RE: BUG #17413: update of partitioned table via postgres_fdw updates to much rows

I propose to add secondary check of all field values from the where condition.
So in that particular case it could be something like that

update part_update_test
set field=$2
where ctid=$1
and id = $3
and date_id = $4;

Generally speaking it can even improve performance dur to partition pruning.

-----Original Message-----
From: Japin Li <japinli(at)hotmail(dot)com>
Sent: Tuesday, February 22, 2022 7:09 PM
To: stepya(at)ukr(dot)net; pgsql-bugs(at)lists(dot)postgresql(dot)org
Subject: Re: BUG #17413: update of partitioned table via postgres_fdw updates to much rows

On Tue, 22 Feb 2022 at 18:03, PG Bug reporting form <noreply(at)postgresql(dot)org> wrote:
> The following bug has been logged on the website:
>
> Bug reference: 17413
> Logged by: Stepan Yankevych
> Email address: stepya(at)ukr(dot)net
> PostgreSQL version: 14.2
> Operating system: CentOS
> Description:
>
> We noticed that update foreign table in some cases passes following
> update to the remote DB update part_update_test set field=$2 where
> ctid=$1 In that case one row from each partition can be updated.
> See steps to reproduce
>
> -- pgprod1
> drop table if exists trash.part_update_test;
>
> CREATE TABLE trash.part_update_test (
> id serial,
> date_id int4 NOT NULL,
> simple_text varchar
> ) PARTITION BY RANGE (date_id);
>
> CREATE TABLE trash.part_update_test_20220221 PARTITION OF
> trash.part_update_test FOR VALUES FROM (20220221) TO (20220222);
> CREATE TABLE trash.part_update_test_20220222 PARTITION OF
> trash.part_update_test FOR VALUES FROM (20220222) TO (20220223);
> CREATE TABLE trash.part_update_test_20220223 PARTITION OF
> trash.part_update_test FOR VALUES FROM (20220223) TO (20220224);
>
> insert into trash.part_update_test (date_id, simple_text) values
> (20220221, 'Im 20220221'),(20220222, 'I amd 20220222'),(20220223, 'I
> am the third row ');
>
> select ctid, *
> from trash.part_update_test;
>
> ctid |id|date_id |simple_text |
> -----+--+--------+-------------------+
> (0,1)| 1|20220221|Im 20220221 |
> (0,1)| 2|20220222|I amd 20220222 |
> (0,1)| 3|20220223|I am the third row |
>
> -- pgprod2
> DROP FOREIGN TABLE if EXISTS staging.part_update_test; IMPORT FOREIGN
> SCHEMA "trash" LIMIT TO (part_update_test) FROM SERVER postgresprod
> into staging;
>
>
> with ids as materialized (select 1 as id, 20220221 as date_id )
> update staging.part_update_test t set simple_text = 'I am updated
> version of 20220221 '
> from ids
> where t.id = ids.id
> and t.date_id = ids.date_id ;
>
> select ctid, *
> from staging.part_update_test;
>
> ctid |id|date_id |simple_text |
> -----+--+--------+----------------------------------+
> (0,2)| 1|20220221|I am updated version of 20220221 | (0,2)|
> 2|20220222|I am updated version of 20220221 | (0,2)| 3|20220223|I am
> updated version of 20220221 |
>
> As you can see all of rows that had (0,1) where updated , but the only
> first row with ID =1 had to be updated .
> The same was reproducible at least in PG14.1

Yeah, it is a bug IMO. The deparseUpdateSql() function assume that the tuple id is as unique, however, it ignores the partitioned table, in which the tuple id may be duplicated.

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.