Re: EvalPlanQual behaves oddly for FDW queries involving system columns

Hi Fujita-san,
I am having some minor problems running this repro

On Thu, Jan 15, 2015 at 12:45 PM, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp
> wrote:

> Here is an example using postgres_fdw.
>
> [Terminal 1]
> postgres=# create table t (a int, b int);
> CREATE TABLE
> postgres=# insert into t values (1, 1);
> INSERT 0 1
> postgres=# begin;
> BEGIN
> postgres=# update t set b = b * 2;
> UPDATE 1
>
> [Terminal 2]
> postgres=# create foreign table ft (a int) server loopback options
> (table_name 'lbt');
>

There isn't any table "lbt" mentioned here. Do you mean "t" here?

> CREATE FOREIGN TABLE
> postgres=# insert into ft values (1);
> INSERT 0 1
> postgres=# select tableoid, ctid, * from ft;
> tableoid | ctid | a
> ----------+-------+---
> 25092 | (0,1) | 1
> (1 row)
>

Shouldn't we see two values here one inserted in 't' and one in "ft"

>
> postgres=# select ft.tableoid, ft.ctid, ft.* from t, ft where t.a = ft.a
> for update;
>
> [Terminal 1]
> postgres=# commit;
> COMMIT
>
> [Terminal 2]
> postgres=# select ft.tableoid, ft.ctid, ft.* from t, ft where t.a = ft.a
> for update;
> tableoid | ctid | a
> ----------+----------------+---
> 0 | (4294967295,0) | 1
> (1 row)
>
>
Instead of this result, I got following error
ERROR: could not serialize access due to concurrent update
CONTEXT: Remote SQL command: SELECT a, ctid FROM public.t FOR UPDATE

Am I missing something while reproducing the problem?

> Note that tableoid and ctid have been changed!
>
> I think the reason for that is because EvalPlanQualFetchRowMarks doesn't
> properly set tableoid and ctid for foreign tables, IIUC. I think this
> should be fixed. Please find attached a patch. The patch slightly
> relates to [1], so if it is reasonable, I'll update [1] on top of this.
>
> [1] https://commitfest.postgresql.org/action/patch_view?id=1386
>
> Best regards,
> Etsuro Fujita
>
>
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--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company