2 ORDER BY t1.c,
> t2.c;
> c | c | count
> ------+------+-------
> 0000 | 0000 | 1
> 0004 | 0004 | 1
> 0006 | 0006 | 1
> (3 rows)
>
> SET enable_partition_wise_join = on;
> SELECT t1.c, t2.c,count(*) FROM fplt1 t1 JOIN lplt2 t2 ON (t1.c = t2.c
> and t1.a = t2.a) WHERE t1.a % 25 = 0 GROUP BY 1,2 ORDER BY t1.c,
> t2.c;
> c | c | count
> ------+------+-------
> 0000 | 0000 | 1
> 0004 | 0004 | 1
> (2 rows)
>
>
> Thanks & Regards,
> Rajkumar Raghuwanshi
> QMG, EnterpriseDB Corporation
>

--
Jeevan Chalke
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company